220 Proceedings of the Royal Physical Society. 



low, cnidophorous or sting-cell-bearing tentacles found on 

 the inner surface of the ovarian membrane of Medusa aurita 

 and Lucernaria auricula; they are simply, as are the grape- 

 like bodies, prolongations of the endoderm and gelatinous 

 layer of the ovarian membrane. 



Although the testicles of Chrysaora are apparently not 

 homologous with those of other zoophytes, yet in reality 

 they differ but little from those of Actinia and Lucernaria. 

 I have given, in Plate IX. fig. 2, a section of the testicle of 

 Chrysaora, and in fig. 3, of one of the same bodies in Actinia 

 mesembryanthemum. In Chrysaora, the thin endoderm (a) 

 forms the distant sperm-sacs which project from the surface. 

 In Actinia, the thick endoderm (a) also forms the more 

 closely aggregated sperm- sacs, and fills up the interstices 

 between them. The testicle of Lucernaria, again, resembles 

 in shape and structure fig. 3; but the sperm-sacs are so 

 closely moulded together, that they form hexagonal prisms 

 divided from each other by exceedingly delicate walls of 

 endoderm. 



The sperm-sac of Chrysaora (fig. 4),. as well as of other 

 Steganophthalmatous Medusae, Lucernarias, and Actinias, is 

 thus always formed of the endoderm or lining membrane of 

 the digestive system, while the sperm -sac of Hydra (fig. 5), 

 the Hydroid Polyps, and the Gymnopthalmatous Medusae is 

 formed of the ectoderm. In the first class of animals the 

 spermatic cells (fig. 4) become first matured into sperma- 

 tozoa in the centre (c), or at the base of the sperm-sac, the 

 part most distant from the endoderm (a). In the second 

 class they ripen at the periphery, or at the summit of the 

 sperm-sac (fig. 5), the part also most distant from the en- 

 doderm (a). 



My friend Mr Hincks, in his valuable paper on " Clava- 

 tella "* appears to consider that the ova of that creature may 

 be developed from the ectoderm. But an examination of the 

 embryology of a very large number of zoophytes forbids me 

 to entertain this idea. The endoderm of the generative cap- 

 sule in these creatures consists of two layers intimately con- 

 nected with each other. The external layer, or that in 



* Annals and Magazine of Natural History for February 1861. 



