146 SIDNEY F. HARMER. 



drical zooecium, but begins to widen from its commencement 

 (cf. 13, pi. xii, fig. 6). The ovicell develops a polypide-bud, 

 which does not become a polypide, but gives rise to the tissues 

 immediately surrounding the primary embryo. There is thus 

 no fertile brown body. In Tubulipora the ovicell is at first 

 a zooecium with a functional polypide. Degeneration of the 

 latter takes place at the beginning of the development of the 

 embryo, and at a time when the polypide is still moderately 

 young; and a brown body results. In Lichenopora (16) 

 also the young ovicell is a zooecium, but it has two successive 

 polypides, the second of which is present until the primary 

 embryo has developed for some time, and the embryophore has 

 been formed. 



The investigation of Crisia appeared to show that the 

 rudimentary polypide-bud of the ovicell gave rise to a tentacle- 

 sheath, which communicated with the exterior by means of a 

 vestibule (described as '' aperture " in 16). The cavity of the 

 embryophore in Tubulipora is so similar to the "tentacle- 

 sheath " of the ovicell of Crisia that at first I had no doubt 

 that the two spaces were homologous. The cavity in Tubu- 

 lipora is, however, a completely new formation, formed after 

 degeneration of the fertile polypide. If then it is a tentacle- 

 sheath at all, it must be that of a newly formed bud. 



In my paper on Lichenopora (16, p. 114) I have alluded 

 to this possibility for that genus. The evidence aiForded by 

 Tubulipora seems to be in favour of the hypothesis that the 

 parts of the embryophore correspond with parts of a polypide- 

 bud. This view is supported, for instance, by the great 

 resemblance of the vestibule of the ovicell to that of the 

 zooecia, in its structure and in its relation to the terminal 

 membrane. The polypide-bud would be represented by the 

 cellular investment which appears round the brown body. 

 This mode of origin is probably similar to those cases Avhich 

 have been recorded by Smitt and Hincks (18, p. Ivii) among 

 Cheilostomes, iu which the young polypide-bud appears to 

 grow out of the brown body. 



The relations of the cavity of the embryophore to the vesti- 



