GENERAL PRINCIPLES 



so much in the adult stage as in the cysticercus. This, embedded 

 in the brain or other organs of the body, sometimes reaches 

 enormous size and destroys the surrounding tissues of the host. 

 756. As internal parasites the threadworms are very common. 

 The famous "horsehair snake" (Gordius) is a parasite in the 



FIG. 234. Sexually mature proglottis of Taenia. ov, Ovaries; rs, receptaculum 

 seminis; sg, shell gland; t, testis; v, vagina; vd, vas deferens; yg, yolk gland. 

 Other letters as in preceding figure. (From Galloway.) 



cricket during the later developmental stages. At maturity it 

 is free, living in the water. 



757. Trichinella spiralis is the parasite which often infests 

 the flesh of swine and is frequently transmitted to man by the 

 eating of uncooked pork. The adult worm is 3-4 mm. long, 

 and bores into the wall of the intestine, where the young are 

 produced in large numbers. The young are only .1 mm. long, 



