POLYZOA 187 
Most species of the Entoprocta are dioecious, and the 
generative organs have special ducts. Besides the sexual 
reproduction, they multiply also by the formation of buds. 
This process amongst the Polyzoa is remarkable, inasmuch 
as the endoderm is not represented in the tissues of the bud ; 
in most other animals which reproduce by budding, all the 
three embryonic layers occur in the bud. 
The affinities of the Polyzoa are somewhat obscure. The 
developement of the Entoprocta and their adult structures 
point to the origin of the group from some ancestor which 
is represented in the ontogeny of the Mollusca, Chaetopoda, 
and armed Gephyrea by the Trochosphere larva. On the 
other hand, the Phylactolaemata have a certain marked resem- 
blance to the unarmed Gephyrea, and if this resemblance 
be not homoplastic, we must regard the Gymnolaemata, and 
still more the Entoprocta, as degenerate forms. 
