570 FERNANDIJS PAYNE 



cells with 12 chromosomes and two with 13 in the first division; 

 in the second division, 20 counts showed 12 in all. From 12 

 counts of the first division in specimen 27-4, there were four with 

 12 chromosomes, three with 13 and one with 14. In the second 

 division 22 counts were made. Fourteen of these showed 12 

 chromosomes, seven showed 13 and one showed 14. 



Specimens 3^-1. Stevens ('10) accounted for the occasional 

 appearance of 13 chromosomes in the second division by suppos- 

 ing that the small idiochromosome sometimes divides precociously. 

 In this specimen the evidence is in favor of a similar interpretation. 

 Only four first division figures which could be clearly counted 

 were present. All of them contained 12 chromosomes (fig. 5, 

 I and /). In the second division, 125 counts gave 115 with 12 

 chromosomes and 10 with 13. If the 12-group is studied care- 

 fully, it can be seen that there are four chromosomes which are 

 noticeably smaller than the others (fig. 5, A, B, C, Z>). A fifth 

 one is present which sometimes appears about the size of these 

 four, but more often it is just a little larger, intermediate be- 

 tween them and the larger chromosomes. In the 13-group five 

 and sometimes six chromosomes are smaller than the others 

 (fig. 5, £', F, G, H). Among these five or six, two are consider- 

 ably smaller than the others, and it seems very probable that 

 these two small ones have arisen by the precocious division of 

 one of the smaller chromosomes which appears in the 12-group. 

 Whether the chromosome which divides precociously is the 

 small one of the unequal pair, is impossible to say. In fact, I 

 am inclined to think that it is not, since the irregularities in the 

 other specimens 'are not caused by this pair. 



Specimens 31-1, 31-2, and 26. The latter two show no irreg- 

 ularities in either maturation division. Since 31-1 shows only 

 one irregularity I have placed it in the same group. In this 

 specimen, 39 counts of the first division showed 12 chromosomes. 

 In the second division, 69 counts gave 12 chromosomes and one 

 13, the only irregularity observed. In 31-2, 34 counts of the 

 first division gave 12 chromosomes and 70 counts of the second 

 gave the same number. In 26, three cells of the first division 

 gave 12 chromosomes and 22 counts in the second division also 



