584: M. Coste on the Formation of Cells. 
and its total absence in others, form a serious impediment to the 
theory which locates the exclusive determining cause of all cell- 
formation in the pre-existence of this corpuscle. This also shakes 
the very foundations of the doctrine, and tends at the least to 
restraim its application. 
As regards the cytoblast or nucleus, M. Vogt has alread 
shown that it has no mfluence on the formation of the cell-walls 
of the embryo of the osseous fishes: I have been enabled to con- 
vince myself that the large diaphanous vesicles in the spinal cord 
of the Batrachia do not appear until after the production of the 
parietal membrane of these vesicles. 
But because the intervention of the nucleolus is not always 
necessary for the formation of the cells, and because the cyto- 
blast or the nucleus does not itself, im a certam number of cases, 
retain the function assigned to it by theory, must we necessarily 
conclude that the cells are never developed around a centre 
upon which the forming walls would mould themselves? Un- 
doubtedly we shall have frequent opportunities of observing 
limited masses of matter becoming coated with an envelope, and 
thus constituting the contents of the pouch which is formed at 
their periphery ; but we shall then remark, that in most of these 
cases this happens im a very different manner from what the theory 
supposes; for the matter which has constituted the centre, in- 
stead of being absorbed by the parietal membrane, to make room 
for the cellular contents subsequently introduced, itself forms 
the cellular contents, fills the cavity of the new cell, may there 
be applied to different prolonged functions, may live longer than 
the cell itself, or remain in reserve in the cavity of the latter, to 
serve the further purposes of nutrition or generation of new 
cells. The egg, im the two united vesicles of which it is com- 
posed, presents us with striking examples of a survival of the 
matter which has served as a generating centre, because we there 
see the germinative corpuscles persist when the parietal mem- 
brane which incloses them is dissolved, and take part in the new 
formations after it has been completely absorbed. The yolk 
there survives the vitelline membrane, and whilst the latter is gra- 
dually destroyed from the earliest period of its development, we see 
the yolk continue to nourish the embryo until after its birth. 
Such are the grave, numerous and decisive objections which 
arise against a doctrme, which must rather be considered as a 
bold invention of the mind than the carefully-considered expres- 
sion of satisfactory observation ; but although the bases of this 
doctrine are uncertain, it has not the less rendered an eminent 
service to science, because in the commencement it gave rise 
@ priori to the conception of the possibility that cells might 
be developed around a centre; and its influence has been very 
