ON THE DEVELOPMENT OF TUBULIPORA. 125 



phenomenon has been described in Cheilostomes (Bugula) by 

 Claparede (4^ p. 166). 



The eggs appear as part of the outer or mesodermic layer of 

 the polypide-bud. In some colonies they are very numerous. 

 Thus in one case (T. plumosa) a young bilobed colony con- 

 tained twenty-three individuals in which an egg or eggs had 

 become unmistakable. Some of these were fully formed 

 polypides, others very young buds, the youngest belonging to 

 a stage when the bud consisted of a two-layered cell-plate 

 which had not yet become vesicular. All stages intermediate 

 between these extremes were represented. 



In most of the zooecia there is only a single egg; in six cases 

 there are two, and in one case three eggs ; the position being 

 at or near the proximal end of the polypide-bud or the csecum 

 of the polypide, as the case may be. Each egg (whatever the 

 number in a zooecium) is surrounded by a very distinct follicle 

 (fig. 10) of cells, in which a follicle-cavity is usually visible. 



There can be no doubt of the normal occurrence of eggs in 

 the manner above described, since they are repeatedly noticed 

 in the sections. I think, moreover, that there is clear evidence 

 that the eggs occur especially in young lobes. When a lobe 

 possesses an ovicell belonging to one of the later stages, 

 although eggs may not be altogether wanting, they cease to 

 be the conspicuous feature that they form in young lobes 

 during the breeding period. It is thus probable that the suc- 

 cessful development of an egg, with the resulting modification 

 of the fertile zooecium into an ovicell, diverts the energies of 

 the lobe from the production of fresh eggs to the nutrition of 

 the embryos, although new lobes may be formed from the 

 same colony and give rise to new ovicells. 



The mature egg reaches a diameter of 24 fx or even 28 /j. 

 (T. plumosa), and this measurement is larger than those pre- 

 viously recorded for Crisia (17*6 fx) and Lichenopora 

 (16 ju). It possesses a distinct germinal vesicle and germinal 

 spot, and it commonly has a paranuclear body lying in its 

 protoplasm. This body might possibly be a male pronucleus, 

 against which is to be set the fact that the nucleus of the egg 



