- M. Coste on the Formation of Cells. 95 
should be found in those parts where the matter undergoes that 
primary elaboration which prepares the materials of the new in- 
dividual. Hence the bases for.its solution must be sought in the 
metamorphoses of the vitellus, and we there find the facts deve- 
loped in so characteristic and evident a manner, that they may 
be verified by any one. But, before showing how it is that the 
amorphous matter assumes the cellular form, there is another 
condition of that matter, the history of which I shall rapidly 
trace, and with which it is not less important.to be acquainted. 
I allude to that progressive subdivision by means of which it is 
employed for the production of organic spheres, which must be 
considered hereafter as special elements of the living tissues. We 
shall proceed then, first, to study the mode of generation of these 
spheres in the vitellus of Mammalia, subsequently tracing it 
wherever it occurs. When, in Mammalia, the seminal fluid has 
passed through the uterus and reached the Fallopian tubes so 
as to envelope the ovum with its moving molecules, in propor- 
tion as the molecules penetrate its substance, we see the yolk 
undergo the primary modifications which are about to induce the 
organization of the germ. It commences by becoming concen- 
trated into a smaller volume, and forming itself into a granular 
globe so perfectly spherical and correctly outlined, that all the 
grains of which this globe is composed, and which are united 
together by means of a viscid diaphanous fluid, are apparently 
retained in the general form which their assemblage represents, 
by a delicate layer of the same fluid which appears at the peri- 
vhsty as the representative of an enveloping membrane. But if, 
after having sufficiently guarded against optical illusions, we en- 
deayour to develope the reality of the appearances which obscure 
it, we soon recognise that such a membrane does not exist, and 
that those observers, as for instance Barry, who have admitted its 
existence, have not pursued their examination with sufficient care. 
Their error here evidently arises from their having considered the 
superficial part of the viscid matter which retains the granulations 
mingled in its own substance as an enveloping membrane. This 
matter is in fact merely lodged in the interstices of the granu- 
lations which it agelutinates, and which it separates so regularly 
that it appears at first sight to form a wall at the periphery of the 
vitellus, the outline of which appears more distinctly delineated 
in proportion as its transparence contrasts with the opacity of the 
anulations which it bounds. But, I repeat, this is an illusion 
which an attentive analysis corrects, ‘and on this point I have suf- 
ficiently repeated my observations to have a well-founded con- 
viction. 
The vitedlus is not then, as has been supposed, a vesicle or cell 
filled with granules, but simply a granular homogeneous sphere, 
