EARLY STAGES OF DEVELOPMENT OP THE RABBIT. 123 



the ova which became fertilised and developed into normal 

 embryos. 



The corpora lutea are often very difficult to make out at 

 this early stage, but I am pretty certain that there were cer- 

 tainly not more than five corpora lutea in one ovary and six in 

 the other. 



Fig. 9 is drawn from one of the fertile ova of this rabbit. I 

 have reproduced it here to show the appearance of the denser 

 inner and clearer outer layer of protoplasm of each sphere, de- 

 scribed above as occurring in the earlier stages. 



Possibly this appearance is constant in later stages, but as 

 the cells get smaller the difference becomes less easy to distin- 

 guish. 



I have avoided the use of the terms macrosphere and micro- 

 sphere, because a morphological significance is sometimes given 

 to these terras which I think is not advisable, at any rate in the 

 case of the rabbit. 



At the same time it is necessary, in discussing van Beneden's 

 description and deduction, to pay especial attention to the 

 question of the fate of the segments derived from the two first 

 spheres. 



It is hardly necessary to point out the very great difficulty 

 in determining the fate of the descendant segments of the two 

 primary segments when size is the only character on which we 

 can rely, and when even in size there may be no difference. 

 Again, if the ovum may sometimes divide into two segments 

 of different size, may not the two primary segments also 

 segment unevenly? 



I can see no way of determining the question except by 

 watching the division of one specimen, and this is, as far as I 

 have tried, impossible. Even if it were accomplished, it must 

 be under conditions which can hardly be called normal, and 

 therefore not a very safe ground on which to base either facts 

 or theory. 



Certainly, in cases where the primary division is so unequal 

 as in fig. 3, the subsequently formed segments could, on the 

 whole, probably be classed as larger ones derived from the 



