Miscellaneous. 449 
must disappear, and that, asin all the Rotatoria, the central nervous 
system occurs in these animals on the anal or dorsul side, and con- 
sequently in the curvature of the digestive tube. 
Reproduction.—During the whole summer we find three kinds of 
_ ova in the tubes inhabited by the Melicerte, namely :—male summer- 
eggs, Which are the smallest, and haye not previously been indicated ; 
female summer-eggs, of larger size; and, lastly, winter-eggs, which 
are still larger, and exceedingly opaque at the moment of deposition, 
and which afterwards become encysted in an ornamented chitinous 
membrane within the first chorion. These different ova are not 
produced by all the females indiscriminately, but each one has, so 
to speak, its specialty. 
Formation of the Ovum.—It is to be remarked that in the ovary 
of the Rotatoria all the ova are of uniform aspect, and appear to be 
equally advanced, with the exception of a single one, which, being 
detached from the ovary and placed in that portion of the envelop- 
ing membrane that may be called the sac of maturation, is always 
strongly granular, and increases in size with such rapidity, that in 
less than twenty-four hours it attains a volume more than fifty 
times that which it had retained for some weeks in the ovary. ‘This 
result and these appearances are explained by the fact that the 
stroma of the genital gland constantly secretes a great quantity of 
granules of deutoplasm. ‘These granules the freed ovum aggluti- 
nates rapidly, and mixes with its own vitelline substance. In 
certain Hloscularic, in which the sae of maturation does not exist, 
and in which the ovum, when detached from the ovary, falls into 
the general cavity, we see these granules circulate and spread every- 
where in the body, even into the limb and the peduncle, and then 
unite with the ovum, which increases in size rapidly. I cannot 
help seeing in these facts a sort of sketch of what takes place in 
many Turbellaria and in the Trematoda, in which a supplementary 
vitellus furnished by special glands (vitellogene) is added to the 
ovum (germinal vesicle of Van Beneden) as it issues from the ovary 
(germigene). 
Winter-Egg.—There has been much discussion as to the nature 
of the winter-egg. Huxley regards it, not as a true ovum, but as 
a portion of the ovary separated from the rest, a sort of compound 
of several ova. He does not suppose that these eggs undergo seg- 
mentation after deposition. JI am in a position to assert that the 
winter-eggs are formed in the Melicertw exactly like the summer- 
eggs, and that they are segmented after deposition absolutely like 
the latter. What may have deceived that eminent observer is, that 
the vitelline granules of the winter-eggs, being exceedingly opaque, 
render the stroma of the ovary which secretes them very dark. 
The first phases of the segmentation of the winter-egg are iden- 
tical with those of the summer-egg. It is difficult to follow the 
transformations in all their details, in consequence of the extreme 
opacity ; but the general course is exactly the same. As the deve- 
lopment progresses the ovum becomes less dark-coloured, until it 
finally acquires a lemon-colour, which it retains throughout the 
