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1 



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 



a 



Fig. 15. 



Segmentation of the Yolk after Fecundation. 



a, h, c. Ovum oi Ascaris ?iigrovenosa, (KoUiker.) 



d. That oi A, acummata, showing later stage. (Bagge.) 



F 



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 ^ :— 



^ 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 



^ Log. cit. p. 139. 



^ 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 

 Amoeba;. 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 

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

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



VOL. L 



P 



