ON THE DEVELOPMENT OP TUBULIPOEA. 129 



Tubulipora, and this is probably because the stage is of 

 short duration. Two possibilities have to be considered, — (a) 

 that degeneration takes place while the polypide is still a 

 bud ; {b) that it occurs after the polypide has become functional. 

 The latter view is probably the correct one, and if this is so, 

 Tubulipora occupies an intermediate position in this respect 

 between Crisia, in which the polypide degenerates while it is 

 still a two-layered bud, and Lichenopora, in which two 

 functional polypides successively occupy the young ovicell. 



The question clearly turns on the observation of the stage 

 at which the egg begins to develop. No trace of development 

 is found in the eggs of polypide-buds, and on the assumption 

 that the brown body is formed by the degeneration of a bud, 

 it would be necessary to assume that the large eggs which are 

 so commonly noticed in the ovaries of polypides have missed 

 their chance of developing, and would later have degenerated. 

 Positive evidence that the fertile brown body is formed from a 

 polypide, and not from a mere bud, is afforded by the fact that 

 the youngest embryophores found with a brown body and 

 partially developed embryo occur in fully formed, long zooecia, 

 and not merely in immature zooecia still in process of develop- 

 ment at the growing edge. 



Even more direct evidence is, however, aff'orded by the stage 

 shown in fig. 11 (T. plumosa), which represents what is 

 certainly a case of the division of the egg. The darkly stained 

 bodies marked / probably represent degenerating eggs or 

 their follicles. This would indicate that in the event of more 

 than one egg occurring in a single ovary, only one of the eggs 

 actually develops. The figure shows the caecum of the fertile 

 polypide, which from its size, and from the avidity with which 

 its tissues have taken up haematoxylin, was clearly only just 

 mature. Its rectum contains Diatoms, a fact which proves 

 that the polypide had commenced to feed. A second, pre- 

 cisely similar polypide, containing Diatoms, and provided with 

 an egg in the same condition as that of the first specimen, also 

 occurred in the same colony. Most of the buds and young 

 polypides in this colony, if not all of them, possessed either 



VOL. 41, ?ART 1. NEW SERIES. I 



