CH. X] MODIFICATION OF CLEAVAGE 105 



A*-B 2 . The products of these nuclei we may call B 1 B 2 , 

 B 3 -B 4 . The following division will give eight nuclei, GMT 8 , 

 and at the sixteen-cell stage we may call the nuclei C^-D 1 , 

 C 2 -D 2 , etc., as shown in the accompanying diagram. 



Xow let us compare, using this nomenclature, a normal egg 

 (Fig. 33, B) with an axially compressed egg (Fig. 33, A). In 

 the normal egg at the sixteen-cell stage, the nuclei around the 

 upper pole will be CM) 1 , C 3 -D 3 , C 5 -D 5 , C 7 -D 7 , and those 

 around the lower pole, C 2 -D 2 , O-D 4 , C 6 -D 6 , C 8 -D 8 . On the 

 other hand, in a compressed egg that has been freed from the 

 compression after the eight-cell stage, so that the fourth fur- 

 row has come in horizontally (Fig. 33, A-D), we find that the 

 nuclei in the upper hemisphere are C^-C 2 , C 3 -C 4 , C 5 -C 6 , C 7 -C 8 , 

 and in the lower hemisphere, D^D 2 , D 3 -D 4 , D 5 -D 6 , D 7 -D 8 . 

 Thus there is an entirely different distribution of the products 

 of the nuclear division in the two cases, 1 yet normal embryos 

 develop from both eggs. 



The simplest and most obvious conclusion from this result is, 

 I think, that the sequence of nuclear division during the early 

 cleavage-period has no relation to the subsequent formation 

 of the embryo, and that at this time the nuclei are all equiva- 

 lent. 



1 There are several other possible combinations of these sixteen nuclei, but in 

 no case is the distribution alike in the normal and in the comi 



