124 SIDNEY P. HARMER. 



The account of the development will, as far as possible, be 

 described as a series of stages corresponding with those which 

 I have formerly described in Lichenopora (16, p. 99). 

 Those stages were characterised partly by the degree of 

 development of the embryo and embryophore,^ and partly by 

 the condition of the fertile polypide. This latter degenerates 

 at an earlier stage in Tubulipora than in Lichenopora, 

 and the correspondence between the developments is therefore 

 not exact. 



The stages selected for descriptive purposes are thus as 

 follows : 



Stage A. Formation of the definitive egg (fig. 10). 



Stage B. Division of the egg, and degeneration of the fertile 

 polypide (figs. 11 — 13). 



Stage C. [Not represented in Tubulipora.] 



Stage D. Formation of the embryophore. The fertile 

 zocEcium is still cylindrical, or slightly expanded distally, and 

 its brown body becomes closely surrounded by a distinct cel- 

 lular investment (figs. 14 — 18, 21). 



Stage E. The investment of the brown body becomes vacuo- 

 lated, so as to give rise to a cavity. The ovicell expands dis- 

 tally (figs. 19,20, 22,25,32). 



Stage F. Commencement of embryonic fission. 



Stage G. Fully formed ovicell (figs. 1—8, 33). 



Stage A. — Formation of the Definitive Egg. 



The eggs are developed at a very early stage by the polypide- 

 buds, as in Lichenopora and Crisia. This precocious 

 occurrence of the eggs appears to be in some way correlated 

 with a colonial habit, and cases of this kind are familiar to 

 every student of colonial Ascidians and of Hydroids. The 



1 The term " embryophore " will be used below to denote the structures, in 

 relation with the primary embryo and its derivative secondary embryos, which 

 are on the proximal side of the vestibule. The principal contents of the 

 ovicell are thus the embryophore, containing the embryo and the fertile brown 

 body, the vestibule, and the terminal membrane. 



