voi.. 3] Robertson. — Embryonic Fission in Crista. 123 



of the branches. Such a pr i<ms appearance of ova is reported 



in a few instances among the Cheilostomata (Calvet '00), but as 

 far as I am aware no other case is known in which the ovary its< If 

 is thus precociously formed. The early appearance of the germ 

 cells in Grisia is somewhat comparable to what takes place in the 

 Hydromedusae ('90) . In both classes of animals it is a secondary 

 condition correlated with the subordination of the sexual indi- 

 viduals, and the assumption by the colony of the reproductive 

 function. 



Throughout the bryozoa the sexual elements are produced, as 

 a rule, in the zooeeia and in connection with the polypides. 

 Thus, Xitsche ('69) found that in Bugula the ova arise from the 

 inner surface of the endocyst of the younger zooecia. In the 

 older zooecia he found the spermatozoa and in still older ones, 

 the fertilized ova. Yigelius ('84) reports that in Flustra mem- 

 branacea-truncata the genital products, both male and female, 

 also arise from the endocyst of the zoceeiunj, aud Prouho ('92) 

 in a series of observations upon the Ctenostomes, found essen- 

 tially the same condition as far as the time and place of origin of 

 the sexual elements are concerned. 



More recently, Calvet ('00) has reported a series of observa- 

 tions upon no less than forty-four species of marine bryozoa. 

 These studies have reference mainly to the Cheilostomata and 

 the Ctenostomata, his study of the Cyclostomata having been very 

 restricted. In one species of the Cyclostomata. viz.. Grisiadenti- 

 culata, he made some observations mi the reproductive processes, 

 corroborating the researches of Harmer on the fission of the 

 embryo. In the list of species whose spermatogenesis he studied, 

 he mentions two Cyclostomes: C. denticulata and Tubulipora 

 flabellaris. In his discussion he makes no particular mention of 

 them, however, merely including them in the list with others, in 

 which he says the primitive sperm cells originate as in Bugula 

 sabatieri, i.e., in the vicinity of the funicular cord in the lower 

 portion of the zocecium. One can only infer that he made no 

 investigation of the growing tips of these two species, and the 

 slimy of the adult animals alone would certainly mislead one as 

 to the time and place of origin of the spermatoblasts. 



Calvet's study of ovogenesis in Bugula sabatieri reveals an 



