418 REPORT— 1863. 
non-sexual term intermediate between the ovum and the sexual medusal 
term. 
Against the absolute universality of this law, however, certain observa- 
tions have been adduced as tending to show that, in some cases, a direct 
development from the egg to the medusa takes place without the interven- 
tion of a non-sexual trophosome. Nevertheless a careful examination of 
those cases will render it evident that, with one sole exception, they afford 
no proof of the direct development of the medusa from the egg. As, how- 
ever, the observations referred to present examples of a true metamorphosis, 
and are in other respects by no means without interest in the present 
inquiry, I shall here give an analysis of them, with the view of rendering 
apparent their real bearing and significance. 
IT shall first notice a set of observations which have been made upon 
certain medusz belonging to the family of the yinide—a group, however, 
with regard to whose exact systematic position there is some uncertainty, 
since in many of their characters they approach nearest to the true hydroid 
medusa, while in others they look towards the Discophora. 
Whatever view we may be disposed to take of their nearest affinities, the 
Ayinide possess so many points in common with the Hyprorpa, that the 
developmental phenomena observed among them can scarcely be overlooked 
in the present inquiry. 
The first important observation bearing directly on this question is due to 
Joh. Miiller*, who frequently captured, in the sea at Marseilles and Nice, a 
minute free-swimming hydroid. It was of an oval form, about half a line in 
its longer diameter, ciliated over its entire surface, with two tentacula-like 
processes near one end, and having at the opposite end an opening which led 
into a central cavity. 
Miiller considers this little animal to haye been developed directly from 
the egg, and from its resemblance to a peculiar two-tentacled medusa 
which he obtained in considerable abundance at Nice, he believes himself 
justified in regarding it as one of the stages in the development of this 
medusa, into which he supposes it to pass by direct metamorphosis. He 
refers it to the genus Ayinopsis, Brandt, and names it A%ginopsis Mediterranea, 
Miill. Miiller does not seem to have obtained any specimens of his 4. Medi- 
terranea so far advanced as to present traces of the generative elements ; but 
his observations have been in this respect supplemented by Kollkert, 
who afterwards obtained the same species at Messina in a sexually mature 
state. 
Now we cannot overlook the fact that Miiller has not, in the above case, 
traced his ciliated hydroid through a continuous series of developmental phases 
into the adult form of Ayinopsis ; and, without denying the probability that 
the ciliated bitentacular hydroid is really the larva of the AZgiopsis, we 
cannot regard this relation as absolutely proved, while there is no evidence 
whatever that the ciliated form is the immediate result of the development 
of an ovum. Indeed, its remarkable ‘resemblance to the singular generative 
zooid of Dicoryne (see above, p. 365) would seem to show the probability of 
another origin than that by direct development from the egg. Muller, led 
apparently by the analogy of the planula-stage of the Hydroida, considers 
the ciliated condition of the surface as affording evidence of such a direct 
development; but the fact that the Dicoryne-zooid is also richly ciliated 
over its ‘whole surface shows that this argument goes for nothing. 
* Miiller’s Archiv, 1851, p. 272. 
+ Zeit. f. wissen. Zool. vol. iv. p. 327. 
