

FIG. i. 



CHROMOSOME GROUP IN BRACHYSTOLA MAGNA. 25 



ously described as the last generation of primary spermatogonia), 

 lie in the follicle without definite arrangement and are usually 

 much flattened and distorted by mutual pressure and that of the 

 growing spermatocysts between which they lie. For this reason 

 a study of the chromosome series is difficult in this cell-genera- 

 tion, but, fortunately, I have been able 

 to find a few division-figures which per- 

 mit of an accurate study of the chro- 

 mosomes. Such a cell as that shown in 

 Fig. i a metaphase in polar view- 

 offers the best opportunities. Here it is 

 apparent at a glance that the chromo- 

 somes are of a variety of sizes, but yet 

 in general so nicely graded as to form 

 an almost regular series from smallest to 

 largest. A second glance, however, 

 reveals the fact that there is one very 

 prominent break in this graded series, 

 separating the six smaller chromosomes 

 from the remaining larger ones, and a 

 count of the larger group shows it to 

 contain seventeen units, giving as a total 

 the odd number twenty-three. 1 The odd 

 or twenty-third member of the group, 

 as can be plainly seen in the following 

 division, is the accessory chromosome, 

 which on account of its peculiar be- 

 havior will be considered separately. 

 There is, therefore, in the ordinary group, 

 the even number, twenty- two. More 

 especially in the smaller group, but like- 

 wise in the members of the sixteen, it 

 can be seen that the gradations in volume 



are not between individual chomosomes but between pairs, the 

 two members of which in each case are of approximately equal 



1 Montgomery (/. c. ) has found four of the Hemiptera-heteroptera to possess an 

 odd somatic number of chromosomes and I have observed the same to be true for some 

 fifty species of Acrididse and Tryxalinse. 



FIG. i. Polar view of 

 metaphase of first genera- 

 tion of secondary spermato- 

 sonia. Six small chromo- 



o 



somes designated by letters 

 i,j and k. (From section. ) 

 Note. All figures given in 

 this paper are camera lucida 

 copies of the portions under 

 consideration from the orig- 

 inal camera drawings to be 

 published in the forthcoming 

 work to which this is pre- 

 liminary. The figures are 

 not schematized. 



