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- 

 phery as the representative of an enveloping membrane. But if, 

 after having sufficiently guarded against optical illusions, we en- 

 deavour 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 agglutinates, 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 

 granulations 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 vitellus is not then, as has been supposed, a vesicle or cell 

 filled with granules, but simply a granular homogeneous sphere, 



