THE BEGINNINGS OF LIFE. 



209 



the ova of most animals, a new vesicular element which 

 is called the 'embryo cell/ This does not appear until 

 after the process of fecundation, and just anterior to. the 



FIG. 15. 



Segmentation of the Yolk after Fecundation, 

 a, b, c. Ovum of Ascaris nigrovenosa. (Kolliker.) 

 d. That of A. acuminata, showing later stage. (Bagge.) 



commencement of segmentation in the yolk mass. This 

 new cell, that which takes the place of the germinal 

 vesicle after fecundation, is generally tolerably distinct, 

 and nucleated, but Dr. Thomson says x : c In other 

 instances a clear spherule or space only is observed in 

 the place of the embryo-cell, and in a few animals no 

 clear part of this nature has yet been detected.' Here 

 then we certainly have the new evolution of a cell or 

 nucleus in the midst of the granular yolk-substance 

 after a fashion with which we are not unfamiliar 2 . But 



1 Loc. cit. p. 139. 



2 Much interest attaches to these facts. We see now, in respect of 

 the presence or absence of an embryo-cell, how close is the correspond- 

 ence between these reproductive units of higher animals and the spores 

 of Algae, Fungi, and Lichens, or the reproductive germs of the lower 

 Amcebx. In them also, as we have seen, the presence of a nucleus was 

 by no means invariable ; and in some of the cases where it did exist 

 (Hydrodictyon, Peziza, &c.) it also made its appearance, at first, as a mere 

 'clear space.' See note, p. 184. 



VOL. I. P 



