Prof. E. Clapavede on the Reproduction of the Aphides. 363 



of all makes the germinal vesicle disappear in a homogeneous 

 vitellus. As to the mere fact of the persistance of the germinal 

 vesicle, it is, I admit, very difficult to arrive at perfect convic- 

 tion, because it is possible that the first nucleus, from which all 

 the nuclei of the blastodermic cells are produced by division, 

 might be itself produced spontaneously in the midst of the 

 vitellus some time after the (hsappearance of the germinal vesi- 

 cle. Therefore I do not venture to pronounce too absolute 

 an opinion upon this point; but in any case it is not true that 

 the vitellus is homogeneous at this period. On the contrary, it 

 contains numerous granules collaterally with the germinal vesi- 

 cle, as M. iMecznikow has very well shown ; and as regards 

 the formation of the blastodermic cells by gemmation at the 

 surface of the vitellus (Robin's theory), as represented by M. 

 13albiani, I do not know how we are to reconcile it with the 

 incontestable multiplication of the nuclei in the interior of the 

 vitelline mass — a phenomenon to which I have just alluded. 



The blastoderm formed surrounds the ovum, now become 

 pyriform, over its whole surface, except at the inferior pole, as 

 M. Mecznikovv and M. Balbiani describe. The portion of the 

 blastoderm in the neighbourhood of the inferior pole developes 

 into a sort of cylindrical process, which is soon detached by a 

 complete constriction, and separates from the embryo properly 

 so called. This body, seen by both M. Mecznikow and M. 

 Balbiani, has been very differently regarded by them. We 

 shall not take any notice of it, as it plays no active part in the 

 organogenic evolution. 



From this moment the embryo presents an oval form, and is 

 composed only of an external blastodermic layer and of a central 

 vitelline mass. J\I. Balbiani calls this mass a cell. I regret to 

 have to introduce here a discussion of words, but I cannot sub- 

 scribe to this denomination. No doubt the investigations of 

 MM. Briicke, Beale, Max Schultze, Hackel, and others have 

 compelled us to accept a singular transformation of the nature of 

 the word cell; but there is a long way from this to the confusion 

 introduced into scientific language by M. Balbiani, a confusion 

 to which I shall again have occasion to refer. With him, it 

 would appear, the word cell is to be applied in histology to 

 whatever has form ; whilst with all histologists who still employ 

 this term, the name cell can only be applied to a protoplasmic 

 mass, which, at least during part of its existence, is furnished 

 with a nucleus, with its well-known physical and chemical cha- 

 racters. Now the vitelline mass in question certainly has an 

 ovoid form, since it is bounded by the blastoderm; but it pos- 

 sesses no nucleus, and consequently can on no account merit 

 the name of cell. But we may pass over this technical point, 



