Spermatogenesis in Asilus notatus Wied., (Diptera). 
Von 
Clias. AV. Metz and Josd F. Nonidez, 
Department of Genetics, Carnegie Institution of AVashington. 
Mit 1 Textfigur und Tafel XXI— XXIII. 
The present study is iiiteuded to Supplement our earlier one on Asilus 
sericeus (Metz and Xoxidez ’21), and is of interest primarily in Con- 
nection with that study. It serves to illustrate the constancy of certain 
phenomena found in A. sericeus, and at the same time it appears to re- 
present a condition somewhat intermediate between that found in sericeus 
and those found niore commonly in other families of Diptera. 
Aside front its possible bearing on genetics, the study of gametogenesis 
in the Diptera is of interest front the ptirely cytological standpoint becatise 
the cltromosome behavior, both in somatic cells and dtu'ing gametogenesis, 
(or spermatogenesis at least) appears to diverge widely from that found in 
most other orgattisms. A detailed discussiott of general features has beett 
givett in our earlier paper (1. c.) and will be omitted here. 
ln sottte respects Asilus notatus provides the most favorable material 
for the study of spermatogenesis thus far secttred antong the Diptera. 
The early growth stages of the primary spermatocyte, which are perhaps 
of greatest interest for present pitrposes, are represented in an ttnusually 
clear-cut fashion. In addition this species agrees with Asilus sericeus and 
many other asilids in having the successive stages of spermatogenesis 
represented in serial order down the long, tubulär testis, and in providing 
in one specimen all stages from spermatogonia to spermatozoa. This 
simplifies the matter of orienting the stages and practically eliminates 
the danger of omitting any significant stage from the account. 
Asilus sericeus was used in the previous account because of the sim- 
plicity of the processes occurring during the growTh stages — due in part 
to the absence of any “confused” stage in which the chromosomes could 
not be seen individnally. In this respect the present species differs from 
A. sericeus and niore nearly approaches the condition found more generally 
among the Diptera. As will be indicated below, however, it is believed 
