Spermatogenesis in Asilus notatus Wied., (Diptera). 
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essentially alike in two; yet it also involves a confiised staye (stage c) 
not nnlike the more extreme confused stage in other groups of Diptera. 
This suggests that the spinning out of the chroinosomes and the loss of 
staining capacity in the latter cases niay be merely a superficial phenoinenon 
connected with grovvth, and that synapsis and general chromosome behavior 
during the growth period may be essentially as simple as in Asilus sericeus. 
So far as known at present there is no positive evidence against this 
view, and it seems to be the niost plausible hypothesis available. In 
Dasyllis — a genus of the Asilidae, belonging to a different subfamily 
from Asilus — synapsis appears to occur before the growth period begins 
(Metz ’22), although it is not as intimate as in Asilus. In other genera of 
the Asilidae the early stages also appear to agree with these, even though 
later stages may differ widely (unpublished data). 
Summary. 
1. Spermatogenesis in Asilus notatus agrees in essential respects with 
that in Asilus sericeus described in an earlier paper (Metz and Nonidez ’21). 
2. The chroinosomes are associated in pairs as they pass to the poles 
in the final spermatogonial anaphases (as in.preceding anaphases). 
3. This association of homologues appears to become more intimate 
in telophase. 
4. After a very brief stage (stage a) in wliicli the chromatin loses 
much of its staining capacity the pah's reappear in the form of short, 
dense bivalent chromosomes (stage h). 
5. Synapsis has apparently taken place in anaphase or telophase and 
the leptotene stage has been omitted. 
6. The growth stages after stage h differ markedly from those of 
A. sericeus in superficial appearance, because the chromosomes draw out 
into long threads which become so entangled that they cannot be traced 
individually, as they can in A. sericeus. 
7. Homologues appear to remain associated during this process, 
however, as in A. sericeus, and their behavior is believed to be essentially 
the Same in the two species. 
8. A comparison of these conditions with those in other families of 
Diptera — where the chromatin is diffuse throughout much of the growth 
period — suggests that A. notatus may represent a condition interniediate 
between that in A. sericeus and that in many other Diptera, and that it 
may be possible to bring all types within a common general scheine in which 
synapsis occurs in the anaphase or telophase of the final spermatogonial 
division. 
