238 EDITH PINNEY 



of the chromosomes of the two species is maintained throughout 

 the first four cleavages. Any change in size is relative and 

 affects alike the native and the foreign chromatin. The syn- 

 thetic processes which result in the growth of the chromosomes 

 are evidently common to both groups, any differences that may 

 exist being beyond the limits of ordinary observation. 



On account of the larger bulk of the Fundulus chromosomes, 

 there is here, too, an increased demand on the cytoplasm of 

 the egg for the production of more chromatin than is required 

 in the straight fertilized Ctenolabrus eggs. The possible effect 

 of such a drain on the resources of the egg will be considered 

 later. 



In the great majority of cases observed, no lagging occurred. 

 All of the anaphase stages of the reciprocal cross which were 

 figured by Miss Morris show lagging chromosomes and form a 

 striking contrast to the conditions found here. In this respect 

 the crosses between Fundulus and Ctenolabrus show a difference 

 in behavior comparable to that shown by the reciprocal crosses 

 between Fundulus and Menidia studied by Moenkhaus. In 

 the latter case, however, it was when Fundulus was used as the 

 sperm parent that lagging occurred, while in the case described 

 here, the lagging occurs when Fundulus is used as the egg parent. 

 The degree of difference may not be as great in the Fundulus and 

 Menidia crosses as it is in the crosses between Fundulus and 

 Ctenolabrus, although figure 23 of Moenkhaus's paper shows 

 marked lagging. 



The crosses with Ctenolabrus clearly demonstrate that this 

 lagging is not due to differences in the cleavage rate, as might 

 be concluded from the crosses with Menidia. In all of the 

 heterogeneous crosses so far studied the rate of cleavage is that 

 characteristic of the egg species. The case under consideration 

 is an additional and striking illustration of the same fact. The 

 Fundulus chromosomes in the egg of Ctenolabrus divide twice 

 as rapidly as they do in their normal environment. The effect 

 of the Ctenolabrus egg in accelerating the division rate of the 

 chromosomes carried in by the Fundulus spermatozoon is more 

 impressive than the opposite retarding effect of the egg of Fundu- 



