428 
MR. T. H. HUXLEY ON THE AFFINITIES OF THE MEDUSAE. 
foundation membranes, the generative elements being developed between them, 
figs. \ a, \ \ a, 18 a, 26 a. 
67. In the Diphydse (and as 1 have good reason for believing in the Physopho- 
ridae also) the generative organ commences as a simple process of the common tube 
(fig. 39 a), and undergoing great changes of form in the course of its development 
{b, c), it becomes at last exactly similar to an ordinary natatorial organ with a 
sac composed of twm membranes suspended from its centre, fig. 39. In external 
form it greatly resembles such a Medusa as Cytceis, and this resemblance is much 
heightened when, as in some cases, it becomes detached and swims freely about, 
fig. 41. The ova or spermatozoa, as the case may be, are developed between the two 
membranes of the sac, the inner of which at any rate is a continuation of the inner 
membrane of the common tube, fig. 39. 
68. The ovarium of the Plumularia above mentioned (65.), commences as a 
dilatation of the apex of its pedicel, which again is a process of the common stem. 
It then becomes lenticular with a horny outer wall, glassy and transparent externally, 
but internally coloured by pigment masses. Internally it has an oval cavity com- 
municating with that of the stem and lined by a distinct membrane, fig. 45. Be- 
tween the two membranes is a thick layer of ova, more or less oval in shape, and 
about ^3^th of an inch in diameter, with a germinal spot about -^woth of an inch in 
diameter, seated in the middle of a clear space about twice that size, which doubtless 
represents the germinal vesicle. 
69. The account given by Lowen of the generative organs of Campanularia 
differs considerably from the foregoing. After all however his ‘^female polypes” 
may be nothing more than ovaria similar to those of Diphyes or Coryne, but having 
the production of tentacles from the margin carried to a greater extent than in the 
latter. If this be a correct explanation, the idea promulgated by Steenstrup, that 
there is an “ alternation of generations” among the Sertularian Polypes, must be 
given up. 
70. In Hydra*, the ova are developed in similar processes of the lower part of 
the body. But among the Hydroid Polypes the ovaries of Coryne, Syncorine and 
Corymorpha, as described by Sars, Lowen and Steenstrup, are most interesting. 
They commence as tubercles of the stem, afterwards become bodies, precisely re- 
sembling the ovaria of the Diphydee, and finally (fig. 42) detaching themselves deve- 
lope regular tentacles from their margin. The ova are formed between the tw’o 
membranes of the inner sac'f'. 
* M. Dujardin, Annales des Sciences Naturelles, November 1845, states on the authority of Ehrenberg, 
CoRDA and Laurent, that the ova of the freshwater Polype are “produits dans I’epaisseur meme du tissu sans 
ovarie ni ovule prealable.” 
t “ The axis of the bell is occupied by a membranous sac, which is a prolongation of the nutritive canal, and 
answers to the alimentary cavity of the alimentary Polypes. The ova are developed in regular series in the 
interval between this alimentary capsule and the parietes of the outer sac, in an intermediate membranous sac, 
distinguished by its yellowish brown colour.” — Cuvier, Le 9 ons d’Anat. Comparde, t, viii. Organs de Gene- 
ration des Zoophytes, p. 860. See also Duvernoy, Annales des Sciences Naturelles for November 1845. 
