PLATVAELVMINTHES 
103 
Further, the separation of parts of the body containing repro- 
ductive cells occurs in the hectocotylsation of the Cephalo- 
pods, and this is no longer regarded as an instance of 
alternation of generations. 
It is an interesting fact that, with the exception of Archigetes, 
which inhabits the Oligochaet Tubifex rivulorum, the sexual form 
of the Cestoda are entirely confined to Vertebrate hosts. 
The 
Cysticercus form, although usually found in Vertebrata, has also 
been observed in the bodies of Molluses, Arthropods, and Worms. 
Some interesting divergences from the arrangements of the 
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Fra. 70.—Bothriocephalidae. 
A. A segment of Bothriocephalus latus, 
showing the generative organs from 
the ventral surface. 
Excretory vessels. 
Cirrus. 
Cirrus pouch. 
Vas deferens. 
Vaginal opening. 
Vagina. 
Shell gland. 
Oviduct. 
Ovary. 
COICO CTU ACO; ROE 
10. Yolk glands. 
11. Their duct. 
12. Uterus. 
13. Uterine opening. The testes are not 
visible from this side. x 23. 
From Sommer and Landois. 
B and C. Marginal and lateral view of B. 
cordatus, showing the cephalic 
grooves. x 5. From Leuckart. 
D. Ciliated larva of B. latus. x 60. 
From Leuckart. 
organs in Taenia are met with in Bothriocephalus latus, the 
largest Cestode which inhabits the human intestine; it may 
