George Lefevre and Caroline McGill 471 
when the two groups can be observed in the same cell, they furnish an 
absolute demonstration of the inequality of the distribution of the 
chromosomes at this division, with the result that the heterotropic chro- 
mosome passes into one of the spermatids and not into the other. 
The evidence presented by a study of the chromosomes of Anasa tristis, 
obtained in a locality widely separated from the places where other 
observers who have examined this form have secured their material, would 
seem to indicate that Wilson’s description, especially with regard to the 
behavior of the heterotropic chromosome, holds good throughout the 
species. 
In view of the important bearing which these facts have upon the 
chromosome-theory of sex-determination, it has seemed advisable to add 
a confirmatory note to the already clear and convincing observations of 
Wilson on this and other hemipterans. 
ANAX JUNIUS. 
The spermatogenesis of this dragon-fly was first described in 1904 
by Miss McGill, 04, who found a close similarity to Paulmier’s 
account of Anasa tristis. Like him, she described an even number 
of spermatogonial chromosomes, in this case 28, and followed him in 
identifying the accessory chromosome of the maturation divisions with 
the two small chromosomes of the spermatogonia which were supposed 
to have united to form a bivalent at synapsis. The accessory chromosome 
was correctly observed to divide at the first maturation mitosis and to 
pass undivided to one pole at the second, as Paulmier had described for 
the squash-bug. 
A recent study, however, of the testis of Anax has brought to light the 
fact that the same error was made as in the case ofAnasa, since it has 
been determined beyond any doubt that the number of spermatogonial 
chromosomes is 27 and not 28. It is, furthermore, clear that the small 
or m-chromosomes of the spermatogonium divide at both maturation 
mitoses, and hence cannot be identified with the accessory which is one 
of the larger chromosomes, though not the largest of the spermatogonial 
group. Miss McGill was also unable to find evidence in the material 
which she examined of a condensed chromosome-like body persisting 
throughout the growth-period, but in our more recent study this has 
been clearly demonstrated at every stage of the resting spermatocyte unti! 
it passes on the spindle of the first maturation mitosis. Judging from 
its size-relations and other considerations, it is unquestionably the odd or 
heterotropic chromosome. 
