INDIVIDUALITY OF THE GERM-NUCLEI. 255 



process which I have been able to follow in considerable detail, 

 but will not attempt to describe here. About this time the 

 centrosphere or "attraction sphere" divides. 



During the anaphase and early telophase the maternal and 

 paternal chromosome groups are almost always clearly separated, 

 sometimes with a broad space between the two groups. The 

 segregation of the chromosomal vesicles into two groups, maternal 

 and paternal respectively, is usually evident. In the late telo- 

 phase the chromosomal vesicles of each group unite to form 

 separate nuclear vesicles which for a time show indications of 

 their manner of origin through the persistence of lobes separated 

 by deep clefts. The inner boundaries of the chromosomal 

 vesicles persist for a time as partitions in the nuclear vesicles, 

 but finally disappear wholly or in part. In the late blastula the 

 vesicular nucleus in many cases retains a lobed structure through- 

 out the resting stage. It is possible that in some cases the fusion 

 of chromosomal vesicles to form vesicular nuclei of the usual 

 duplex type is never completed, for in the late blastula and 

 early gastrula nuclei consisting of three, four or even more well- 

 rounded vesicles are not uncommon. 



How much longer and to what extent during the development 

 of the embryo a strict separation of the germ-nuclei is maintained 

 I have not attempted to determine, but it is not necessary to 

 conclude that it continues throughout the life of the organism, 

 either in the somatic or the germ cells. In the discussion it will 

 be shown that the individuality of the germ-nuclei is not in- 

 compatible with a mingling of maternal and paternal chromo- 

 somes, and there is no biological necessity for a strict separation 

 of the germ-nuclei in any stage from fertilization to synapsis. 



DISCUSSION. 



In 1875 Oscar Hertwig and Hermann Fol showed that the 

 fertilized egg contains two nuclei, one belonging to the egg itself 

 and the other introduced by the spermatozoon. While the 

 earliest observers of the process of fertilization, notably Auerbach, 

 Strasburger and Hertwig, described the complete fusion of these 

 germ-nuclei to form the first embryonic nucleus, called by 



