SPERMATOGENESIS IN ASILUS SERICEUS 179 
The most noticeable difference between sericeus and notatus, 
however, appears in the stage immediately following stage b. 
At this time the bivalents in A. notatus, instead of lengthening 
only slightly and remaining well separated from one another, as 
they do in sericeus, become greatly attenuated and entangled 
for a time, making analysis very difficult. Here again the super- 
ficial resemblance to phenomena in the Hemiptera is more marked 
than in sericeus, although the actual structural characteristics 
(persistence of the diplotene condition) appear to agree with 
those of sericeus. 
When an attempt is made to compare spermatogenesis in 
Asilus with that in other genera of flies, confusion enters at 
once. Other members of the Asilidae show definite resemblances, 
but outside of the family superficial differences are so great that 
comparisons cannot be made safely without very careful study. 
As a case in point we may mention the genus Drosophila. Super- 
ficially spermatogenesis in this group is exceedingly different in 
appearance from that in Asilus. Further study and possibly 
detailed examination of intermediate forms will be necessary 
before the relationships can be determined. Perhaps much of 
the apparent divergence between Drosophila and Asilus is due 
to difference in the cytoplasm, rate of growth of the spermato- 
cytes, degree of staining of the different nuclear elements, and 
other secondary features, but there is as j^et no certainty that 
it may not also include fundamental differences in the chromo- 
somal behavior. 
SmiMARY 
1. The spermatogonial chromosomes of A. sericeus are ten 
in number, arranged in five pairs. The sex chromosomes have 
not been identified. 
2. In the last spermatogonial anaphase, as in preceding ana- 
phases, the chromosomes go to the poles associated in pairs. 
3. The paired association becomes more intimate in telophase, 
giving rise to bivalent chromosomes in haploid number. 
4. A brief diffuse stage (stage a) ensues, in which the chromatin 
stains only slightly. 
