L. DONCASTER 13 



eggs which give clear figures, and am inclined to regard the double 

 chromosome merely as one which has begun its normal division some- 

 what in advance of the rest. 



I have good figures in the eggs of ten females of the strain with 

 55 oogonial chromosomes ; in altogether about 37 eggs both inner and 

 outer plates can be counted, and in some 20 more one or other (usually 

 the outer) can be counted. 



In all the good figures in which the chromosome number in both 

 inner and outer plates can be determined with certainty, there are 28 

 in one and 27 in the other (Figs. 11 — 13). In some families there are 

 about equal numbers of each arrangement, e.g. in brood '13.48 there 

 are two cases with 28, three with 27, in the outer plate. This family 

 is known to include males. In other ftimilies there .seems to be con- 

 siderable excess of eggs which have 27 in the inner plate and 28 in 

 the outer; e.g. in brood '13.4 B, excluding five cases in which there 

 is some doubt, there are four clear figui'es with 28 in the outer and 

 27 in the inner, nine in which either the outer can be counted as 28 

 or the inner as 27, although the second plate is not countable, and 

 only two in which the outer spindle has 27, the inner 28. In brood 

 '13.34 there are three with 28 in the outer, 27 in the inner, one with 

 27 in the inner and the outer is not countable, and one, which is too 

 oblique for quite safe determination, which appears to have 28 in the 

 inner group. In these two families, four females have been reared from 

 '13.4 B, and the surviving six larvae proved to be female by dissection, 

 and in '13.34 ten larvae were dissected, all females. There are thus 

 indications that both broods had a large excess of females, and taken 

 together they show 17 cases with the unpaired chromosome in the 

 outer plate against two or three with it in the inner. Since females 

 of this strain have 55, males 56 chromosomes, it is evident that eggs 

 with 27 in the inner spindle, and therefore in the mature egg-nucleus, 

 must be female-determining. It is thus to be expected that broods 

 which have a great excess of females should show a corresponding 

 excess of eggs with 27 chromosomes in the inner spindle. I have 

 not yet been able to find a batch of eggs in which all have 27 

 in the inner plate, and family '13.4 appears to contradict the results 

 obtained from '13.4 B and '13.34. Seven females have been hatched 

 and ten dissected in this family, and yet the eggs show a majority of 

 cases with 28 chromosomes in the inner plate (twelve with 28 in the 

 inner plate or 27 in the outer, eight cases of the converse arrangement). 

 In all three families '13.4, '13.4 B and '13.34, there was considerable 



