634 



germ cells. The ovocytes and spermatocytes of the first order have on 

 the contrary half this normal number, and so does the mature ovotid 

 or spermatid. How then does it come about that Prof. Haecker finds 

 in the mature egg on-quarter the normal number of chromosomes? 

 For that must be the case if the somatic cells contain each 24 and the 

 ovotid 6. Again, why should Rücke rt, and Prof. Haecker himself in 

 his earlier contributions, have entirely overlooked the double nature 

 of the chromosomes of the ovotid, if they are double (bivalent) as Prof. 

 Haecker now concludes? If there is any particular conclusion of 

 which cytologists can feel reasonable certain , it is that the chromoso- 

 mes of the mature germ cell are univalent and in half the normal 

 number. 



The »Gedankengang« which has apparently led Prof. Haecker 

 to his present standpoint in regard to the maintenance of the separate 

 grouping of the paternal and maternal chromosomes in the germ cells, a 

 condition first pointed out byRiickert (1895) and since corroborated 

 by a number of observers. Long before this it had been shown by 

 van Beneden (1883) for the early cleavages oî Ascaris. This is most 

 marked in the early cleavages, both the gonomerity of the nuclei and 

 the vesicular separateness of the chromosomes. The fertilized egg has 

 an equal number of chromosomes of its own (maternal chromosomes) 

 and of chromosomes (paternal) indroduced by the spermatozoon, as 

 van Beneden first showed (1883). These keep in two groups during 

 the earlier cleavages. According to my results (1901), in opposition to 

 Prof. Haecker, just after the last spermatogonic division each pa- 

 ternal chromosome pairs with a maternal one; and from the time of this 

 conjugation up to the stage of another fertilization there can be no 

 maintenance of two distinct groups of chromosomes. For this pairing 

 means the closest union of the two sets of chromosomes. As I pointed 

 out in my last paper (1904) in the last generations of spermatogonia 

 of Urodelea there is certainly no separateness of the maternal and pa- 

 ternal elements, for it is very probable that in the chromatin spirem 

 of the prophase of the last generation of spermatogonia each paternal 

 chromosome is contiguous to the maternal chromosome with which it 

 will conjugate in the daughter cell. Therefore it would be probable 

 that the two gonomeres are most distinct in the earliest stages, while 

 in later generations of the germ cells this division of the nucleus of a 

 germ cell into a maternal and a paternal half gradually becomes obli- 

 terated. At one end are the two completely separate pronuclei before 

 the first cleavage; at the other the close union of maternal with pa- 

 ternal chromosomes in the synapsis stage. 



From these observations of my own, now being corroborated by 



