166 CHARLES \V. METZ AND JOSE F. NONIDEZ 
These considerations led the senior author some time ago to 
begin gathering material for a study of gametogenesis, in con- 
nection with other studies on Diptera chromosomes, and the 
first results of this study are presented here. From the genetical 
standpoint the present paper represents only a short step in the 
desired direction, but it may serve as a foundation upon which 
to base further work — particularly studies on oogenesis, which 
are under way at the present time. 
Two reviews of the literature on Diptera chromosomes have 
been given recently (Metz, '16, pp. 213, 214; Whiting, '17). 
From these it will be seen that most of the work on the subject 
has dealt primarily with the sex chromosomes or other special 
features, and that our knowledge of gametogenesis, especially 
the growth stages, is meager. 
In her studies on the sex chromosomes, Stevens ('07, '08, '10, 
'11) records several observations on other aspects of spermato- 
genesis, but unfortunately these cannot be combined to make a 
connected account. The observations of Taylor ('14) and of Lomen 
('14) on Culex, in addition to being meager as regards details of 
spermatogenesis, are, we believe (see also Whiting, '17), faulty 
on account of the poorly fixed material used. Whiting ('17), in 
a more recent paper on Culex, has given a comprehensive account 
of the maturation divisions, beginning with the first spermato- 
cyte prophase. His observations on the earlier stages, however, 
particularly the earlier part of the growth period, are limited, 
probably owing to the fact that Culex does not afford favorable 
material for this purpose. 
As regards oogenesis in the Diptera, practically nothing has 
been published, so far as we are aware. 
Unfortunately, the Diptera have long, and justly, been looked 
upon as unfavorable objects for cytological study — a fact that 
has undoubtedly been responsible for keeping our knowledge of 
gametogenesis in this group far behind that of such insects as 
the Orthoptera, Hemiptera, and Coleoptera. We have found, 
however, that some groups of Diptera are much more amenable 
to study than others, and by making selections from these and 
by careful attention to technique we have been able to obtain 
