Spermatogeiiesis in Asilus iiotatus Wied., (Diptera). -idl 
The proccss of condensatioii is not uniform at fh’st, and as the ag- 
gregates appear they are iiTogular in outline, certain regions being much 
denser and thicker than otliers. Thus one aggregate is frequently composed 
of two or inore heavy portions connected by thin Strands (fig. 5). At such 
stages it is possible to coimt ten or twelve niasses in the nucleus, but as 
condensation progresses the mmiber is reduced to froni six to eight, usually 
seven — corresponding to the seven pairs of chromosonies. 
The latter condition is represented in fig. 6, an entire, or practically 
entire nucleus. In the figure the spatial Separation of the different ag- 
gregates is not so clear as it appears under the microscope, because the 
long aggregate (2) in the center of the figure lies above two of the short 
ones. The latter are represented in lighter shade to indicate their position 
at a lower level. One of them — lettered n in the figure — is the nucleolus 
attached to a small chromatic aggregate. The other six are indicated by 
numbers 1—6. Kumber 5 appears to be comprised of two portions iniper- 
fectly United, and in nuniber 2, as may be seen, condensation is not yet 
complete, although the parts are plainly connected. In prophase each 
aggregate gives rise to a long double thread by a process of attenuation or 
uncoiling (figs. 7—9). This thread shortens up ininiediately into a pair 
of prophase chromosonies. 
The only apparent difference between this species and A. sericeus, in 
spermatogonial behavior, is the earlier condensation of the chromatin 
into chromosonies in prophase. This is noted especially because it seenis 
to be reflected by a siniilar difference in the first sperniatocytes. 
The final spermatogonial telophase is iiiore difficult to analyse in 
Asilus notatus than in A. sericeus, partly because of its larger nuniber of 
chromosonies. So far as we can deterniine, however, the processes occiir- 
ring here are alike in the two species. In anaphase the chromosonies are 
associated in pairs as they go to the poles (fig. 11). Then the pairing appears 
to beconie iiiore and niore intimate (fig. 12), until the two homologoiis 
elenients become United (fig. 13). 
IVe have described the process in Asilus sericeus as follows (’21, p. 169j: 
‘‘In late anaphase the pairing becomes more intimate, due partly to the crowding 
of the cliromosomes at the poles. Then in telophase the crowding is relaxed, the duster 
loosens up, and the individual cliromosomes may be observed. They are now intimately 
associated in pairs — so intimately, indeed, that the duality is often obscured. ln other 
words, as the duster loosens, the chromosonies separate out as bivalents instead of single 
dements. In figs. 6 and 7 different degrees of association are represented. Some of the 
chromosomes sliow the dual structure clearly, while otliers show it very little or not at 
all. These nuclei are entire, or nearly so, and all of the chroniatin is represented. Fig. 8 
