‘George Lefevre and Caroline McGill 473 
McGill, and the details need not be repeated here. All of the chromo- 
somes divide longitudinally and pass in similar daughter groups to the 
poles, while after the last division the young spermatocytes. enter upon 
the growth period. 
THE FEMALE Somatic CHroMosoMEs.—An attempt has been made 
to determine the number of chromosomes in the female germ-cells, and 
sections of the ovaries of the nymphs have been carefully examined. 
Although no odgonial divisions have been encountered, possibly because 
we have not been able to obtain ovaries from young enough nymphs, 
nevertheless mitosis occurs abundantly among the follicle cells and a 
detailed search has disclosed several cases where the sections were favor- 
able for counting the chromosomes. It might be remarked that Miss 
McGill, 06, in her study of the ovarian history of the germ-cells in the 
same dragon-fly has shown that the follicle cells have the same origin as 
the odgonia, both being differentiated from cells of the end-filaments of 
the egg-strings, and there is, therefore, every reason for supposing that 
their chromosomes are essentially the same. The number of chromo- 
somes in the follicle cells has been determined in several instances, and 
wherever an accurate count has been possible, it has been found to be 28. 
Two of these cases are drawn in Fig. 2, D and £#, and show the full 
number distinctly. The size differences are not as well marked as in the 
male groups, although the m-chromosomes are readily identified in D, 
and a decidedly largest pair is seen in H. The chromosomes, however, 
appear somewhat smaller and show a slightly greater irregularity of form 
than do those of the male group. This is especially true of D, the group 
E being more nearly like the male in the size and shape of the chromo- 
somes. In both of these cases, and also in a few others where an accurate 
count has been possible, the chromosomes had not quite come to full 
metaphase. They had, therefore, not reached their complete condensation 
and were evidently not lying in their final orientation on the spindle, 
with the result that they appeared in the sections at varying angles. This 
fact explains their irregularity of form, and, doubtless, a longer search 
would have revealed more favorable cases showing a closer similarity to 
the size and shape of the male chromosomes. Still, the cases illustrated 
exhibit a striking correspondence, and it is a matter of great importance 
for the theory of sex-chromosomes to know that the female number is 28, 
while that of the male is 27. It is, furthermore, of interest to find that 
the same differences among the chromosomes exist in a member of the 
Odonata as have been shown to occur in the Hemiptera and other groups 
of insects. 
