DEVELOPMENT IN CROSS-FERTILIZED EGGS 403 



distributed in the first anaphase, as well as in subsequent divi- 

 sions. Figures la and lb are from an egg in the first cleavage, 

 as are also figures 2a and 2b. Figure 3, a and b, and figure 4 

 show the anaphase of the second cleavage. The conditions 

 displayed here are so typical for all of the sections studied that 

 it seemed superfluous to multiply the evidence by many draw- 

 ings of practically the same thing. The only variation between 

 first anaphase spindles in these eggs is in the amount of undivided 

 chromatin which lags at or near the equator. This variation 

 indicates that, whether chromatin is actually eliminated or not, 

 and there is much reason to think that it is, the foreign chroma- 

 tin which does remain in the egg is distributed in a variety of 

 ways. Undivided chromosomes can pass to one pole only and, 

 therefore, one of the first two blastomeres lacks some chromo- 

 somes which the other contains. Thus extreme variation between 

 blastomeres arises and is increased during early cleavage. It 

 is a significant fact that the behavior of the chromatin during 

 the first anaphase is duphcated during the second cleavage. 



Perhaps a word might be added here in description of the 

 lagging masses of chromatin. Those which are nearer the daugh- 

 ter groups of chromosomes resemble in contour and size the 

 smaller chromosomes of the foreign species (15). Other masses, 

 usually lying on or near the equator of the spindle, cannot be 

 reconciled with single chromosomes of either species. They 

 resemble more nearly the undivided chromosomes of the early 

 metaphase stages. Some of the masses show rod-like projec- 

 tions which suggest that perhaps two or even more chromosomes 

 have adhered to each other during their partial journey to the 

 pole. The appearance may be due, however, to nothing more 

 than a collision such as frequently occurs in normal anaphases. 

 Figure 3a shows what is plainly a spHt chromosome, the halves 

 of which are still adherent, passing to one pole. I have yet to 

 observe an anaphase figure in this cross at these early stages in 

 which there is no lagging chromatin. 



JOCBNAL OF MORPHOLOGY, VOL. 



