ANIMAL PARASITES 



31 



mammals, including man. The adult is a very small worm living 

 in the intestine of dogs. It measures a fourth of an inch or less 

 in length and has but three proglottides. The head is very small, 

 with a prominent rostellum armed with a double row of hooks. 

 The terminal, ripe proglottis comprises about half the entire 

 length of the worm but contains a relatively small number of 

 eggs. 



Fig. 12. — A section of the cyst of Echinococcus granulosus in the liver of a pig. 

 A, brood capsule; B, scolex; C, germinal layer; D, cuticle; E, adventitious layer, 

 formed by the host. The three layers have been separated in the process of 

 sectioning. {Orig.) 



The cysts develop slowly in the intermediate host but in 

 man may attain the size of an orange or even of a human head. 

 The thick wall of the cyst is composed of an outer adventitious 

 layer formed by connective tissue of the host. Next is a firm 

 lamellated layer called the cuticular membrane. Within this is 

 the thin germinal layer. From the germinal layer and from cer- 

 tain scolices which undergo metamorphosis, there are formed 

 many brood capsules within which arise numerous larval scolices. 

 Thousands of these potential tapeworms may be present in 



