34 SIDNEY P. HARMER. 



parous method of reproduction in the adults of the above- 

 mentioned groups been preceded by larval fission, possibly 

 induced by the separation from the embryo of individualised 

 blastomeres or groups of blastomeres, or is the embryonic 

 fission the result of the precocious acquirement of the budding 

 habit which characterises the adult ? Now in the Polyzoa, 

 embryonic fission is by no means a common phenomenon, 

 although the adults of all known Polyzoa possess the power of 

 budding ; and although it is probable that the method of re- 

 production above described in Crisia will be found to be 

 characteristic of all Cyclostomes. I have no sufficient evidence 

 on this point at present, but it may be pointed out that the 

 ovicells of Cyclostomatous Polyzoa invariably (so far as I know) 

 contain a large number of embryos. My own observations 

 enable me to state further that the general structure of the 

 ovicell in Idmonea serpens and in Diastopora patina 

 agrees with that in Crisia; and T have little doubt that I 

 shall be able to show that embryonic fission is characteristic of 

 Cyclostomes in general. The development of thePhylactolsemata 

 possibly oflfers some analogies to this process. The structure of 

 the larva is somewhat similar to that of Cyclostomes, and 

 the early development, according to the account given by 

 JuUien (19), is not unlike that of Crisia. Braera (5) has also 

 given an incomplete account of the development of PI u ma- 

 tell a, which suggests further resemblances to the Cyclosto- 

 mata. The two layers which form the wall of the embryo, and 

 which are considered by Braem to represent ectoderm and 

 body-cavity epithelium respectively,^ are obviously comparable 

 with the two layers shown in PI. Ill, figs. 22 and 23, of 

 Crisia. The manner in which (in Plumatella) a rudi- 

 mentary bud encloses the egg, forming the "ocecium," is again 

 strikingly suggestive of Crisia. ^ The first stage in which the 



' Tbe same conclusion is arrived at by Davenport (8a), whose valuable 

 paper should be consulted for a comparison of the larva of Phjlactolaemata 

 with that of Gjmnolaemata. 



* Compare in particular the woodcut given by Braem in his explanation to 

 fig. 171. 



