BEHAVIOR OF CHROMATIN IN HYBRIDS 509 



figure 21 the same stage for the hybrid; while figures 22 and 23 

 represent the nuclei of the completed 2-cell stage in hybrid and 

 normal eggs respectively. 



Figure 24 represents the prophase of the second cleavage in 

 a hybrid Fundulus egg. It will be seen that there is here, as in 

 a normal egg, a single mass of chromatic material on the spindle 

 quite different from the double mass formed by the un- 

 united germ-nuclei before the first cleavage. This is added 

 proof that in the nuclei of the 2-cell stage, the paternal and 

 maternal chromatin is mingled. That the types of chromosomes 

 do not, however, lose their identity is shown by the fact that in 

 the later stages of the second cleavage they appear as distinctly 

 as they did in the first cleavage (fig. 25). Throughout the later 

 cleavage, moreover, the resting nuclei and prophases of hybrid 

 eggs are indistinguishable from those of the normal ones, while 

 the hybrids continue to show the two types of chromosomes in 

 the anaphase stages. Figures 27 and 28 and figures 29, 30, 31 

 and 32 illustrate this fact. Figure 27 is of a fourth cleavage 

 spindle and figure 28 of a sixth, while the others are from 12-hour 

 stages. 



With such figures as these last ones before us we should hardly 

 look for any considerable ehmination of chromatin in the early 

 stages, and in fact there is no evidence that the paternal chroma- 

 tin is thrown out in these hybrids. Figure 26 shows the pro- 

 phase of the fourth cleavage in a hybrid, and in this a small mass 

 of chromatin is found outside the spindle, but there is no evi- 

 dence that this is of paternal origin. This is the only case of 

 such abnormality I have found in the early cleavages, and the 

 evidence of the later stages leads one to think that the paternal 

 chromatin is generally retained and divides normally. 



The first appearance of abnormality that can be called general 

 is in the 12-hour stage. Here we find often, in the middle of 

 the blastoderm, large cells with irregular nuclei, in which there 

 has evidently been a failure to divide normallj^ Figure 34 

 shows such a cell, and figure 33 two more, with a few normal 

 cells drawn for comparison. But even here we cannot say that 



