THE CHROMOSOMES OF ANASA TRISTIS 
AND ANAX JUNIUS. 
BY 
GEORGE LEFEVRE anp CAROLINE McGILL. 
From the Zoological Laboratory of the University of Missouri. 
WITH 5 FIGURES. 
ANASA TRISTIS. 
The material for the study of the chromosomes in the spermatogenesis 
of Anasa tristis was obtained at Columbia, Mo., and was examined by 
means of sections. A careful investigation has completely confirmed 
Wilson’s results, 05, 06, 07, respecting the number of spermatogonial 
chromosomes in this insect and the presence of an accessory or hetero- 
tropic chromosome, as well as the asymmetrical distribution of this 
chromosome, at the second maturation division. The observations here 
presented are, on the other hand, at absolute variance in all important 
points with the recently published investigation of Miss Foot and Miss 
Strobell, 07, who have studied and photographed smear-preparations of 
the testis of Anasa tristis. 
Wherever an accurate count of the spermatogonial chromosomes can 
be made at full metaphase, the number has been found to be 21, as dis- 
covered by Wilson, and not 22, as originally determined by Paulmier, 
99, and recently confirmed by Foot and Strobell. No exception to this 
result has been encountered, although the count has been made with cer- 
tainty in scores of cells, and not a single case showing 22 chromosomes 
has ever been observed. Many of the spermatogonial groups have been 
drawn under high power, six of which are reproduced in Fig. 1, A-/’, and 
in every instance both the number and form of the chromosomes are seen 
with diagrammatic distinctness, conforming in all respects with the 
groups as figured by Wilson. The two m-chromosomes and the three 
large ones appear in all, while one of the latter is usually bent upon itself, 
sometimes nearly at right angles, as in Fig. 1, FY. It is not at all improb- 
able that in smear-preparations this chromosome might be pulled apart 
at the angle, and thus account for the observations of Miss Foot and 
Miss Strobell. This explanation, moreover, is in a sense justified by 
their photographs of the spermatogonial groups, especially photos. 47 
AMERICAN JOURNAL OF ANATOMY.—VOL. VII. 
