172 CHARLES W. METZ AND JOSE F. NONIDEZ 
peculiarity of the dipteran chromosomes — their characteristically 
paired association in somatic cells. 
It is of interest to consider the events up to this point in relation 
to those found in other insects, such, for instance, as the Hem- 
iptera, Odonata, and Orthoptera. A marked similarity is at 
once noticeable in many features, but always with the difference 
that the chromatic elements of Asilus are double instead of single. 
Thus in Oncopeltus Wilson ('12) describes the stages immedi- 
ately following the final spermatogonial divisions as involving 
a diffusion of the chromatin in telophase followed by a stage in 
which definite prochromosome-like aggregates arise (compare 
Wilson's figures 48 to 51 with our figures 9 to 13.)^ These aggre- 
gates or masses would correspond to those of stage b in Asilus, 
but instead of being haploid in number and bivalent in compo- 
sition, they are, in Oncopeltus, diploid in number and apparently 
univalent in composition. 
In Lygaeus among the Hemiptera (Wilson, '12), Anax among 
the Odonata (Wilson, '12), Phrynotettix, Dissosteira, and 
Chortophaga among the Orthoptera (Davis, '08; McClung, '02; 
Wilson, '12), and probably in numerous other forms, phenomena 
not essentially different from those in Oncopeltus are found, so 
that the comparison of Asilus with Oncopeltus may be extended 
to include several species representing a widespread type of 
spermatogenesis as regards the earliest stages of the growth 
period. 
Apparently the Coleoptera may also be put in this class, 
although there are so many conflicting accounts of coleopteran 
spermatogenesis that many cases are open to question. The 
essential features, however, namely, the resting stage followed 
by the appearance of more or less condensed masses or aggregates 
in diploid number, seem to be well established in certain instances 
(Stevens, '05, '06, '08 a, '09; Nonidez, '14, '15; Goldsmith, '19, 
figs. 17, 18, 19). 
^ This resemblance is even more strikingly shown by another species of Asilus 
(A. notatus) in which the prochromosome-like bivalents are more condensed and 
shorter than in A. sericeus (discussion, page 178). 
