INDIVIDUALITY OF THE GERM-NUCLEI. 265 



in such a manner that each daughter cell receives exclusively 

 maternal or exclusively paternal chromosomes. The distribution 

 of each pair of homologous chromosomes is entirely independent 

 of that of every other pair, so that in the daughter cells com- 

 binations of non-homologous chromosomes occur regardless of 

 their parental origin; each daughter cell usually receives a mix- 

 ture of maternal and paternal chromosomes in varying propor- 

 tions. Within the limits of the reduced number, any combina- 

 tion of the chromosomes furnished by the immature germ cell 

 is possible in a daughter cell resulting from the reducing division, 

 save that a single daughter cell cannot receive both members of 

 a synaptic pair. Synapsis is thus explained by the provision 

 which it makes that two homologous chromosomes shall in no 

 case enter the nucleus of a single spermatozoon or mature egg 

 (Sutton, 1902). The principle of random distribution or inde- 

 pendent assortment of non-homologous chromosomes has been 

 confirmed by the direct observations of Carothers (1913 and 

 1917), Wenrich (1915 and 1916) and others. The point that 

 immediately concerns us here is the fact that in the reducing 

 division the individuality of the germ-nuclei is usually lost, for 

 it seldom happens that a single daughter cell, and consequently 

 a single mature gamete, receives exclusively maternal or exclu- 

 sively paternal chromosomes. 



"Synapsis is not a haphazard junction of chromosomes, but 

 an orderly union of elements of maternal and paternal origin, 

 similar in size, in details of form, and probably also in function" 

 (Kellicott, 1913, p. 294). The orderly processes of heredity as 

 they exist today in biparental organisms would be impossible 

 were the integrity of the maternal and paternal chromosome 

 groups not maintained up to the time of synapsis. In Crypto- 

 branchus allegheniensis and in some other forms this integrity 

 is manifested at every step by a complete segregation of maternal 

 and paternal chromosome groups; in other forms the inde- 

 pendence of the chromosome groups is maintained in spite of 

 the mingling of maternal and paternal chromosomes. The per- 

 sistent individuality of the chromosomes is the important thing, 

 and so long as this is maintained the germ-nuclei exist as actual 



