4.72 Chromosomes of Anasa Tristis and Anax Junius 
Our re-examination of Anax, therefore, brings this dragon-fly into com- 
plete accord with those insects, like Anasa and Protenor, in which an odd 
number of chromosomes is found in the spermatogonia and an asymmet- 
rical distribution of the heterotropic chromosome takes place at one of 
the maturation divisions, resulting in a dimorphism of the spermatids. 
These observations consequently lend additional support to Wilson’s 
interpretation of the relation of the chromosomes to sex-production. 
In the following account, the general course of spermatogenesis in 
Anax will not be traced, as this will be found in Miss McGill’s original 
paper, but only such points will be brought out as require correction or 
further amplification. 
THE SPERMATOGONIAL GROUP OF CHROMOsoMES.—As already stated, 
the number of chromosomes is 27. This has been determined with per- 
fect clearness in a very large number of cases and has been found to hold 
true without exception. Whenever the equatorial plate is cut transversely 
at full metaphase, the chromosomes are seen lying well apart and sharply 
defined, while the counting of their number is a matter of the greatest 
ease. It is only in unfavorable cases, as in insufficiently extracted sec- 
tions or through a close crowding of the chromosomes, that an accurate 
count is rendered uncertain. In properly stained sections, an unlimited 
number of cells have been found which show 27 distinct chromosomes, 
never more. 
The size differences in the chromosomes are well marked, although not 
so strikingly as in many of the Hemiptera. Between the m-chromosomes, 
which are the smallest pair, and the largest pair or macro-chromosomes, 
which are usually quite perceptibly larger than any of the others, the 
remaining chromosomes, except the odd one, may be arranged in pairs of 
intermediate sizes. The differences among the latter, however, are only 
slight and some pairs are of approximately equal size (Fig. 2, A and B). 
After pairing off all the others, one will be left without a mate, and this 
will be found among those of intermediate size. The exact chromosome 
cannot be identified as the odd one, as the sizes are not sufficiently dif- 
ferentiated to allow of an accurate pairing of all the remaining chromo- 
somes, and furthermore some of the chromosomes exhibit a certain irreg- 
ularity of form which increases the difficulty. 
In side views, the spermatogonial spindles show a flat equatorial plate 
at metaphase, with all of the chromosomes lying in the same plane (Fig. 
2, C), and here, as in Anasa, polar views at this stage exhibit without 
doubt the full number of chromosomes. 
The spermatogonial divisions have been adequately described by Miss 
