Royal Physical Society. 229 



The polypary lies between the ridges, and consists of fleshy 

 fibres, from which the polyps spring. I believe a thin ring or 

 cup incloses the base of each polyp, and that a membrane also 

 passes from the summit of each ridge to that of the one next 

 it; but I have not been able to satisfy myself on these points. In 

 other parts of the same polypidom the ridges assume the aspect 

 of an intricate net-work, or even a spongy mass, in which the 

 chitinous and fleshy elements are intimately blended together. 

 The whole mass of the polypary, corallum, and polyps, is rea- 

 dily detached from the fucus. [Since writing the above descrip- 

 tion, I have convinced myself, by the examination of Mr Good- 

 sir's specimen, that the corallum of Clava cornea is formed of 

 tubes cemented together, either laterally in sub-parallel lines, 

 or in a more complicated mass. The surface of the corallum 

 of this zoophyte, in fact, has a strong resemblance to the stem 

 of the corallum of Halecium halecinum, which consists of a 

 bundle of sub-parallel and anastomosing tubes, more or less 

 closely cemented together, a structure which becomes beauti- 

 fully apparent in transverse section.] 



6. Reproduction of Clava. — All the three species of this 

 zoophyte which have come under my observation are unisexual 

 or dioecious ; that is to say, the polyps connected by the same 

 polypary have either spermsacs or ovisacs, but not both. The 

 reproductive capsules are amassed together, like bunches of 

 grapes, in one or more thick pedicles, which arise from beneath 

 the lower range of tentacles of the polyp. 



In my communication on Hydractinia,* I stated (after All- 

 man and Huxley) that the polyps of all the hydroid zoophytes 

 consisted of three elements: — 1st, The ectoderm or outer layer, 

 the seat of sensation and other external relation, furnished 

 with tactile processes, and with apparatus of offence or defence. 

 2d, The muscular or middle coat, specialized for motor func- 

 tion ; and, Sdly, The endoderm or inner coat, of which last, 

 again, the inner surface is endowed with the nutritive function, 

 while its outer surface subserves to that of reproduction. It 

 is necessary to remember the relation and function of these 

 layers when describing the reproductive apparatus of Clava. 



* Vide ante, p. 192. 



