ANIMAL PARASITES. 



' 



.XIA MEDIOCANELLATA. HEAD AND PRO- 

 GLOTTIDES. 



A, heud X about 15. 



B, mature proglottid, showing generative apparatus. 



C, head and fragments of immature proglottides, show- 

 ing gradual tapering of the neck. Natural size. 



monly seen in the muscles of the pig as an encysted scolex, commonly 

 called a "measle." It occasionally occurs in man in the muscles, brain, 

 eye, etc., and is called cysticercus cellulosce. It is usually about the size 



of a pea, but may be as large 

 as a pigeon's egg and surround- 

 ed by a connective-tissue cap- 

 sule. 



Infection with the worm 

 occurs in the human subject 

 from the ingestion of insuf- 

 ficiently cooked "measly" 

 pork, or, in the case of cysti- 

 cercus cellulosae, from the in- 

 gestion of the eggs, which may, 

 in a variety of ways in un- 

 cleanly persons, get into the 

 food. 



Tcenia mediocanellata (T, 



FIG. ")!). T.XI A MEDIOCANELLATA. HEAD AND PRO- 8ttffi)Ult(( LEUCKART). The 



head of this species is some- 

 what cuboidal, with neither ros- 

 tellurn nor booklets, but with 

 four sucking discs (Fig. 59). 

 The segments are generally broader and shorter than in T. sol him, and 

 the worm is usually larger. In the embryonal form the scolex occurs 

 as the Cysticercus tcenice mediocanellatce in the form of small cysts in the 

 muscles of cattle, from the eating of which in the uncooked condition 

 the infection occurs. This is the most common tapeworm in the United 

 States. 



Tcenia ecMnococcus. This worm in the mature condition forms a 

 short, small colony inhabiting the intestine of the dog. The head is 

 about 0.3 mm. in diameter and 

 has a double row of hooklets 

 around the rostellum. The pro- 

 glottides are three or four in 

 number, the last being the larger. 

 The entire colony is not more 

 than 4 to 5 mm. in length. 

 The significance of this parasite 

 in human pathology depends 

 upon the cysts, called hydatids, 

 which it forms, in the immature 

 or cysticercus stage, in various parts of the body. Intimate associa- 

 tion with dogs favors the acquirement of this parasite. \\Tien the eggs 

 of the mature worm get into the intestinal canal of man they undergo 

 partial development and find their way into the tissues and organs, 

 most frequently into the liver. Here cysts are formed which become 



FIG. 60. CCTICULA or ECHINOCOCCCS CYST. 

 Showing lamellated structure. 



