508 MARGARET MORRIS 



chromosomes have begun to separate. In this case the types 

 are grouped, the male chromosomes lying on one side and the 

 female on the other side of the spindle; but this is not always the 

 case. Figure 8 shows chromosomes from a similar stage in which 

 the two types are mingled. 



In the later anaphase the difference is still more evident. Here 

 I find, as did Moenkhaus, that the foreign chromosomes some- 

 times lag behind the normal ones in going to the poles. Figures 

 12 and 17 show the anaphase of the first cleavage in two hybrid 

 eggs, while figures 13 and 18 give the same stage for the normal 

 eggs. The difference between the hybrid and normal eggs is dis- 

 tinct and constant except in the case shown in figure 19. This is 

 draw^n from an egg found on a slide that was supposed to have only 

 normally fertilized eggs on it ; but it is more reasonable to suppose 

 that, by a mistake in the handling of the preserved material, a hy- 

 brid egg was included among the normal ones than that one nor- 

 mal egg should present an appearance so like the hybrids and so 

 different from all the other normal eggs. Figures 14 and 16 show 

 the chromosomes from the metaphase of the first cleavage of two 

 hybrid eggs, drawn with a magnification of 2500 diameters. They 

 should be compared with the corresponding stage in a normal egg 

 which is represented in figure 15. Even in the smaller-scale draw- 

 ings, the difference between the two chromosome groups is appar- 

 ent, but in the figures drawn with the higher magnification the 

 distinctions between two types are particularly apparent. 



The telophase of the first cleavage in these hybrids is very 

 much like the corresponding stage in the normal egg. The vesi- 

 cles in some cases fuse a little more slowly as the foreign chromo- 

 somes have lagged a little in going to the poles; but the differ- 

 ence is slight, and by the time the asters have separated and 

 come to a polar position preparatory to the second cleavage, the 

 nuclei of hybrids and normals cannot be distinguished from each 

 other. In both cases one can see traces of the vesicles in the 

 nuclear reticulum: and this is the case in the resting nuclei of 

 both hybrid and normal eggs throughout development. Figure 

 20 shows the telophase of the first cleavage of a normal egg, and 



