PLA TYHELMINTHES 



103 



Further, the separation of parts of the body containing repro- 

 ductive cells occurs in the hec.tocotylisation 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 oi 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 Molluscs, Arthropods, and Worms. 



Some interesting divergences from the arrangements of the 



FiQ. 70. — Bothriocephalidae. 



A. 



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 Leuokart. 

 D. Ciliated larva of B. latus. x 60. 

 From Leuckart. 



organs in Taenia are met with in BothriocepJialus latus, the 

 largest Cestode which inhabits the human intestine ; it may 



