PARASITES AND PARASITOSIS OF THE DOMESTIC ANIMALS, UNDERHILL 1920

CHAPTER 11 Terms used in parasitology; Symbiosis; Mutualism; Commensalism; Helotism; Parasitism; Phytoparasites; ZoBparasites; Optional occasional parasites; Obligate occasional parasite

PARASITES AND PARASITOSIS

OF THE

PARASITES AND THE PATHOGENESIS AND

BY

B M UNDERHILL, V.M.D.

PROFESSOROP PARASITOLOGYAND INSTRUCTOR IN ZOOLOGYAND

HISTOLOGY, SCHOOL OF VETERINARY MEDICINE,

UNIVER-SITYOF PENNSYLVANIA,ZOOLOGIST, DIVISIONOF

LABORATORIES, PENNSYLVANIA STATE

2fsm ^ork

1920

Bythe MACMILLAN COMPANY

Set up and printed Published April, 1920

In the preparation of this work the author has aimed to present

subject athandasseemsmostessentialtothe needsofthe studentand

thepractitioner Notwithstandingitselementarycharacter, thepresentrapidadvancesin parasitologyhavenecessitatednumerous changes and

additions to the manuscript during its preparation New species and

unsettling factsand theories as tosome whichare notnew are, inthese

days of intensive research, frequently being brought to light and

re-ported upon Some of these findings represent or lead to a distinct

and in themselves imimportant species, they may, by analogy, shedvaluablelightuponlife historiesandmodesof infectionofrelatedforms

these stepsforward thatitmight almostseem better toleave

compara-tive parasitologyatthe present timeto thefragmentalattention ithas

American volume upon the subject may be attributed Be that as it

may,thisbookisnot intendedtobe comprehensive,andit contains but

httle discussion, historical or otherwise, of investigations inthe field of

medicalzoology,—limitationswhichmay, inmeasure, contributetoit alonger period of usefulness inits present form than could behopedfor

in an exhaustive treatise. With but few exceptions, the parasites

con-sidered arethosemostlikelytobemetwithand as towhichmostofthe

facts pertaining to their biology and pathogenicity have been wellestablished

pre-sentingitwith atleast a rudimentalattention tothebiologicprinciples

involvedinparasitism, a knowledge of which isrequisite to the properconception of parasitology and certainly essential to intelligently

beforethe readerintheirtruebearinguponthewholesubjectandrenderthebookparticularlyacceptabletothe generalpractitioner as well as to

thestudent

class-room method of study Of course the student should in everj^

case see the parasite under consideration in so far as this is possible.

vi PREFACE

dissection should, in the author's opinion, be left to the teacher, who

shouldcertainlybe the onebest qualified toformulate the courseadapted

to his needs No general outline, therefore, as to laboratory methodshasbeen attempted

work ofthiskind, the authorfeelsquite sure thatits defects cannot to

any great extent be attributed to that source His observations in thefield and laboratory have beenutilized in the preparation of the book,

but contribute nothing to its pages that is advanced or aggressively

critical. Excluding the first three chapters, so much of the

that thenumerous sources cannot well be enumerated here

of parasitology written byworkersin federal and state bureaus of

ex-perimental research Other sources which have been reliedupon and

freelyused are: M. Neveu-Lemaire'sParasitologic desAnimaux

Johann-sen'sHandbookofMedical Entomology;Calkins' Protozoology;Neumann's

Parasites and Parasitic Diseases of the Domesticated Animals; Braun's

Animal Parasites of Man; The Journal of Parasitology; The American

Edition ofHutyraand Marek, and Osborn'sEconomicZoology

The author wishes to express his sincere appreciation and thanks to'

hislaboratory coworker Dr Fred Boerner, Jr., for hisassistanceinthe

collection of specimens and in the examination of pathologic material;also to Dr William J. Lentz for his reading and valuable criticism ofparts ofthemanuscript,andtoDr C P.Fitchforhishelpfulsuggestions

as to sources of reference

Illustrations for aworkof thischaracterwillbe anaid to the textin

proportion as they are exact and well chosen For the study of

mor-phologic characteristics photographs of actual specimens are often tooobscurein detail,andaccuratedrawingsorlinesketchesare,asarule,ofgreater service It will be observed that many of the figures in this

book are taken from publications issued bythe United States

Depart-mentofAgriculture Probably nobetterdrawingsofthesesubjectshave

been produced, and the privilege granted to use them is esteemed as a

helpfulfavorofmuchvaluetothework Inthis connection theauthor

Bureauof Entomology, to Dr John R Mohler, Chiefof the Bureau of

toDr B H Ransom. Finally, thanksare duetoDr W. H HoedtofPhiladelphia, for his skill and interest in preparing the photomicro-

graphs andmany ofthe drawings

B M. U

PART I

PRELIMINARY CHAPTERS THE EXTERNAL PARASITES

CHAPTER I

PACE

para^-sitism;Thereproductive process inMelophagusovinus;Developmentof the

liver fluke;The tapewormasanexampleofextremeparasitism;Deductions

forms.

CHAPTER 11

Terms used in parasitology; Symbiosis; Mutualism; Commensalism;

Helotism; Parasitism; Phytoparasites; ZoBparasites; Optional occasional

parasites; Obligate occasional parasites; Determinatetransitory parasites;Permanent parasites; Fixed parasites; Erratic parasites; Determinate

erratic parasites; Monoxenous parasites; Heteroxenous parasites;

Hehninthes; Terms used in the designation of parasitic diseases; Predar

ciousandparasitic animals; Factors governing injury to the hostby

para-sites; General etiologic factors.

CHAPTER III

viii CONTENTS

CHAPTER I^•

PAGE

Charactis-tics of the famUy Culicidae; Range and prevalence of mosquitoes; Their

Methodsof distinguishingbetween AnophelesandCulex;Thetransmitter of

of mosquitoes upon live stock; Mosquito control; Characteristics of the

stock; Control; Protection and treatment.

their attack; Protection; Characteristics of the family Muscidse; Thehouse-fly; Habits of the house-flyand its relation to the transmission of disease; Its control; Protective measures;Thehornfly; Its habits; Effect of

Treatment

CHAPTER VI

Myasis; The "screw worm fly;" Its habits; Effect of its attack;

Pro-tective measures; Treatment; The flesh flies; The blowfly; Its habits;

flyandlarvffiuponhorses;Thered-tailed bot-fly; Its habitsandeffect;Thechin fly;Theox bot orwarbleflies; Their life history; Theireconomic im-

at-tack of the flyand its larvce; Protection and treatment.

CHAPTER VII

Differentiation of species; Life history; Relation of fleas to the

transmis-sion of infectious diseases;Treatmentandcontrol.

CHAPTER VIII

CONTENTS ix

PAGE

of thesheep and goat; Pediculosis of the hog; Pediculosis of the dog and

CHAPTER IX

Lice ofPoultry;TheBedbug 82Prevalenceand effect of poultry lice; Species infesting chickens; Species

infesting turkeys; Species infesting ducks and geese; Species infesting

swan; Species infesting pigeons; Control and treatment of poultry lice;

Cimi-cidse;Thecommonbedbug;Its habitsandeffect of its bite;The bedbugas

chiggers, or red bugs; Habits and effect of their attack; Treatment; The

mange, scab, or itch mites; Characteristics of the family Sarcoptidse; The

hosts, and modes of attack; Characteristics of the family Demodeoidae;

De-modecticor follicularmange; Notoedric orheadmangeof the catand

the rabbit; Chorioptic or leg scabies;Symptoms,development,lesions,

diag-nosis,andtransmission ofmangeandscabies.

CHAPTER XI

General considerations; Treatmentof sarcoptic mangeof the horse; Of

of the catandrabbit; Treatmentofdemodecticmange; Treatmentof dectic mange; Treatment of psoroptic scabies of the sheep; of cattle; Of

cattle.

CHAPTER XII

The burrowing miteof poultry; Legmangeor " scaly leg " ; Its course

X CONTENTS

CHAPTER XIII

PAGE

effectuponthe host; Control;Thespinose ear tick; Its habitsandeffectupon

the host;Treatment;Characteristics of the family Ixodidse; Description of

Zool-ogical Division of theUnitedStates BureauofAnimal Industry; Life

development; Lossoccasionedbythe Texas-fever tick; Progressmadein its eradication; Theorder Linguatulida; Linguatula rhinaria of the nasal cavi-

ties ofmammals

PART II

THE INTERNAL PARASITES

CHAPTER XIV

Phyltjm II. Platyhelminthes; The Flukes and Tapeworms 155

Classification of the parasitic worms; Characteristics of the

Platyhelm-inthes; Characteristics of the classTrematoda;TheUverflukes; Theirlife history; Prevalence of fascioliasis; Infection;Migrationof flukes within the

definitive host andpathogenesis; Fascioliasis of the sheep; Fascioliasis of cattle; Controlandtreatment;Theblood fluke; Bilharziosis; Characteristics

of the class Cestoda; Characteristics of the family Taeniidse; Life history of

tapeworms; Their parasitism.

CHAPTER XV

Generalconsideration of the effect oftapewormsupontheir hosts;wormsof the horse;Tapewormsof cattle, sheep, andgoats; Tapewormsof

Tape-the dog; Dog tapeworms in relation to human infection; Tapeworms of

the cat; Tapewormsof the rabbit; Characteristics of the family

Diphyllo-bothriidse; Occurrence of species; Treatment of tseniasis of the dog;

goats,andcattle;Treatmentof tseniasis of the horse.

CHAPTER XVI

CONTENTS xi

CHAPTER XVII

PAGE

cysts;Porkmeasles, Its occurrence;Degenerationandvitality of the cysts;

Measles of the sheep; Ccenurosis or gid; Its occurrence; Its development;

Itspost-mortem appearance;Itssymptoms;Controlandtreatment;

de-velopment; Post-mortem appearance in echinococcosis; Symptoms; trol.

Con-CHAPTER XVIII

PhTLTJMIII. CCELHELMINTHES;ThESmOOTHAND SEGMENTEDROUNDWORMS . 216

Ne-mathelminthes; Characteristics of the order Nematoda: Parasitism of the

nematode worms in general;General considerations as to treatment.

Nematoda; FamilyI AscARiD.ffi!;The Large RoundwormsoftheIntestine 229

Ascar-iasis; Ascarids of the horse; Occurrence of equine ascariasis; Its etiology, control, andtreatment; Characteristics of the family Oxyuridse; Oxyuriasis

As-carids of the ox;Thefamily Heterakidaeandheterakiasis of poultry.

Nematoda; FamilyIV FiLARiroiE;TheThread-likeWorms 244

Nematoda; Family V. Strongylid/e; Subfamily I. Metastrongylin^

Worms op the Respiratory Tract 255

strongy-losis of thesheepandgoat; Itssymptoms,course,andprognosis; Bronchial

and pulmonary strongylosis of cattle; Its symptoms, course, and

prog-nosis; Bronchialand pulmonarystrongylosis of the pig; Its occurenceand

symptoms; Bronchial and pulmonary strongylosis of the horse;

Cardio-pulmonarystrongylosis of the dog;Pulmonarystrongylosis of the cat;

Post-mortem appearance in bronchial and pulmonary strongylosis; ment,etiology, control,and treatmentof bronchialand pulmonarystrongy-

Develop-XII CONTENTS

CHAPTER XXII

PAGENematoda; Subfamily II. Tbichostrongylin^; Worms or the Stomach

strongylosis of the sheepandgoat; Its occurrence; Its symptoms;

Gastro-intestinal strongylosis of cattle; Its occurrence; Itssymptoms;Post-mortemappearance in gastro-intestinal strongylosis, Development, etiology, con-

trol, and treatment of gastro-intestinal strongylosis.

CHAPTER XXIII

Nematoda; SubfamilyIII. Strongylinvb; WormsoftheLargeand Small

Intestines; Other Strongyles 280

Nodu-lar strongylosis of the hog; Strongylosis of the large intestine of thesheepand

symp-toms; Itspost-mortemappearance; Intestinal strongylosis of thedog andcat; Other Strongyhnae; Tracheal strongylosis of chickens; The kidney

wormof the hog; FamilyEustrongylidseandeustrongylosis.

CHAPTER XXIV

Nematoda; FamilyVII. TbichinelliD/E 299

intestine; Trichinella spiralis and trichinosis; Life history of Trichinella spiralis; Intestinal trichinosis; Muscular trichinosis; Degeneration of the

trichina cyst; Infection;Symptomsof intestinaland musculartrichinosis in

TheThorn-headedWorm;TheLeeches 306

the intestines of the hog; Its life history; Its occurrence; Its pathogenicity;

SjTnptoms produced; Treatment; Characteristics of the class Annelida;

leech; Sources of infestation by leeches; Their effect upon theanimal

CONTENTS xiiiPART III

THE PATHOGENIQ PROTOZOA

PAGE

General consideration of the Protozoa; Characters differentiating

Classification ofpathogenicspecies.

CHAPTER XXVII TheProtozoan Subgroups;DiseasesDuetoProtozoa 324

Char-acteristics of the order Trypanosomatida; Parasitism; Transmission of

the infecting organisms;Naganaor "fly disease;" Surra, Maide Caderas;

Dourine; Trypanosoma americanum; Characteristics of the classSporozoa;

Reddysenteryof cattle;Eimeria avium;Coccidial enteritis of chicks;

Char-acteristics of the orderHemosporidia; Piroplasma bigeminum;Texas-fever

of cattle; Its occurrence; Exposure and development; Itssymptoms; The

LIST OF ILLUSTRATIONS

4. Mouth parts of a biting insect 17

6. Abdomen of locust, showing spiracles 18

7. Head of bee, showing compound eyes, ocelh, and antennae 19

8. Metamorphosis of the house fly 19

10. Eggs and larvae, of Culex mosquito 24

11. Pupa, of Culex and Anopheles mosquitoes 26

12. Culex pungens, male and female 27

13. Anopheles quadrimaculatus, male and female 28

14. Position of Anopheles and Culex at rest 28

15. Breathing position of larva, of Anopheles and Culex 29

16. Eggs of Anophelfes • 30

17. The Southern b|tfalo gnat 32

18. Larva of Southern buffalo gnat 33

19. Pupa of Southern buffalo gnat 33

20. The black horsefly 36

21. The green-head fly 36

25. The "sheep tick." 47

26. The screw worm fly 51

27. Metamorphosis of the flesh fly 52

28. Horse botfly, showing eggs, larva, and adult 54

29. Ox botfly, Hypoderma hneata, 58

30. Ox botfly, Hypoderma bovis 59

32. Larval stages of Hypoderma hneata 61

33. The sheep botfly, showing larva, pupa, and adult 63

34. The dog flea, anterior portion of body 66

35. The human flea, anterior portion of body 66

36. The dog flea, showing development and mouth-parts 67

x^i LIST OF ILLUSTRATIONS

39. Biting louse of horse, Trichodectes parumpilosus 73

40. Sucking louse of cattle,Hjematopinus eurysternus 74

41. Sucking louse of calves, Linognathus (Hsematopinus) vituli 75

42. Biting louse of cattle, Trichodectes scalaris 75

43. Sucking louse of sheep, Linognathus (Hsematopinus) pedalis . 76

44. Biting louse of sheep, Trichodectes sphaerocephalus 77

45. Sucking louse of hog, Hsematopinus suis 78

46. Sucking louse of dog, Linognathus (Hsematopinus) pihferus 78

47. Biting louse of dog, Trichodectes latus 79

48. Louse of the cat, Trichodectes subrostratus 79

49. Louse of chicken, Goniocotes gigas (G. abdominalis) 83

50. Louse of chicken, Lipeurus caponis (L variabilis) 83

51. Louse of chicken, Menopum trigonocephalum (Menoponpallidum) 83

52. Louse of turkey, Goniodes stylifer 85

53. Louse of turkey, Lipeurus meleagridis (L polytrapezius) 85

54. Louse of turkey, Menopum (Menopon) biseriatum 85

55. Louse of duck, Lipeuris anatis (L squalidus) 85

56. Louse of ducks and geese, Trinotum (Trinoton) luridum 87

57. Louse of swan, Philopterus (Docophorus) cygni 87

58. Louse of swan, Ornithonomus (Ornithobius) cygni 87

69. Louse of pigeon, Goniocotes compar '.

87

60. Louse of pigeon, Gonio.des damicornis . 87

61. Bedbug, adult female, mouth-parts etc 91

65. Mange mite burrow in human skin 105

66. Colts affectedwith sarcoptic mange 106

67. Leg scab mite of horse • , ^^'^

71 Mange mite of cat and rabbit 118

72. Auricular scab mite of rabbit 118

73. Portable dipping vat for sheep 127

77. Capitulum, scutum, and fore leg of Texas fever tick 137

78. Stigmal plates of ticks Margaropus, Ixodes, and Dermacentor . 138

78a. Photomicrograph of stigmal plate of Texas fever tick 138

79. Fowl tick, adult andlarva 139

LIST OF ILLUSTRATIONS xvii

81. The castor-bean tick 143

82. The American dog or wood tick 144

83. Linguatula rhinaria 153

84. Planarian worm 156

So. Liver fluke, Fasciola hepatica 157

86. Reproductive organs of liver fluke 158

87. Fasciola hepatica, F. americanus, Dicrocoehum lanceatum 161

89. Blood fluke, male and female IBS

92. Tapeworm of cattle and sheep, Moniezia expansa 176

93. Fringed tapeworm of sheep, anterior segments 177

94. Tapeworm of dog, Dipylidium caninum 180

96. Egg packet and Cysticercoid of Dipyhdium caninum 180

97. Tapeworm of dog. Taenia hydatigena 180

98. Tapeworm of dog. Taenia pisiformis 180

99. Tapeworm of dog, Echinococcus granulosus 180

101. Diphyllobothrium latum 186

102. Tapeworm of chicken, Choanotsenia infundibuUformis 189

103. Scolex of Choanotsenia infundibuUformis 190

104. Scolex of Davainea tetragona of chicken 190

105. Scolex of Davainea echinobothrida of chicken 190

106. Tapeworm ofman Taenia saginata 196

110. Eggs of Taenia saginata and T solium 200

112. Stages in tapeworm development 201

113. Portions of adult gid tapeworm, Multiceps multiceps 205

114. Diagrammatic section of Multiceps (Ccenurus) cyst 206

115. Brainoflamb,showingfurrowsproducedbyyounggidbladderworm 206

116. Gid bladderwonn, showing unmature tapeworm heads 206

118. Echinococcusgranulosus,showinghydatidwithbroodcapsules 214

119. Transection ofAscaris eqxii 217

120. Posterior extremity of male nematode worm 218

122. Oxyuris equi 236

xAiii LIST OF ILLUSTRATIONS

124. Egg of Ascaris lumbricoides 240

125. Ascaris lumbricoides, male and female 240

126. Heterakisperspicillmn,male andfemale,andH.vesicularis of poultry. 242

130. Lungwormofsheepandgoat,Dictyocaulusfilaria,male, female, and

132. Lung worm of cattle, Dictyocaulus viviparous 259

133. Lungwormof pig,Metastrongylusapri,male andfemale 260

134. Stomach worm of sheep, goat, and cattle, Hsemonchus contortus,

135. Hsemonchus contortus, anterior portion of body 269

136. Hsemonchuscontortus,enlargedposteriorextremityofmale 269

137. Cooperia curticei, male and female 270

138. Cooperia curticei, enlarged anterior portion 270

140. Trichostrongylus instabilis, male and female 271

142. Ostertagiaostertagi, posteriorextremityofmaleenlarged 273

143. NematodirusfilicoUis,male andfemaleandenlargedanteriorportion . 274

144. Cooperia oncophora, male and female 274

145. (Esophagostomum columbianum, male and female 282

146. (Esophagostomum columbianum,enlarged anteriorportion 282

147. (Esophagostomum columbianum, enlarged bursa of male 283

148. (Esophagostomum venulosum, male and female 283

149. (Esophagostomumvenulosum, enlargedanteriorportion 283

150. (Esophagostomum venulosum,enlargedbursaofmale 283

151. (Esophagostomum radiatum, male and female 286

152. (Esophagostomumradiatum, enlargedanteriorportion 286

153. (Esophagostomumradiatum, enlarged bursa ofmale 286

154. Chabertia ovina, male and female 287

155. Strongylus equinus, male and female 288

158. Tracheal worm of poultry, Syngamus trachealis, male and female . 294

159. Dioctophyme renale, male 297

LIST OF ILLUSTRATIONS xix

165. The thorn-headed worm, Gigantorhynchushirudinaceus 307

166. Cephalic extremity of thorn-headed worm 307

167. The horse leech 308

I. Texasfever tick,maleandfemale,with details 146

II. Texasfever tick, stages ofengorgementand details 147

III. Evolutionoftheparasite ofkala-azar 317

V Variousspecies ofTrypanosoma 331

VI Percheronstallion beforeand afterdevelopmentofdourine 338

VII Percheron mares, showingchronic dourineandlast stage 340

VIII CoccidianUfe cycle 344

TABLES

Summaryonnonparasitic,periodsindevelopmentofTexasfever tick 149

Summaryonparasitic periods indevelopment ofTexas fever tick 150

Synopsisoftapewormlarvse 194

PARASITES AND PARASITOSIS OF THE

DOMESTIC ANIMALS

PARASITES AND PARASITOSIS OF THE

DOMESTIC ANIMALS

PART IPRELIMINARY CHAPTERS

CHAPTER I

INTRODUCTION

Theearth'svast laboratoryof livingmatterincludesafloraand fauna

topographic and cHmaticvariations renderingcertain localities more or

lessinhospitabletosomeorganisms, while othersmaybe uninfluencedor

one another; this may be relatively harmonious or there may be an

intenserivalryin which organismsencroachorpreyoneupontheother,

progres-sivelydwarfed, or ultimately becoming extinct. Though most of these

inhibitive influences arenot apparent to cursory observation, theyare,

nevertheless,numerous andvariedas well as constantin theiroperation,

constitutingaprimefactor inthe evolutionandspecializationoforganicforms

the seekingof shelterfromtheconflictinachangedandoftendegenerate

ar-boreal,oreven anaquatic or semiaquatic,existence Adefenselesslittle

member of the Insectivora burrows and becomes subterranean, while

ofcaves or rock crevices, and weoftenfind creatures, usuallysomewhatdegenerate, inplaces which seem to us quite unfavorableto their sup-

and

2 PARASITES OF THE DOMESTIC ANIMALS

dependent, often solitary existence, onthe other hand, a communion of

surmised, is founded upon some mutual advantage in the strife. To

such association the general term symbiosis has been applied and each

of the organisms concernedis referred to asa symbiont Thoughthere

isby nomeansa uniformityin the appHcation oftermsreferring tothesymbioticrelationship, a usageis adoptedhere that seems bestdefined,

mu-tualism, (2) commensahsm, and (3) parasitism In the first there is a

reciprocal advantage derived from the union; in the second but one

third division onereceives an advantagetothe detriment ofthe animal

orplantwhichitinvades Thereis, however, nosharplineof

to determine in some cases whether one or both symbionts receivesbenefit from theunion, orwhether oneisorisnotinjured byit.

One of the more obvious examples of mutualism is the case of the

the whelk, for itshabitation, fromtheopeningofwhichit projectsonlyitsheadand claws Onthesurface oftheshellmayoftenbe founda seaanemone fastenednear the opening withitsmouth and tentacles in the

vicinity ofthe crab'shead The anemonein this position not onlyina

creature that would prey upon the crab must first reckon with the

bythe craband aidedin thiswayin obtainingitsfood

Such associations are not always ofmutual advantage, and may be more in the nature of an invasion of one animal upon or within thebody of another, the invading animal alone derivingbenefit, while theanimal upon which the association is forced, though not benefiting,

oyster Theoysterisnotharmed byits presence, butthe crabis

speciesofRemora,orsuckfishes, which havethefirstdorsalfinmodified

intoa suckingdiskontopofthe head By meansof thisdiskitattachesitselftoashark or otherlarge fish,andisthus carriedabout, detachingitself onlyto secure food Its benefitfrom such associationis inbeing

carried to new feeding-grounds without effort of its own, and in the

shelter fromits enemies which the body of the largerfish may afford.

The host, on the other hand, cannot be benefited, nor does itseem to

by

INTRODUCTION 3Whether this relationship between different species is of reciprocal

or atthe expenseofitsco-symbiont, and neitherhas entirelyrenounced

itsindependence Intrueparasitism the invadinganimallivesuponthe

tissues of its host, deprives it of a portion of itsnourishment; or is in

otherways injurious to it. There are many examples of this form of

symbiosis, and students of animal life are familiar with the conditions

modifications occurringin theparasite

It is the common habit ofmany animals, however, to preyupon thebodies ofother animals, and we should distinguish, so far as we may,

or chasingtheir prey, whilethelatter,in fullyacquired parasitism, live

on orinthe bodiesof theirvictims, oftenburrowingintoand consuming

faculties of specialsense andprowess, sohighly developed in predatoryanimals,becomedegenerate andatrophied

Parasitism is foimd throughout the range of animal life from the

unicellular to the vertebrate, and, though a sharp distinction between

predaceous and parasitic animalsmaynot be made, in view ofthe grading influence of the parasitic habit, the difference between the

de-simplicity ofdegenerationandthesimplicity ofprimitivenessshould be

clearlydefined In the developmentof a primitively simple animaltheyoung stages are more simplethan in the adult and ithas only simple

ancestors In the degenerate animal,onthe other hand, the ancestorsare

oftenmore complexandtheyoungstages are ofa higher gradethanthestage oftheadult The adoption of any modeof life which withdraws

bringaboutthisconditionofdegradation Ofthiswehavearemarkable

aberrant animals,inthe stageofthefree-swimminglarva,havea chordal

before they reach inaturity After passing the "tadpole" stage there

followsan extremespecialization tothefixedhabitwhichmosttunicates

retainthroughouttheiradultlife, becomingwhatare commonly known

whendisturbed,and from whichallchordatefeatureshave beenentirely

lost.

Thedegenerative changeswhich aparasite undergoes concernmostly

whileofthe sense-organs nothingmaybeleftexcept thoseoftouch The

4 PARASITES OF THE DOMESTIC ANIMALS

clasping the hairs of the host, or itmay almost if not completely

the contents of the alimentary canal or tissue fluids of the host upon

thedigestive organsbecomesimplifiedormay bequite lost, the

absorb-tion ofnutriment in the latter case taking place entirely through thebodyintegument,as insomeofthe wormswhichinfesttheintestines of

manand other animals The degreeof decadencewilldependupon thedegreeofdependenceuponthehost: Inthislatterrespectthe parasitism

maybeoptional, asinthe case ofthemosquito,whichmayliveuponthe

juicesofplantsbutprefersamealofwarm blood, oritmaybe obligate,

obligate parasites as the biting flies, fleas, and bedbugs may also live

free and only occasionly visit their hosts, a forin of parasitism which

life.

In theeventoftheparasitebecomingprogressivelydegradedintoone

itfor bothits nutrition and place ofabode, all oftheabove mentioned

phenomenaofadaptationbecome moreconspicuous Thereisfurnished

occasional visitor, has, like the louse, taken permanent abode upon its

host No longer taking the aerial flight of its discarded free life, this

fly hasbecome wingless, and, furthermore, is enabled to pass its entire

life cycleupon the bodyofthe hostanimal bya remarkablemethod of

reproduction involving the retention of the eggs in the oviducts until

passinto the stage ofthe pupa that thelarvae are extruded, the pupal

casethen beingattached to the individual woolfibers. From this case

the younginsect, on becoming sufficientlydeveloped, makes its escape

and proceedsto feed and grow, thus rounding out a complete parasiticcycle

perpetua-tionofthespeciesbecomesmoreprecarious,andthe organsof

parasites, especially those existing in the interior of its body, die with

it,and,wereitnot that the eggsfindlodgnientinanewhost,theparasiticspecieswouldina shorttime becomeextinct Thetransmission ofbut

fewofthese eggsissuccessfullyaccomplished, andincompensation they

elements ofdestruction which theyencounter The modeof

reproduc-tion is one ofthe principal factors determining the conditions of

INTRODUCTION 5dwelling continuouslyupon orwithin the bodies of their hosts, we have

inthe ffistridse, among the dipterous insects, a cycleinvolvinginternal

parasitism during thelarval stage,afamiliarexamplebeing thecommon

horse botfly (Gastrophilus intestinalis) , the development of which isgiven on page 54 It is plain that a very small percentage of theeggsdeposited bythisflycan reach the horse'smouth, and that,having got

the intestinal tract without having succeeded in becomingfixed to themucous membrane. For this there seems to be compensation in the

largenumber of eggs depositedbythepersistent female

onehost, often, for reasons stated in theforegoing, two successive and

generally specifically different hosts are required A rather cated example ofthelatter case isthelife history of the commonliver

compli-fluke (Fasciola hepatica), one of the flat worms infesting in its adult

statethe hversofHerbivora It willbe notedinreferringtothecycle ofthis parasite, given in detail elsewhere (page 160), that it is a very

co-operation of numerous favorable conditions The eggs, of which each

individual fluke is capable of producing in the neighborhood of one

to theirhatching Ifhatched, the larva mustescape its many aquatic

when it is again liable to fall prey to various small aquatic animals

theenormous numberof eggs, and thenumberof individualswhich oneeggmayproduce, tothiesurvival ofthe speciesamid conditionsfraught

In generalitmaybe saidas tothepropagationof parasitesthattheir

prodigious fecundity and the greatvital resistance with whichmost of

them are endowed enables speciesto survive and perpetuate theirkindamid varied destro3dng influences which otherwise would bring about

their extermination The tapeworms inhabiting the intestines of man

andother animals, affordanotherexampleofextremeparasitism

accom-panied by this remarkable development of the reproductive function

Hereis a creature so altered to its degenerate existencethat it has

be-come devoid ofmouth and intestine, the body consisting of a scolex,

usuallyreferredto asthe head, from whichare giveoffsegments which

6 PARASITES OF THE DOMESTIC ANIMALS

exceed twenty feet. After about the six hundredth, each segment is a

eggs Bythesuccessivedetachmentofthese"ripe" segmentsandtheir

passage from the body of the host, it has been estimated that Taenia

saginata might throw off in a year as many as one hundred and fifty

million eggs, of which but aninfinitesimal number, asisquite evident,

will reach the bodyof their proper bovine hostforlarval development

Again, having been so fortunate, it is improbable that the larvae will,while living, reach the intestines ofthe human host necessary for their

further development into adultworms

Here, then, is an animal well showing the degree of degeneration

locomotion, noorgansof specialsense,no organsof digestion, no organs

of respiration, andnoneoftruecirculation. The bodyconsists ofalongband of connected segments, each, when mature, bisexually complete

and in itself a sort of independent reproductive individual, the entire

that the perpetuationofthespeciesmaybe insuredamidthe perilswith

In many forms permanently parasitic there is an early period of

assumedthatthisgradualloss oforgans, changeof structure,andtive transmission of the embryo to an intermediate host is due to the

protec-parasitic life, it seems reasonable to conclude that all of the parasitic

becameamorefixedhabit,suchstructuralchangeswereinthe courseof

re-view of the observed facts, then, in their biologic relationship, leads to

the conclusion that symbiosis, of which parasitism is a form, has itscausativebasis inthe struggleforexistence,the symbioticassociationin

It further follows that, thoughsome formshave vmdergone an extreme

modification, through related contemporaryfree-livingtypes, theirtruesystematic positionmaybe established

chapterswhichareto follow Thosebelowarenot givenwiththe

their definitions;moreessentialissuchanunderstanding that examplescanreadilybepickedout,atypical illustrationalwaysbeinginmindfor

application to the term at hand With such a conception the studentshouldbeable to formulatehisowndefinitions, andthiswillbeofmore

con-ceptionsofanother

Though someofthefollowingtermshave beentreated of inforegoingintroductory remarks,theyare here includedformore concise definition

two animals, or an animal and a plant, the union being in a measure

beneficialtoboth,or toone withorwithoutharmtotheother

Mutualism is a form of symbiosis in which both symbionts are in

Comanensalismis thatform ofsymbiosisinwhich but one symbiont

is benefited, while its co-symbiont is neither benefited nor harmed bythe union

enslavetheother, enforcingittolaborinitsbehalf Thetermisapplied

to such association in certain insects.

Parasitismis that formof symbiosis inwhich one symbiont,forposes of procuring food, or food and shelter, visits briefly, or takes up

host

Phytoparasites are parasites which belong with the vegetable

8 PARASITES OF THE DOMESTIC ANIMALS

Zobparasites are parasites which belong withthe animalkingdom

Optional Occasional Parasites are those which only fleetingly visit

theirhoststoobtain nourishment, butarenotdependentupon themforeithernourishmentorshelter. Example, mosquitoes

Obligate Occasional Parasites are those which do not permanentlyliveupontheir hosts, butare dependentupon themfornourishmentand

tosome extentfor shelter. Examples, fleas, bedbugs

islimited toadefinite phaseorphasesintheirlifehistory,duringwhich

time the parasitism is obligate and continuous Examples, botflies, ticks.

PermanentParasitesarethoseinwhichthe parasitism extendsfrom

thehatchingoftheeggtothestage ofreproductioninthe adult

one host to another Examples, larvse of botflies, Linguatula,

helmin-thes.

Erratic Parasites are those which in their adult state may pass

readily from one host to another of the same or different and widelyseparatedspecies. Examples,mosquitoes, bitingflies, ticks, leeches

hosttoanotherofthesamespecies, ora species closelyalliedto theone

by the host, the embr3'^os, while still within the eggs, passing to anew

Ascaris

conditions of moisture and temperature, but cannot undergo further

Hemonchus contortus.

hostby anintermediateor transitory host, inwhich they cannot attaintheir complete development; consequently, a reciprocal transmission

the parasite Examples, tapeworms, Plasmodiumofmalaria

(b) The eggsof the parasite are hatchedinthebodyof thehost, the

at-tainingthe adultstate untiltheyhavereached a secondhost Example,

Trichinella spiralis.

parasitesfrom one host to another

Incidental or Stray Parasites are those which under natural

condi-FORMS OF PARASITISM 9chus hirudinaceus (specific in pig, incidental in man); Fasciola hepatica

Ectoparasites (Epizoa) are those which are parasitic to the surface

onlyoccasionalvisitors. Examples,scabmites,ticks,andotherAcarina,lice, flies. All ofthe arthropodalparasiteswithscarcelyan exception

host, inhabiting itsalimentary canal, blood; and other tissues.

Helminthes is a term under which are grouped all of the worms

generally parasitic, with the exception of a small number inwhich thebody is annulated The group is not a natural zoological one and is

thename ofthe genus, or other group name to which the parasite longs, as theroot, to which is added the suffix asis or osis. As for ex-

be-ample:

Pediculosis, the condition produced by the presence of lice uponthe skin; Acariasis, the condition produced by the presence upon the

skin of mites and otherAcarina; Filariasis, the condition produced by

Oxyuris, Strongylosis from Strongylidse, Trichinosis from Trichinella,Taeniasisfrom Taeniidse, Fascioliasis from Fasciola, Helminthiasisfrom

Helminthes,and Trypanosomiasis fromTrypanosoma

In view of the many factors to be considered, the formulation of

exact and limiting interpretations of terms bearing upon kinds of

par-asitism is scarcely possible It cannot be claimed for the above series,

therefore, thatit isentirelysatisfactory as stated anddefined For our

conceptionswe must relyupon thebehavior of thetypical ratherthan

the isolated or synthetic, and be content to regard anygrouping based

upon modes ofparasitismasmoreconvenientthanexact It is difficult

to circumscribe parasitism; whilewe speak of the parasiticmode oflife

asaformofsymbiosis, itmaywellbequestionedwhethersuchinsects as

hosts; theirfleeting visitscertainlydonotconstitute theliving together

as usuallyimpKed by the term Again, we maynot be able to draw a

distinct line between certain predaceous and certain parasitic forms

Fromthemoregeneral viewpoint, however, itmay berepeated that all

and cunning, seizeupon and aim to destroy theirpreyat once, feedingupon the body There are parasites which use a degree of stealth in

.invasion ofthebody ofitsvictim bythe parasite ismore oftenpassive

10 PARASITES OF THE DOMESTIC ANIMALS

the parasite's welfare to destroy its host To destroy the body of the

subsistence as well as in most casesits shelter. When the host animal

diesitsinternal parasites diewithit,and,if itwerenotforthe previouslyoccurring transmissionof their offspring to newhosts,the specieswouldrapidly perish. Serious disturbance or death of the host due to its

parasites is usuallybrought about by theirpresence in large numbers,

at once destroyed and whollyor inpart devoured

Theparasite isalways smaller and weaker thanitshost,andinmany

cases itsinfluenceupon the latter isnotobservable Itmaybe said in

general that the degree of injury will depend upon the following cipal factors

prin-Influence Upon the Host

1. The Number of Parasites Present.— A tapeworm or one or two

ascarids in the intestinesmay notproduce anoticeable effectupon the

host Ifthese parasites arenumeroustheremaybeseriousdisturbances

in the host resultingfromthe deprivationof nutrimentwhich hasbeen

appropriated by theinfesting worms, fromthe toxins which they orate, oramore acuteeffectmaybebrought about through obstruction

in its usual location will do no observable harm to its host, but if itshould lodgein the eye or central nervous systemit might give rise toserious disorders As a rule, intestinal parasites are less harmful than

those which invade the blood orrespiratory tract, while ofthe externalparasites, those which burrow into the integument are more injurious

than thoselivingupon thesurface

tissues of its host ismore harmful than onewhich merely appropriates

a share of the latter's ingested nutriment The blood-sucking worms,

when present in considerable numbers, bring about serious depletivedisturbances, while suchwormsasthe adultascarids,nourishingmainly

upontheresidue offoodmaterials,are,ingeneral,lessharmful Sucking

lice, armedwithpiercingmouthparts,aremoredisturbing totheanimal

harboring them than the biting lice which feed upon cutaneous d6bris

andthe products of theirirritation.

INFLUENCE UPON THE HOST 11

typical instance An otherwise relatively harmless parasite may work

its way into a duct, or, finding lodgment in an unusual organ, set up

wandering, fistulous communications may be established between

contiguousorgans normallypossessingno direct connection

5. Age of Host.— Young animals are predisposed to endoparasitic

invasion To forms which penetrateor are more orless migratory, themore tender tissues of the young offer less resistance than in older

animals Verminousbronchitisisaformof strongylosisobservedalmost

exclusively in animals which are immature The reduced vitality ofold age invites the iavasion of both external and internal parasites;

there isnot only a lessened ability to defend from attack, but reduced

de-creasethe capability ofeliminating eitherecto- orentozoa

Suchexternal parasites asmosquitoes, flies, ticks, and bedbugsare ofgreatest pathologic importance as disseminators of infectious diseases,

acting either as direct carriers or as intermediateor definitive hosts of

the infecting organism Malaria, Texas fever, and forms of osomiasisare amongdiseaseswhichareknowntobespread onlybythis

infections engendered by the habits of the common house fly are well

known

that, in cases of heavy infestation especially, this toxic effect must be

considerably contributed to by the products of decomposition of deadworms

Etiology.—So varied are the conditions that surround the

propaga-tion and existence of parasites that the consideration of the causes ofparasitic diseasesisbestembodiedinchaptersdevotedto their particularoccurrence However, certain circumstances favoring parasitism may

beherebriefly considered

Crowded and imclean housing favors the propagation and spread ofparasites ofboth man and domestic animals For this reason lice andscabmitesfind theirmostfavorable season inthe winter months, when

their transmissionfrom animalto animal is facilitated and the reduced

and the scab acariases are seldom seen, however, in stables that arewellkept, oramonganimalswhere dueattentionispaidto cleanliness of

adult parasitic Diptera, and it is during the months at pasture that

ticksmostrapidlypropagate and crawlupon their hosts

environment

12 PARASITES OF THE DOMESTIC ANIMALS

are more subordinate to the mode of development of the infecting

present conditions essential tothemoUuscanintermediate hostinwhich

theflukeatthe stageofthemiracidiummustfindlodgment Infestation

of the pig or the ox with the larvae of the tapeworms ofman is most

with such material, while invasion of the human host with the adult

worm only occurs afteringestion of'the tissues of thelarval host The

majorityof ovaofwormsexpelled bythe hostfail to findanewhost, or

meet with unfavorable conditions and are lost. Some, as those ofascarids, areveryresistantandmayfind theirproper hostaftermonths

of exposure to destructive infiuences Migration is facilitated to someextent wherehatching takesplace with the laying ofthe egg, as in the

strongyles ofthe respiratory tractand in Trichinella

of the internal parasites, clinical experience indicates that low and wet

pasturage, with access to stagnant collections of water, is a strong

intermediate hosts of the worms, or as a vehicle which, directly or by

drainage, spreadsinfestationby dissemination of theirgerms

CHAPTER III

PHYLUM I. AETHROPODA

accordingto their location, as thoseof theskin, those oftheintestines,

those ofthe liver, those of the circulation, etc., the fact that so many

intheirlifehistoriespasscertainstages iadifferent organsanddifferentspecies of hosts makes such an arrangement somewhat confus.ed It

intheparasite'sorder, essentiallyincludingsuch anatomicaland

zoolog-icalmigrations asmaybeinvolved, whileat thesame time consideringitspathogenicinfluences inthese varyinglocations

Asidefrom the phytoparasites, which are not includedin this work,theparasites infestingman anddomestic animalsare distributedamong

of their zoologicalgrade,areProtozoa,Platyhelminthes, Coelhelminthes,andArthropoda Thelastnamedgroupcontainsmostalloftheexternalparasitesandisthefirsttobe consideredinthepagesto follow

As a foundation for the scientific control of parasitism and for therecognition of adaptations to its various forms, at least an elementary

subdivisions to which the parasite belongs is of essential importance

ofthe differentgroupsand theirsubgroups isbased willbe givenhere

For moredetailedstudythestudentisreferredtoan advancedtext-book

in zoology

The phylumArthropodaincludessuch animals asthecrayfish, crabs,

hard or leathery external chitinous skeleton divided into a number of

adult, or a certainnimiberofthe segments, bearingjointedappendages

specialmodification ofthe constituantsegments In order that ments may take place between the segments of both the body properand ofthe appendages, the cuticle at these points is thin and delicate

heavierchitinous armor

All arthropodsperiodicallymolt, the process consisting oftheand

break-14 PARASITES OF THE DOMESTIC ANIMALS

underlyingtissueand anewcuticle has beenformed Whilethe cuticle

isat first thinand soft, later itbecomes hard and unyielding, therefore

the moltings are necessaryfor the accommodationof growthandoccur

periodically as long as this growth continues Chitin, to which thefirmness of the cuticular exoskeleton is due, is an organic substance in

skinis never ciliated, nor do ciliated cells occur in anyother organs of

the body

muscles passing from one segment to another and attached at theirextremities tothe innersideoftheskin,theircontractionbringingabout

movements of the segments of the body and appendages oneupon the

other They may be attached by so-called tendons, which consist of

invaginationsofthe cuticle surrounded bya corresponding invagination

ofthe epidermis Themusclefibers are striated and multinuclear.The digestive tract (Fig. 2) passes directly, or with little flexion,

ventral, the anus posterior Accessory organs, as salivary glands and

liver, may ormay not bepresent

Ofthe circulatorysystem (Figs. 2and3) themostconstant portionistheheart,whichisusuallytubularandlocated dorsally Oneachside of

the organ are openings provided with valves through which the bloodpasses tobe propelledforward From thelarge arteriesthe blood may

passdirectlyiatoblood sinuses, oritmaycoursethroughcapillaries and

veins, thoughthe vascularsystemisneverentirelyclosed. Thebloodisusuallya colorless fluidwith colorless amoeboid corpuscles

In aquatic forms (Crustacea) respiration isby gills, while in the

air-breathers it may be bytracheae (Figs. 5 and 6), consisting oftubular

ramifications fromwithout towithin thebody, orbypeculiar infolding

modifications of the integumentfunctioning as lungs In some of thelowerforms respiratoryorgans are entirely absent,the function in such

casesbeing diffused over theentire bodysurface

In various spaces within the bodies of Arthropoda are frequently

fat, serve as a store ofnourishment The fact that products of tissue

metabolism, suchas uricacid, have been foundinthe fatbody,leads to

the conclusion that it also acts as a place of storage for substances ofexcretionbefore their elimination bythe excretoryorgans, which latter

greatly vary in the different groups In insects and arachnids theseorgans are represented bythe Malpighian tubes, long glandular canals

connectedbya double longitudinalnerve cord In well-developed

seg-and

ARTHROPODA 15

be expected, as in the annelid worms In the Arthropoda, however,

there are differences due to fusion ofthe segments, in which case there

is also fusion of their ganglia Such fusion is usually accompanied by more orlessshorteningofthebody, anexample ofwhichis affordedby

the spiders and crabs where the whole ventral chain unites in a single

ganglionic mass From themost anterior of the ventral gangha therespring two nerve cords which pass on either side of the esophagus tounite above it with the paired cerebral ganglion or brain, l3ang in thehead Thisganglion remains distinct, its dorsal positionpreventingits

fusion with gangliaofthe ventral chain

Ofthe senseorgans themosthighly developedare theeyes,which are

therearebothoftheseforms,whileothers areprovided only with ocelli,

and in some arthropods eyes are absent In the compound eyes the

cuticle covering them is divided into hexagonal facets, the number of

spiders

With rare exceptions the sexes are separate, and reproduction isgenerally by fertilized eggs, though parthenogenesis occurs, in some

caseshavingacertain relationship tothelifehistory Usually thesexes

can be readily distinguished by the difference in size and by variousmodificationsofthe appendages

parasitic species of medical interest will be considered in this work

with scarcely an exception, contain all of the external parasites It is

external, as certain insects and arachnids pass a phaseof theirmentwithin the bodiesof their hosts

develop-Class I. Insecta

thelargestofallanimalgroups The bodyisessentiallysegmented, and

is divided into three regions,—^head, thorax, and abdomen, which are

distinctlymarked offfrom each other (Fig 1).

The head is usually freelymovable at its jimction with the thorax,

and typically bears on each side a compound eye (Figs 1 and 7),

Arising from the head are a pair of antennae which consist of

seg-and number

16 PARASITES OF THE DOMESTIC ANIMALS

may-be referred to a common type This is well presented in itsprimitive

condition by the grasshopper,

in front of the mouth Under

jaws, the mandibles, each

piece with acutting inner edge,

isthe firstpair of maxillaewhich

are prehensile andgustatory infunction These have a num-

ber of joints and bear curved

sec-ond pair of maxillae are fused

la-FiG 1.—DiagramofanInsect, withHeadand bium,wMchisaCCeSSOryin

antennae; b, prothorax; c, mesothorax; d,meta- lliSS, and, llKe tne latter, bear athorax; e, abdomen; f, ovipositor. The pro-, pair of Segmented palpi. The

themeso-andmetathorax each a pair of wings. i^Drnm lorms tne posterior ana

Dodge;Copyright, 1894,byHarper&Brothers). ^j^^^^^^^^ ^^.^^ ^^ ^^^ ^^^^^segments, an anterior,—the prothorax, a middle,—the mesothorax

Fig 2.—Diagram of the Principal Internal Anatomical Parts of an

Insect: m,mouth; cr, crop; st, stomach; i, lower portion of intestine;

ganglion;Mp, Malpighian tubules; o, ovaries; g, genital aperature (after

and a posterior,—^the metathorax

somewhat

The last two of these are usually

ARTHROPODA 17

femur, tibia, and tarsus The attachment to

thebodyisbytheshort coxa, to whichis joined

the trochanter which is also short. Following

the trochanter are two long segments,—the

thanthelatterandcontaining the muscles The

tarsus, or foot, follows the tibia, and consistsof

a number of short segments, the last bearing

hook-like structures, or claws

Usualty there are two pairs of wmgs arising dorsall,y from the

meso-FiG 3.—Diagram of sect's Heart: c, constriction

In-between two chambers; v, valves (after Boas, byKirk- aldy&Pollard).

Fig 4.—Mouth-parts of Locust, a biting insect: Labrum, or upper-lip,

Labium, or under lip, with labial palpi below Maxillae, or lower pair of jaws, with maxillary palpi, to right and left (from photomicrograph of

mountedspecimen, byHoedt)

18 PARASITES OF THE DOMESTIC ANIMALS

the blood sinuses and tracheae. Sometimesthe anterior, sometimes the

posterior pair is the larger, and both may be flexible and adapted for

flight. In some insects (beetles) the anterior pair is modified to form

wing-shields, or elytra, which are hard, but

and protect the posterior wings during rest.

Some insects possess but one pair of wings

(dipterous), while in others wings are entirely

absent (apterous)

The abdomen is segmented, the number of

.segments varying with differentgroups Each

the dorsal tergite and the ventral sternite,

mem-brane, the pleurite. There are no abdominal

limbsorlimb-hke appendages

Respiration is bytracheae (Fig 5), a system

of tubes containing air. These communicatewith the outside by

6), small

s}Tnmet-r i ca1 1y disposedopenings located

pair on each of the

abdominal segments

except themost posterior. Just inside ofthe spiracles thetracheae are

usually united by longitudinal trunks from which are given off fine

branches whichramify and anastomose within the body Respiration

is effected by abdominal movements of contraction and expansion

Insects are mostly oviparous In some the developed embryo is

released fromthe egg while still within the body of the parent, or this

mayoccurjustasthe eggisextruded Thereare alsopupiparousforms

In order that thenewly hatchedlarvaemaybe supplied with

In manyinsects oviposition occurs by means of an ovipositor, a

tube-like organ which is developed from the posterior abdominal segments

may

Fig 5.—Diagram

show-ing the chief trunks of the

tracheal system of an

in-sect (after Boas, by

Kirk-aldy&Pollard).

Fig 6.—^Abdomen of

Lo-cust,showingSpiracles 1, 2, 3,

of each of the abdominal

Zool-ogy).

ARTHROPODA 19

aweapon of defenseprovided with poison ii;lan(ls P'roni itsnature thestingisessentialh' onlj'possessed Ijy the females

Some insects on leaving the egg develop directly to the adult stage,

the larvainmostcasesdifferingfromthe adult

prin-cipallj' in the absence of wings In such casesthere

meta-niorphic process is not thorough, and is therefore

referred to as incomplete metamorphosis The

ma-jority of insects when hatched from the egg bear

observ-able gradual approach to this form The larva is

characteristicallyworm-likeand an active andvora- ^-^e bee, s^howing

cious feeder, a number of molts occui'ring with the compound eyes, the

increase in size during this stage There then ^^^'^'' °celli, and the

, iv 1 1 1 1 IX J antennee. —

periodofpupation, duringwhichthe animalisquies- Dodge; Copyright,

'centandaseries ofchanges

^^^tke'S

""''" *occurm the body Atthe

conclusion of these changes the pupal case

theunfoldingof the

essentialsdevelopedinto

the complete sexualadult In this form

changesaredistinct,and

the process is referred

to as complete morphosis (Fig 8).

meta-The duration of life

stages of the egg, larva,

pupa, andadult,usually

doesnot extend beyond

a year With quite anumber it is much

shorter than this, whileFig.9.-Diagram of terrai- with othersit may be a

Metamor-phosis of theHouseFly,

pupal, and adult stages.

On the right is an

glandu-lar hairs: on upper left,

a tsetse fly (from

20 PARASITES OF THE DOMESTIC ANIMALS

affordedbythe seventeen-yearcicada Mostoftheinsecthfeisoccupied

bythelarval stage,duringwhich the greatestgrowthtakesplace With

afewexceptions, ashoneybeesandants,the periodofthe adultisshort,

in some cases a few days or even hours The life of the adult is

dieswhen thisis accomplished

medicalimportance

ClassA Insecta P 15.

Genus and Species:

A punctipennis P 28.

Ades calopus P 29.

Genusand Species:

Genusand Species:

Stomoxyscalcitrans. Animals attacked, equines and cattle.

P 39.

Lyperosiairritans. Animalsattacked, cattle. P 41.

Glossina palpalis. Animals attacked, man, and domesticandwildanimals P.44.

G morsitans Animals attacked, same P 44.