440 
Chas. W. ]\Ietz and Jose F. Xonidez 
narrow' transition zone (text fig. 1 1) in which spermatogonial anaphases 
and telophases are intermingled with tlie earliest stagcs of tlie first sper- 
niatocytes. The niiclei lierc are very small. Following this, is another 
Zone, narrow bnt clearly defined, containing cells nearly all of which are 
in one stage (text fig. 1 h). Froin this point the development involves 
a gradnal transformation which may be followed with comparative ease 
through the long growth period extending far down the testis. In favorablo 
material all of these stages appear in one preparation, or even in onc 
section, and since there is such a large number of cells available for study, 
even the intermediate transition stages, often so difficult to obtain, are 
nearly all in serial Order. The only exceptions to this rule are found in 
the stages immediately following the last spermatogonial anaphases. Here 
development proceeds with great rapidity, and the telophase and associated 
stages are inore or less intermingled. Bnt in spite of this it is possible to 
obtain a clear conception of what takes place, for the immediately suc- 
ceeding stage (b) is perfectly clear and with its aid the other figiu’es may 
be pieced together. The details of these processes will be given below. 
Spermatogonia. 
The spermatogonia are numerous and easily studied in our material. 
As in Ä. sericeus those of the last generation or two are noticeably smaller 
than the others and their chromosomes are more closely aggregated during 
metaphase. bnt otherwise they appear to be essentially like the rest. The 
main pecularities of chromosome behavior in spermatogonia and other diploid 
cells of flies have been described in an earlier paper (Metz ’16), and may 
l)e passed over briefly here. It should be recalled, however, that the dose 
association of homologons chromosomes, especially during prophasc, makes 
the pairs of chromosomes simnlate the single chromosomes of other animals. 
In spermatogonial metaphases of A. notafus there are f ourteen chromo- 
somes, arranged in seven pairs, the smallest of which is the sex-chronio- 
some pair (figs. 2, 3, 10). Occasionally the arrangement of one or two 
pairs is disturbed, bnt normally they all show the paired association just 
as in other Diptera (Metz ’16). In anaphase the chromosomes pass to 
the poles in this paired condition (fig. 11), and in telophase they become 
diffuse and pass into the resting stage as shown in fig. 4. It does not seem 
probable that a true network is formed at this stage, for shortly afterward 
the chromatin reappears in irregulär aggregates (fig. 5—7). This con- 
densation apparently occurs very early, for most of the resting nuclei 
show the chromatin collected into aggregates, which later give rise to the 
seven chromosome pairs. 
