A TAPEWORM 83 



Study in the same way the mature proglottids. Find the 

 uterus. It is here a straight, narrow tube in the middle of 

 the proglottid, and is not yet distended with eggs. Near the 

 center and toward the posterior end of the proglottid will be 

 seen an irregular mass of organs. These are the paired ovaries, 

 two large, round bodies, one on each side of the uterus; the 

 median yolk gland, which is below the end of the uterus, near 

 the posterior margin of the proglottid; the shell gland, between 

 the yolk gland and the uterus. From the shell gland the vagina 

 and vas deferens proceed to the genital cloaca, the former being 

 the smaller and more posterior of the two. Scattered through- 

 out the proglottid are numerous small round bodies, the testes, 

 which are joined with the vas deferens by numerous minute 

 vasa efferentia. Find the excretory canals and the longitudinal nerves. 



Exercise 5. Draw the proglottid, showing all of these features 

 you have observed ; carefully label all. 



Study in the same way the immature proglottids from the 

 forward end of the body. Find as many of the organs men- 

 tioned as are present. 



Exercise 6. Draw the immature proglottid. 



The tapeworm may fertilize itself or be fertilized by another 

 individual, and where self-fertilization takes place one proglottid 

 of the animal may fertilize another, or a single proglottid may 

 fertilize itself. The ova from the ovaries, on being fertilized, pass 

 at once into the uterus. The ripe proglottids, which are filled 

 with eggs in which the embryo has already begun to develop, 

 break off from the hinder end of the worm and pass out of the 

 body of the host. They then break open or are crushed, and 

 their eggs are scattered on all sides. 



The encysted tapeworm. The adult worm alone is found in the 

 intestine. The eggs, in order to develop, must pass out of the 

 host and fall upon something which will afterward be eaten by 



