Ch. X] MODIFICATIOX OF CLEAVAGE 105 



A^-1j2. The products of these nuclei we may call B^-B^, 

 B'^-B*. The following division will give eight nuclei, C^-C^, 

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

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



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

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

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

 upper pole \^'ill be C^-B\ C^-D^, C^-D^, C'-Ds and those 

 around the lower pole, C2-D2, C^-DS C^-T)% C^-DS. On the 

 otlier 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^ C^-C*, C^-C^, C'-C^, 

 and in the lower hemisphere, D^-D^ D^-D*, D^-D^, D'-DS. 

 Thus there is an entirely different distribution of the products 

 of the nuclear division in the two cases,^ j'et 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 otiier possible combinations of these sixteen nuclei, but in 

 no case is the distribution alike in the uomial and. in the compressed egg. 



