DEVELOPMENT IN CROSS-FERTILIZED EGGS 405 



on a cross between members of two different classes of Echino- 

 derms (5). 



It must be remembered that in speaking of normal processes 

 I refer only to the visible, morphological changes which follow 

 each other in orderly succession in the course of cleavage. This 

 cycle is uninterrupted and the changes themselves appear nor- 

 mal. If any deviations from the normal course of affairs are 

 present, they are far too shght to be recognized even in a very 

 careful study. 



In order to meet the possible objection that this characteris- 

 tic lagging and clumping is not typical of this and the foregoing 

 cross, I should perhaps emphasize the fact that the pecuHarities 

 described appear in every egg observed at this stage. That 

 it is not an artifact, due to poor fixation, is proved by the 

 fact that preparations of other crosses with the same egg 

 in which the same technique was used show^ normal anaphases 

 as consistently as these exhibit abnormal anaphases. If these 

 appearances were artifacts, we should not expect to find this 

 regularity in their occurrence. It should also be mentioned in 

 this connection that in all of the crosses with Fundulus eggs, the 

 eggs are taken from several females and placed in the same dish. 

 When the sperm is added the eggs are stirred about so that in 

 taking out a pipette full of eggs to fix it is certain that the eggs 

 are well mixed and that those fixed in any stage originate from 

 several females. The character, then, which determines the 

 behavior of the chromatin during the anaphase is not an indi- 

 vidual character, but is common to the species. 



S. Fundulus heteroclitus 9 X Menidia menidia notata cf 



The behavior of the chromatin in this cross has been described 

 by Moenkhaus (10), and the facts have become such a famiUar 

 part of our cytological knowledge that any further description 

 of the details of cleavage are unnecessary. My purpose in re- 

 peating his observations was to determine whether the condi- 

 tions he describes are common to all hybrid eggs of this cross. 

 My preparations resemble his descriptions and figures so closely 

 and so consistently that there is left no room for doubt that here 



