68 PHYLUM VERMES 



The tapeworm may fertilize itself or be fertilized by another 

 individual, and where self-fertilization takes place one proglottid 

 of the anunal 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 

 another animal, called the intermediate host, which is itself 

 preyed upon by the host. After being thus transferred to the 

 stomach of the intermediate host, there hatches from each egg a 

 minute, spherical embryo, called the six-hooked embryo, which is 

 provided with three pairs of hooklike organs of locomotion. This 

 embryo works its way through the wall of the intestine of the 

 animal and migrates finally to some one of the internal organs, 

 where it lodges and grows into a cystlike larval form, called the 

 cysticercus. Within the cysticercus is a fully developed scolex, 

 but turned wrong side out. If now the intermediate host is 

 eaten by the host, the scolex turns right side out, passes into the 

 intestine of the latter, attaches itself to the intestmal wall, and 

 grows into an adult tapeworm. 



The intermediate host of TcBuia saginata is the beef, in the 

 muscles of which the cysticercus will be found, if present. That 

 of Tcenia serrata is the rabbit and that of Tcenia crassicollis is 

 the mouse; in the former animal the cysticerci are embedded 

 in the peritoneum or the liver, and in the latter, in the liver. 

 Open the body cavity of either of these animals by a median 

 ventral incision and look for cysticerci. They are large, whitish 

 bodies and are easily detected if present. When a cysticercus is 

 found, it should be carefully dissected out, its outer wall slit and 

 the scolex exposed to view. Mount it on a slide in dilute glyceruie 

 and study it. 

 Exercise 7, Draw a view of the scolex in its cyst> 



