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. 
Bxercise 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 
