EMBEYONIO FISSION IN OYOLOSTOMATOUS POLYZOA. 233 



egg is completely enclosed is shown in Braem's pi. xv, fig. 171, 

 while in fig. 172 the '^ooecium" has difi'erentiated oflp a distal 

 portion which may be the exact equivalent of the " tentacle- 

 sheath '' shown in ray own fig. 3 for Crisia. The tendency 

 to precocious fission shows itself in Phylactoljemataj how- 

 ever, in the precocious formation of a considerable number 

 of polypides, particularly in Cristatella; — a process which 

 is of course very diff'erent from the embryonic fission of 

 Crisia. 



The ovicells of the Cheilostomata are probably not homo- 

 logous with those of Cyclostomata. They are probably not to 

 be regarded as modified zooecia, since the ovicell is an appen- 

 dage of a fertile zocecium, and ordinarily contains a single 

 embryo. 



Similarly in the other groups which have been mentioned 

 precocious fission is not characteristic of the whole group, but 

 occurs sporadically; — in Coelenterata, in Oceania, Cunina, 

 &c. ; in Trematoda, in the Distomeae ; and in Tunicata in the 

 Thaliacea, and in some Synascidians. 



Although I must regard the question as a very open one, 

 the conclusion which appears to me to be suggested by the above 

 facts is that one is not justified in assuming that the budding 

 of the Polyzoa, for instance, commenced with the acquirement 

 of a habit of embryonic fission like that found in Crisia, but 

 that the embryonic fission may be the consequence of the pre- 

 viously acquired power of adult budding. It may be pointed 

 out that the embryonic fission of Crisia gives rise to numerous 

 larvse, each of which may form the starting-point of a new 

 colony. In the case of adult Polyzoa, the result of budding- 

 is merely to increase the number of individuals in a colony, 

 with the exception of Loxosoma (in which the bud normally 

 becomes free) and of certain dendritic forms of colony, in 

 which the decay of the proximal part of the colony leads to 

 the separation as distinct colonies of what were at first merely 

 branches, or of cases like that of Crisia itself, where new 

 colonies are formed by the upgrowth of new stems from a 

 creeping rootlet, which acts as a stolon for the production of 



