CHROMOSOME GROUP IN BRACHYSTOLA MAGNA. 35 



comparable to that existing between mother- and daughter- 

 cells. 



I have endeavored to show that the eleven ordinary chromo- 

 somes which enter the nucleus of each spermatid are selected 

 one from each of the eleven pairs which made up the double 

 series of the spermatogonia. It now becomes a highly interest- 

 ing question whether there exists in the ripe egg a graded series 

 of chromosomes similar to that of the mature male element. I 

 have found the chromosome group not only of the oogonia but 

 also of the ovarian follicle cells (Fig. 1 1) to correspond perfectly 

 with that of the spermatogonia ; and if we are permitted to assume 

 that the reduction process in both sexes is the same, we have no 

 alternative but to believe that the chromosome series of the 

 mature germinal products also are alike. Obviously, copulation 

 of such nuclei in fertilization would restore the conditions which 

 we have found not only in the early germ-cells but in some out- 

 side the line of succession. 



These latter observations have totally disregarded the accessory 

 chromosome, but it is in it, if further research shall substantiate 

 my present limited but thoroughly consistent results, that we 

 shall find our most unequivocal evidence of chromosomic indi- 

 viduality. We have noted that the spermatogonia have twenty- 

 three chromosomes, and that the odd one of these is the acces- 

 sory which by means of its idiosyncrasies may readily be 

 recognized in all except the active mitotic stages. We have also 

 noticed that this element is unequally distributed in the maturation 

 divisions and as a consequence occurs in exactly half the sperma- 

 tozoa. In the oogonia and ovarian follicle-cells in which I have 

 been able to count the chromosomes, I have found but twenty- 

 two ; and the fact that none of these behaves in the characteristic 

 manner of the accessory proclaims it the missing member. 



We should expect therefore to find but one kind of mature ova 

 in respect to number of chromosomes while we know that by 

 the same standard there are two kinds of spermatozoa. Obviously, 

 then, the number of chromosomes in the cleavage-nucleus of the 

 fertilized egg (twenty-two or twenty-three) must depend upon the 

 number introduced in the sperm-nucleus, since the latter con- 

 tains either eleven or twelve, according as the accessory chromo- 



