ON THE DEVELOPMENT OP TUBULIPORA. 81 



roof on the terminal membrane, which is, so to speak, gra- 

 dually constricted until it completely disappears. 



My study of Tubulipora has fully confirmed the conclusion 

 stated in my paper on Crisia (13, p. 128), that the form of the 

 orifice of the ovicell is of great importance for the discrimination 

 of the species. As I am convinced that this structure will become 

 increasingly important in the systematic study of the Cyclo- 

 stomata, I venture to think that a special terminology may be 

 convenient for descriptive purposes; and I therefore propose 

 to term the passage by which the larvae escape from the 

 ovicell the " ooeciostome," and its actual external orifice the 

 " ooeciopore." The ooeciostome is usually a tubular or funnel- 

 shaped structure, as in the species of Tubulipora here de- 

 scribed, and in many other Cyclostomes. The part connecting 

 the cavity of the ovicell with the ooeciopore may be termed 

 the "tube^' of the ooeciostome, whatever its shape. The tube 

 is not a necessary part of the ooeciostome, since it is absent in 

 Crisia aculeata, Hassall, in which the ooeciopore represents 

 the entire ooeciostome. 



The structure of the wall of the tube is commonly different 

 at its two ends. The proximal portion is often pierced by 

 pores identical with those in the roof of the ovicell, of which 

 it is a direct continuation (fig. 1), while the distal portion 

 is imperforate. Valuable specific characters are afforded by 

 the shape, size, and relations of the ooeciostome^ and by the 

 size and position of its tube and ooeciopore. 



The constancy of the characters of the ooeciostome has been 

 verified by the examination of numerous specimens of several 

 species from various localities. While the shape and size of 

 the entire colony, and therefore of the ovicells, has been shown 

 to be highly variable, the ooeciostome retains its character, 

 whatever the condition of the colony. I do not, of course, 

 mean to assert that there is no variation in the ooeciostome. 

 Variation does occur, sometimes within fairly wide limits; but 

 it is usually possible to decide the species at once by an 

 inspection of its ooeciostome. In order to do this it may be 

 necessary to have a fully developed ooeciostome, since the 



VOL. 41, PART 1. — NEW SKR. F 



