384 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 

 restrain its application. 



As regards the cytoblast or nucleus, M. Vogt has already 

 shown that it has no influence 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, in a certain 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 w^alls 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 in 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, in 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 doctrine, 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 

 a priori to the conception of the possibility that cells might 

 be developed around a centre ; and its influence has been very 



