THE CGELOMATA INVERTEBRATA 



201 



to Eastern countries, where it is common. The head is oval, and 

 possesses only two lateral deep groove-like suckers. It has two 

 external openings on the proglottid, one the ordinary genital pore, 

 and the other that of the much curved uterus. The cysticercus is 

 passed in the muscles of some fresh-water fish. 



Dipylidium caninum is a small form, 35 c.m. in length, only 

 rarely found in human beings, but is interesting because the genital 

 organs are duplicated in each proglottid, each set opening by a 



t-G. 



FIG. 65. Proglottids of A, Tcenia saginata, ripe; B, Dibothno- 

 cephalus latus, nearly ripe ; and C, Dipylidium caninum, ripe. 



C.S., cirrus sac ; G., genital aperture ; U., uterus full of eggs ; V., vagina ; Vi., vitellarium. 



separate pore on the opposite lateral margins, 

 host is a parasitic louse or flea. 



Its intermediate 



Two problems call for attention in the tapeworm, its 

 segmentation and the question of the alternation of generations. 



It is obvious that there is a considerable difference between the 

 proglottids and the somites of such a form as Lumbricus. In the 

 first place new segments in the Earthworm are produced throughout 

 the period of growth, immediately in front of the last or anal somite, 



