INDIVIDUALITY OF THE GERM-NUCLEI. 259 



dence supporting the view that in these double nucleoli observed 

 in fishes we are dealing with parental homologues. 



Concerning Cryptobranchus allegheniensis, the writer believes 

 that the observations recorded in the present paper establish 

 beyond question the complete separation of maternal and pa- 

 ternal germ-nuclei to a late blastula stage at least. The separa- 

 tion is particularly marked during the resting stage of the nuclear 

 cycle, precisely where most investigators working with other 

 species have encountered the greatest difficulty. 



The observations thus far cited indicate that in certain forms 

 the individuality of the germ-nuclei during early embryonic 

 development is maintained by complete separation of the nuclear 

 material derived from the egg and the spermatozoon respectively. 

 It has already been indicated that this segregation is not by any 

 means a universal phenomenon. Is it possible that the indi- 

 viduality of the germ-nuclei may be maintained, in all essential 

 respects, in those other cases where there is a mingling of chro- 

 matin derived from the two germ-nuclei? Let us first examine 

 the facts that require explanation. 



In all cases where the germ-nuclei fuse into a single vesicular 

 nucleus before the formation of the first cleavage spindle, mingling 

 of maternal and paternal chromosomes may be expected. Sax 

 (1918) has recently described two cases in flowering plants, 

 Fritillaria .and Triticum. In Fritillaria the germ-nuclei usually 

 unite while in the resting condition, although occasionally they 

 are in the spireme stage at the time of fusion. The presence 

 of a single spireme in the zygote could not be demonstrated. In 

 Triticum the sperm-nucleus is small and almost homogeneous in 

 structure even while in contact with the egg nucleus. The 

 sperm-nucleus enters the egg-nucleus and there forms a separate 

 compact spireme; at the same time the spireme of the egg- 

 nucleus is formed. In both Fritillaria and Triticum the maternal 

 and paternal chromosomes are formed independently, but they 

 are not found in separate groups. 



Moenckhaus (1904) found that after the first few cleavage 

 divisions in his hybrid teleost eggs the chromosomes of maternal 

 and paternal origin mingled indiscriminately upon the equatorial 



