448 
POPULAE SCIENCE EEVIEW. 
germinal cell appeared to all anatomists who do not believe 
the Aphis germ-mass to be transformed cell elements derived 
from an egg so serious an objection to the doctrine of Par- 
thenogenesis that it has always met with opposition. Thus 
Carus considered that the formation of an embryo from a 
mere granular germ-mass could not be essentially the same 
process as the development of an embryo from an egg by 
segmentation of its yolk-mass. And Quatrefages particularly 
emphasizes the absence of the germinal vesicle as equiva- 
lent to the absence of any real ovum. The disappearance 
of the germinal vesicle prior to the first changes induced 
by fecundation is, however, as Quatrefages expressly urges 
(and therein he is confirmed by all recent authorities), an 
established fact, and may explain why the continued presence 
of germ vesicles would be difficult to discover amongst the 
rapid movements of evolution going on in the Aphis germ- 
mass derived by cellulation from an original egg. As to the 
part which the yolk segmentation takes, it belongs essentially 
to the nutritive function of the ovum being influencedj but 
not caused , by fertilisation. According to Robin (Journ. de 
TAnatomie, vol. v.), the embryonal blastoderm of the insect 
(he instances the orders Dipt era, Hymenoptera, and Coleoptera) 
is formed at the expense of the transparent portion of the yolk 
substance, not by its progressive segmentation (which does 
not, in fact, produce cells proper), but by “ gemmation / 9 
and this interpretation Robin applies to the Articulata gene- 
rally. “ There are,” he says, “ beings in whom the blasto- 
dermic cells appear by gemmation , attaining at once to the 
constitution and properties proper to them during their indi- 
vidual existence ; and there are other beings in which the 
blastodermic cells arrive only gradually at the condition of 
individuality of form, size, and properties, by passing through 
the intermediate phases of yolk, globules, progressive segmen- 
tation, to become finally blastoderm.” On the other hand, 
Leydig, in his account of viviparous Aphis development, 
draws and describes cellular elements — one larger cell in the 
middle of a group of smaller ones, imbedded in a fine granular 
substance, passing from chamber to chamber of the ovarian 
tube. The large cell (germ) becomes in the third chamber 
surrounded by a mass of fine cells, the whole then resembling 
the usual appearance of a developing egg. He considers the 
viviparous larva as much the product of cell development as if 
it had sprung directly from an ovum. Huxley has described 
the ovum of the oviparous Aphis in its embryonic state as an 
isolated germinal vesicle with distinct germinal spot, which, in 
the third chamber, is surrounded by the vitellus, the ger- 
minal S]fot remaining still clearly distinct. In the viviparous 
