Spermatogenesis in Asilus notatus Wied., (Diptera). 
44.5 
fnrthcr spinning out it is possil)le that loops inay be foniied. xMthough 
supcrficially this spinning out process seenis very different froin the 
behavior in Ä. sericeus there seems to be no question that the threads 
here remain in a paired association just as they do in the latter species. 
In some nuclei the association is not unifornily close, as e. g. in the case of 
one or niore pairs in figs. 18 to 20, but evcn though the association niay 
become loose, with open spaces (loops) appearing here and there between 
the parallel threads, the two elements of a pair do not become greatly 
dissociated. 
It wöuld appear that in the case of A. notatus the prochromosomelike 
bodies of stage h spin out much as do the somewhat similar prochromosome 
like bodies in such forms as Oncopeltus, Anax etc. (Wilson ’12, see also 
p. 174 of our previous paper) but that whereas, in the latter we find single 
or leptotene threads derived froni univalent bodies, in Asilus we have 
double or diplotene threads derived from bivalent bodies. 
The canopy-like structure of stage c persists for a short time and is 
followed by a stage in whieh the threads become more Condensed, more 
contracted, and more definitely polarized (fig. 25). Then they spread out 
again, in the form of long bivalent chromosomes (fig. 26), and henceforth 
they may be followed with comparative ease through succeeding stages 
up to the prophase (figs, 26—30). 
The development up to the end of stage c (fig. 24) has occupied ap- 
proximately half of the growth period; both cells and nuclei are now 
considerably larger than those in stage h. Düring the remainder of the 
growth period steady and fairly rapid growth continues; nuclear changes 
are slow and gradual ; the polarization disappcars, the chromatin becomes 
more and more Condensed and soon the chromosomes may be traced 
easily and counted accurately (figs. 27 and 28). There are seven bodies, 
corresponding to those of stage h. The duality of these may be detected 
at this time and throughout most of the remaining growth period, in 
properly stained sections. 
The nucleolus persists throughout stage c and nearly to the end of 
the growth period, gradually diminishing as the prophase approaches, 
until only the small bivalent chroniosome remains (figs. 28 und 29). No 
attempt has been made to determine the relations between the achromatic 
and chromatic portions of the nucleolus in the earlier stages, since the 
structiu’e is much less easily analysed than that in A. sericeus. There seems 
to be little doubt, however, that the pair of chromosomes involved is 
the XY pair. 
