SEX AND HEREDITY 



469 



chromosome of each pair passing to one pole, the other to the other pole 

 of the first spindle (VI.). There is, in fact, a sorting of the members 

 of the several pairs to constitute the new nuclei, the number passing 

 to each being half of the total. Thus, if there were 2x chromosomes 

 in the nucleus of the mother-cell, each of the new nuclei would 

 consist of only x chromosomes. If, as there is good reason to 

 believe, the chromosomes in some way represent or convey heredi- 

 tary qualities, then by this reduction- division, or meiosis as it has 

 been called, those qualities will be segregated into two groups, and the 

 daughter-nuclei will not be functionally the equivalents one of another. 



The difference between this and a somatic division may be 

 illustrated by a diagram. If a simple case be taken, with six as the 



FIG. 394. 



A, Diagram illustrating the behaviour of the chromo- i 

 somes in somatic division, when the number of chromosomes > 

 is six. (After Strasburger.) 



B, Diagram showing the behaviour 

 of the chromosomes iaJfleio-fls. where 

 the number six is reduced to three by 

 segregation into two groups. (After 

 Strasburger.) 



diploid and three as the haploid numbers, and the specific qualities 

 of the individual chromosomes be indicated by differences of shading, 

 then Fig. 394 A, a, b might represent what happens in a somatic division. 

 Each chromosome being halved, and the halves diverging to either 

 pole, each new nucleus there formed will have an equivalent repre- 

 sentation of each chromosome, with the qualities which it bears. But 

 in the reduction-division, since the chromosomes pair and separate 

 again, and since three of these converge as whole chromosomes 

 to each pole, it is clear that the two new nuclei will not have an 

 equivalent representation of the qualities of all the six chromosomes, 

 but only of three of them (Fig. 394 B, a, b). The meiosis, or reduction- 

 division, has segregated them into two groups. This is the essential 

 point in the first or heterotype stage in the tetrad-division. The 

 second stage is a homotype division, that is carried out like any somatic 

 division, and the nuclei of each resulting pair will be equivalent one 

 to another. Thus in each tetrad there will be two cells or spores of the 



