250 WILBUR WILLIS SWINGLE 
the so-called 'resting' period, preparatory to undergoing the com- 
plex phenomena of maturation. As stated before, the nuclei of 
the primary and secondary spermatogonia soon become poly- 
morphic in character, following division, and the chromatin mate- 
rial is found scattered throughout the nucleus in bead-like masses 
or granules, attached to an irregular linin network. In sharp 
contrast to this type of nuclear reconstruction, nuclei of the last 
spermatogonial telophase are round or oval in shape and of small 
size. The chromatin is in the form of small lumps or blocks 
(Janssens, '03) somewhat irregular in outline. In especially fav- 
orable cells the number of these blocks can be made out with a 
fair degree of accuracy. Their number is certainly diploid. The 
writer is inclined to regard these chromatin blocks as representing 
individual chromosomes at this stage. In early stages they are 
independent of one another, but very soon anastomosing linin 
fibrils appear between them. 
The preleptotene period (Gregoire, '07) marks the first indica- 
tions of resolution of the blocks. They become woolly or mossy 
in appearance, delicate, much coiled, and tangled thread-like 
processes appear, as if spinning out from the chromatin material 
in the mass. During the course of these changes the nucleus 
increases in size (figs. 8 and 47). These tangled threads so 
characteristic of the preleptotene elongate, lose their spiral-like 
character, and extend across the nucleus in loops. At this period 
there is no definite orientation of the leptotene filaments. Appar- 
ently, for the writer cannot speak with certainty on this point, 
each of the chromatin blocks of the telophase nuclei gives origin 
to a single thread. It is difficult, if not impossible, to unravel 
the snarl of elongating threads crowding the nucleus at the time 
of their first appearance. Wenrich ('16) has been able to trace 
the origin of the leptotene threads with cdnsiderable clearness in 
Phrynotettix magnus, and he is of the opinion that a single 
chromatin block gives rise to a single filament. This view seems 
very probable, when consideration is taken of the fact that the 
number of leptotene filaments is diploid and corresponds closely, 
if not exactly, to the number of blocks. Judging from Wenrich's 
figures, conditions in Phrynotettix at this period are much more 
favorable for study than in Rana catesbeiana tadpoles. 
