506 POLYZOA 



Reproductive Processes of Polyzoa in general. 



In studying the reproductive processes of Polyzoa, we have 

 to deal with two very distinct phenomena ; firstly, with the 

 development of eggs ; and secondly, with the formation of buds. 



The process of budding usually does no more than increase 

 the number of individuals in a colony which already exists, and 

 is seldom responsible for the commencement of a new colony. 

 In Loxosoma, however, the buds break off and lead an independent 

 existence ; and in the Phylactolaemata a large proportion of the 

 colonies have their origin in the statoblasts. In certain cases, 

 again, new colonies may be formed by the detachment of parts of 

 an old one, as by the fission of Cristatella and Lophopus, or by 

 the breaking up of a richly-branched species into several colonies 

 by the decay of the proximal parts. 



We may then in the majority of cases look to an embryo for 

 the foundation of a new colony. The embryo develops into a larva, 

 which, after a period in which it swims freely, settles down, and 

 is metamorphosed into the first zooecium. This primary individual 

 forms the starting-point of a colony, and often differs to a con- 

 siderable extent from the other zooecia which arise from it. 

 In Cyclostomata, for instance, the proximal end of the primary 

 zooecium permanently retains the disc-like shape assumed by 

 the young larva when it first fixed itself. The primary zooecium 

 may be recognised with equal ease in many Oheilostomata, and 

 may differ from its successors by possessing a richer development 

 of marginal spines, or in other respects. 



Reproductive Organs. -Eggs and spermatozoa are commonly 

 found in the same colony, either in different individuals, or else 

 in the same zooecium (see Fig. 234, p. 469). In some cases, 

 the zooecium first develops spermatozoa, and later eggs. The 

 Entoprocta have a more marked separation of the sexes than 

 obtains in other Polyzoa. The genus Loxosoma. is perhaps always 

 dioecious (i.e. with separate sexes). PediceUina is sometimes found 

 with ovaries and testes in the same individual, sometimes with 

 these organs in different individuals ; and it is not clear whether 

 a given species always behaves alike in these respects. 



The reproductive organs of the Entoprocta open by ducts of 

 their own into the vestibule. In the Ectoprocta they are 

 developed in the body-cavity, and they have no ducts. 



