Spermatogenesis in Asilus notatus Wied., (Diptera). 
443 
the Hemiptera. It also resembles, as far as \ve can see, tlie early restiiig 
Stage of the spermatogoiiia. It is passed tlu’ough very rapidly and is only 
represented by a few scattered groups of cells at the border between the 
final spermatogonia and the clearly niarked region in which the next stage 
(stage b) is represented. 
The transition from stage a to stage b appears to involve merely the 
condensation of the flocculent bands into definite chroinosonies. Fig. 15 
represents tvvo nuclei in a transitional stage. Such nuclei are found adjacent 
to those of stage a, and as the figures indicate, they agree with these in 
size — no growth having taken place up to this time. The first evicTence 
of growth is found in stage b which is represented in fig. 16 to 18. Here 
the seven bivalent bodies are clearly represented. Six of them are elongate 
and granulated; the seventh is composed of two parts, a nucleolus and an 
attached chromosonie. The latter together are believed to represent the 
sex-chromosomes. 
Stage b in A. notatus is more distinct than the corresponding stage in 
A. sericeus, and involves a more pronounced contraction of the clmomo- 
somes. These become short and thick in contrast to the more threadlike 
ones of the latter species. They stand out distinctly and all seven (in- 
cluding the nucleolus) may readily be counted in hundreds of cells. Like- 
wise their bivalent structui’e is revealed more clearly than in the case of 
A. sericeus. 
Structurally stage b resembles the late resting stage of the sperniato- 
gonia, in which the chroniatin is Condensed into seven bivalent aggregates 
that give rise to the prophase chromosomes (compare figs. 5— 7 with 16 
and 17), although the bodies are more Condensed and definite in outline 
than those of the spermatogonia. Seen by themselves they would be taken 
for prophase bivalents, especially at the period of maximuni concentration 
represented by fig. 17. 
The difference between A. notatus and A. sericeus in respect to the 
condensation of the chromatin in stage b, parallels so closely the difference 
in chi'omosome behavior during the spermatogonia! resting stage and 
prophase, that one can hardly avoid the impression that in both species 
the processes leading up to stage b are essentially repetitions of those 
in the spermatogonia. 
The nuclei of stage b are readily distinguished from those of any other 
stage and form a clear cut zone across the testis just below the boundary, 
of the sperniatogonial region. Since such a large nuniber of cells are present 
all showing the same features, we have no hesitation in emphasizing this 
stage as characteristic and as marking the beginning of the growth period. 
