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 Httle 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 
mesembryantheinum. 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. 
