CHROMATIN DEVELOPMENT AND HEREDITY 249 



the new cleavage plane. The cell is m the telophase. Figure 69 

 shows one or two chromosomes still at the equator when those at 

 the poles have begun to form vesicles. Figures 65 and 66 show 

 chromatin persisting in the axis of the former spindle. Figure 

 65 is of a prophase, viewed laterally. This may be an active 

 extrusion of nuclear material, but the fibers which accompany the 

 extra nuclear chromatin in this case extend to the first cleavage 

 plane and seem to be persisting structures rather than new out- 

 growths from the aster. Figure 66 is from a two-celled egg in 

 the metaphase, viewed from the poles. The figure was recon- 

 structed from two sections. Several chromosomes lie along the 

 fibers connecting the sister spindles. Here again the appearance 

 resembles a structure persisting from the previous cleavage rather 

 than one originating during the present division. The apparent 

 interference in the completion of the dividing cell wall strengthens 

 this impression. 



The active process of elimination (during the metaphase) 

 as described for the cross Fundulus heteroclitus 9 X Ctenola- 

 brus adspersus cT has been observed frequently in this cross. 

 Figure 64 shows it in its less exaggerated form. This is un- 

 doubtedly one of the conditions which leads to lagging in the 

 anaphase. 



Figure 72 is of a section through the blastoderm of an egg 

 which had developed for five and one-half hours. Such blastoc- 

 derms frequently show large numbers of dividing cells, in all of 

 which the character of mitosis is essentially similar to that of 

 the earlier divisions. Figure 73 illustrates some of the typical 

 abnormalities. In figure 74 is shown a section through a blasto- 

 derm in which the nuclei were in the resting stage. Here it is 

 difficult to determine whether chromatin has been eliminated, 

 since the eliminated chromatin does not persist in such form that 

 it can be recognized easily. Small nucleus-like inclusions be- 

 tween the cells of the otherwise normal-appearing blastoderms 

 may be the remains of chromatin which has been left in the equa- 

 torial plane. Such masses are shown in figure 75. Chromatin 

 remainmg in the cytoplasm is evidently rapidly absorbed. 



