Miscellaneous. 387 
minal vesicle, besides the nucleolus, a cellular element rather smaller 
than the nucleolus, and situated at a variable distance from the 
latter. This excentric element is itself provided with a small, very 
distinct nucleus. At first widely separated from the nucleolus, it 
approaches this by degrees, and finally becomes applied to its surface, 
when it flattens out and assumes the form of a double hood (calotte). 
Becoming more and more closely applied to the nucleolus, it loses its 
nucleus, and in the end becomes reduced to a double membrane 
which surrounds the nucleolus as the pericardiac serous membrane 
surrounds the heart. Finally its substance unites with that of the 
nucleolus; and the mature ovum then presents no trace of this sin- 
gular phenomenon. 
I repeated this observation many times at the end of last Septem- 
ber. The whole process is perfectly visible in the fresh ovum taken 
from the interior of the maternal organism, and without the employ- 
ment of any reagent. Verick’s objective is quite sufficient for 
following the phenomenon. The employment of picrocarmine, by 
distinctly limiting the germinal vesicle, shows clearly that it is not 
the nucleus of the ovum, but its nucleolus (Wagner's spot) that 
conjugates with the excentric cellular element. 
I do not know how this element penetrates into the germinal 
vesicle, or what is its origin. J have met with it once or twice out- 
side the germinal vesicle in the vitellus, where it is more difficult to 
distinguish it and to follow its progress, in consequence of the greyish 
granules of the vitelline mass. 
The significance of this phenomenon of prefecundation I am still 
unable to “Tundlanstecndl I have nevertheless thought that I ought to 
make known these facts, on account of their importance and the 
facility with which they can be checked. 
I think that there are great differences between this observation 
and the more or less analogous observations formerly published by 
M. Balbiani. Perhaps there would be no difficulty in observing the 
same process in the ovarian ovum of Sternaspis scutata. It is in this 
way, at least, that 1 think we may interpret the appearances figured 
by M. Franz Vejdovsky, in an excellent memoir quite recently pub- 
lished*. The element designated the “‘ Buckelchen ” by the Prague 
professor seems to be nothing but the migratory cell in conjugation 
with the nucleolus.—Comptes Rendus, Oct. 17, 1881, p. 600. 
Some new Genera of Freshwater Sponges. . 
Mr. E. Potts referred to a recent paper by H. J. Carter, F.R.S. 
(Ann. & Mag. Nat. Hist., Feb. 1881), entitled “The History and 
Classification of the Known Species of Spongilla,’ in which the 
writer has distributed the species, heretofore grouped under one 
generic title, among five genera, founded upon the differences in 
form and arrangement of the spicula surrounding the statospheres. 
* F. Vejdovsky, ‘Untersuchungen uber Anatomie, Jelinyauoliogue und 
Entwicklung von Sternaspis’ (Vienna, 1881), pl. viii. figs. 2,11, 12, and 13. 
