CHROMATIN — DEVELOPMENT AND HEREDITY 259 



drance to development. This is the case in the crosses with Cteno- 

 labriis cited here. 



On the other hand, if the cytoplasm be unfavorable to the 

 foreign spermatozoon as we conclude when early mitosis is fre- 

 quently abnormal, the foreign spermatozoon will not be able to 

 exercise its full effect against the egg nucleus. If the cytoplasm 

 of the egg succeed in suppressing the influence of the spermato- 

 zoon entirely, we may obtain normal embryos of the maternal 

 type. Thus we might have essentially parthenogenetic develop- 

 ment in the sense in which Loeb claims ('12), with the participa- 

 tion in mitosis of the paternal chromatin, if the hypothesis ad- 

 vanced above is true, that in fishes, the participation in mitosis 

 of the paternal chromatin partakes of the same nonspecific 

 nature as does the act of impregnation itself. 



There is as yet no proof that the nuclei of hybrid embryos of 

 the maternal type contain, unchanged, the ful number of 

 maternal and paternal chromosomes. Complete development 

 is so rare that, without proof, we cannot exclude the possibility 

 that a chance elimination of the right chromosomal elements — ■ 

 even the entire paternal complex — is responsible for it. The 

 character of mitosis in the cross, Ctenolabrus $ X Stenotomus cf 

 which gives many hatching embryos of the maternal type is 

 regarded as favoring the view that perfect development is cor- 

 related with normal mitosis. It may be that in cases where 

 abnormal mitoses prevail, very different conditions bring about 

 the same results. However it may be, whether the chromosomes 

 of the spermatozoon are completely eliminated or completely 

 retained, the result, the production of •a hatching embryo of the 

 maternal type, is comparable to the parthenogenetic develop- 

 ment of an egg. The chromosomes of the spermatozoon are 

 without influence. 



The objection might be raised here that complete recessiveness 

 of the paternal characters does not imply a complete loss in po- 

 tency of the paternal chromosomes. Newman's view on this 

 point has been mentioned in the introductory section of this 

 paper. If, however, the hybrids which are reared to hatching 

 still retain both parental nuclear components, it is unlikely 



