vol.3.1 Robertson. — Embryonic Fission in Crisia. 125 



buds of every stage of growth. In Lichenopora ('97), he found 

 but one egg, as a rule, in each colony, and always in the second 

 or third zocecium, and when the polypide was very young. In 

 all these cases he regards the egg as "probably differentiated in 

 situ from the outer layer of a young polypide hud." or, "The 

 eggs appear as part of the polypide hud." Or again, "The eggs 

 (of Tubulipora) are developed at a very early stage by the polypide 

 buds, as in Lichenopora and Crisia." Furthermore, he found an 

 egg-like cell 9.6^ in diameter at the growing margin of a colony 

 of Lichenopora. He did not feel sure that this was normal, 

 although as he says, it recalls the condition in Crisia. In his 

 study of embryonic fission this observer made no special study 

 of the origin of the sexual elements. He explains the occurrence 

 of ova at the growing margin as due either to the productive- 

 ness of the young buds, or as an unusual, perhaps abnormal 

 phenomenon. 



In Crisia one fails even in the height of the breeding season to 

 find even a rudimentary ovary within the individual zocecia, or else- 

 where. What becomes of the relatively large number of ova? Do 

 they all reach maturity? If not. what is their fate? In answer 

 to these questions it is to be said that all ova do not produce 

 embryos. According to their fate they fall into three classes. 

 The first (a), comprises the relatively small number that produce 

 embryos within an ovicell. The second (6), includes the small 

 number which reach a partial development within the zocecia, and 

 the third (c) , includes the remainder which fail of development 

 entirely. 



It has already been shown in the ease of the male colony that 

 proximal to the region where the germ cells are formed is the 

 budding region, and further that in order that the male germinal 

 cells may complete their development, they must become united 

 with a polypide bud. (PI. XII, Fig. 4, /»/. bd. J.) In a similar 

 manner, in order that an ovum may reach maturity, it is neces- 

 sary that a union should be effected with a polypide bud. In 

 his account of the reproductive pi-ocesses in the Cyclostomata, 

 Hariner ('!):;) has shown that a peculiar relation must exist 

 between a bud and an ovum, in order that an ovicell should be 

 formed. He says: "One of these (egg-cells) acquires a close 



