CHROMATIN DEVELOPMENT AND HEREDITY 243 



pares his observations with those of Hacker ('95). The latter 

 investigator found in the cells of some species of Cyclops at 

 certain stages two nucleoli which, according to his interpretation, 

 represent the two parental chromatin masses. Since in Cyclops 

 the pronuclei do not fuse during fertilization and are closely 

 apposed, but structurally separate vesicles, as late as the two- 

 celled stage, and since the parental chromosomes remain bi- 

 laterally distributed, Moenkhaus accepts Hacker's view, but 

 hesitates to apply the same interpretation to the double nucleoli 

 in fish hybrids, and bases his objection upon the fact that in his 

 hybrids the pronuclei fuse during fertilization and that the 

 chromosomes do not remain distributed bilaterally upon the 

 spindle, but are mmgled indiscriminately at the end of the first 

 few cleavages. Miss Morris's observations are in agreement 

 with those of Moenkhaus as regards the mingling of the two 

 parental groups of chromosomes in the course of cleavage, but 

 she contends that a fusion of the germ nuclei does not occur. 

 I have also observed that there is a more marked grouping of 

 the two parental chromosome complexes in the second cleavage 

 stages of the reciprocal crosses between Fundulus and Cteno- 

 labrus than occurs in the fourth cleavage. 



However, the question as to whether in these double nucleoli 

 found in fishes we are dealing with parental homologues, is not 

 dependent upon the proof or disproof of the fact that the parental 

 chromatins remain segregated in the nucleus. If we are readj^ 

 to grant that the chromosomes maintain their individuality 

 throughout unlimited cell generations in other forms where there 

 is no hope of tracing any part of the chromatin through even one 

 cell generation, we cannot find objection to the idea that struc- 

 tures as closely related to the chromosomes as are these chromatin 

 nucleoli can reappear in connection with their respective spiremes 

 at certain phases of the nucleus. While perhaps the facts ob- 

 served by Moenkhaus do not argue directly in favor of such a 

 view, they cannot be considered as having any weighty bearing 

 of opposite significance. 



The facts presented here form strong evidence for the view 

 that these double nucleoli are correlated with the biparental 



