CHROMATIN — DEVELOPMENT AND HEREDITY 241 



suggests that the abnormal granular condition which occurs 

 irregularly in these hybrid eggs is caused by the dissolution of 

 the chromatin. Figure 40 shows one cell of a three-celled egg 

 in which the evidence points to the same conclusion. This 

 egg was included in a lot of eggs fixed in the eight-celled stage. 

 There is here evidence of lagging or eliminated chromatin. 

 There is also the same abnormally granular cytoplasm present 

 in the region of the spindle. Some chromatin masses are present, 

 but their outlines are indefinite. They are evidently in the proc- 

 ess of dissolution. These, as well as the lagging chromosomes, 

 are regarded as remnants of the first cleavage which, in this 

 case, was so irregular that further cleavage was impossible, an 

 interpretation which an examination of the remaining cells of 

 this egg seems to verify. One sister cell shows an anaphase 

 spindle with no recognizable Fundulus chromosomes, the third 

 cell contains three asters separated by masses of granular proto- 

 plasm and lacking anything that can be identified as chromatin. 

 In this case the dissolution of chromatin is clearly associated 

 with a cessation of development, and it is highly improbable 

 that any of the eggs in which extensive degenerative changes of 

 this nature occur in the early stages survive. It would be of 

 interest to know whether normal eggs, when fertilized in the 

 laboratory, are ever subject to disturbances of the same kind 

 or whether the effect is a result of hybridization. Its signifi- 

 cance in this connection lies in the possibility that it may occur 

 at any time during development and in varying degrees, and 

 that in later stages, after cleavage has proceeded for some time, 

 its effect might not be so widespread and therefore less disastrous. 

 The later cleavages were studied in eggs belonging to the same 

 lot as that shown in figure 26. These had developed for nearly 

 sixteen hours. The conditions in them varied, some eggs showing 

 cells more uniform in size, arrangement, and nuclear character 

 than others. Figure 41 is from a hybrid blastoderm in which 

 seventeen mitotic figures were counted. No abnormalities were 

 noted in any of them. In a thirteen-hour egg of the pure breed 

 twenty-five normal anaphase figures were found. Figure 42 

 shows several of these, from which it is evident that the polar 



JOURNAL OI' MORPHOLOGY, VOL. 31, XO. 2 



