788 General and Applied Biology 



B. Diseases of Animals Other Than Human — Cont'd 



{Echinococcus 

 granulosus) 



(3) "Staggers" or 

 gid tapeworm of 

 sheep 



{Multiceps 

 multiceps) 

 (Fig. 268) 



(b) Roundworms 



(Nemathelminthes ) 



(4) Roundworm of 

 horses {Stron- 

 gylus vulgaris) 

 (compare Figs. 

 99 to 101) 



(5) Dog ascarid 

 (Toxocara 

 canis) 



(6) "Gapes" of 

 poultry and 

 game birds 

 {Syngamus 

 trachea) 



(c) Segmented worms 

 (Annelida) 

 (7) Leeches 



(various species) 

 (Fig. 114) 



3. Diseases of Animals 

 Caused by Mollusks 

 (a) "Blackheads" or 

 black cysts of fish 

 (larv^al stage or 

 glochidium of 

 mussels) 



4. Diseases of Animals 

 Caused by Arthropods 



as hydatid cysts, may reach the size of a child's 

 head and contain thousands of daughter cysts, 

 each of which may give origin to a new worm; 

 may be quite serious in severe cases; widespread 

 in distribution; called hydatid disease in man 

 The larva, known as a coenurus (se -nu' rus) (Gr. 

 koinos, common; oura, tail), contains several 

 scoleces in each cyst, and, lodged in the brain 

 of ruminant animals, causes "staggers" or "gid"; 

 may be transmitted from dogs or other animals 



Ingested larvae from feces of horses encyst in the 

 colon or cecum of the horse where sucking of 

 blood results in anemia; world-wide distribution, 

 especially in warmer countries 



Dogs become infected by swallowing eggs, espe- 

 cially young puppies; an acquired immunity 

 results in the elimination of the worms in a few 

 months; larvae migrate through the body of the 

 dog much in the manner of Ascaris in man 



Infestation occurs by ingesting larvae from feces 

 or materials coughed up by infested birds; larvae 

 travel through the esophagus, lungs, and trachea, 

 where they attach and forms capsules, produc- 

 ing the characteristic "gapes"; abscesses may 

 form; slender, red, adults in the trachea may 

 produce eggs which develop into larvae; com- 

 mon in fowls and wild birds; may affect hu- 

 man beings in the tropics 



The fresh-water leech (Macrobdella) sucks blood 

 from man, frogs, fish, and cattle; the horse 

 leech {Haemopis) parasitizes horses, snails, 

 worms, etc., and lives in mud near fresh-water; 

 the medicinal leech {Hirudo medicinalis) sucks 

 blood from many types of vertebrate animals; 

 blood clotting is prevented by a special secre- 

 tion; may suck blood up to three times its own 

 weight and require several months to digest 



The eggs of mussels develop into bivalved, larval 

 glochidia which are cast into the water where 

 they clamp their jaws into the gills, fins, and 

 body of fish; the fish forms a black cyst around 

 the glochidium; eventually the cyst ruptures to 

 liberate the developing larva and it begins its 

 free-living existence as a young adult mussel 



The diseases of animals and plants produced by 

 members of the arthropod phylum and the dis- 

 eases transmitted by members of this group are 

 so numerous that the reader is referred to the 

 chapter on the Economic Importance of Ani- 

 mals (phylum Arthropoda) or to textbooks of 

 entomology 



