SPERMATOGENESIS IN ASILUS SERICEUS 175 
The polarized stage persists almost up to the first spermatocyte 
prophase, and is modified, toward the end, by a definite contrac- 
tion period (fig. 17) in which the threads draw away from the 
nuclear wall and lie close together. Apparently no significance 
attaches to this contraction for the threads undergo no visible 
changes and soon spread out again into their previous positions 
near the periphery (figs. 20 and 21) and condense into the five 
prophase chromosomes, ready to go on the spindle. 
Although these processes cover about four-fifths or more of 
the growth period and are represented by many thousands of 
cells, they are so simple and involve such slight changes in the 
chromatin, that in essentials the condition found in stage b 
(fig. 13) may be said to typify all the succeeding stages up to 
the prophase, and the whole series may be represented by a few 
figures. The diplotene threads that appeared at the beginning 
of stage b have persisted unchanged so far as their diplotene 
structure is concerned. The contraction stage, occurring in the 
late growth period, if it has any counterpart, outside of the 
Diptera, would represent the so-called second contraction, taking 
place long after synapsis. 
These events seem to resemble those in Thalictrum (Overton, 
'09) to the extent that the chromatin remains in the form of 
relatively condensed, bivalent threads. Compared with animals, 
however (other than Diptera), there is no such resemblance, for, 
as just mentioned, the leptotene and synaptic stages usually 
following stage b are not found in Asilus. 
THE SPERMATOCYTE DIVISIONS 
Since this paper is concerned primarily with the growth stages, 
the maturation divisions will be passed over briefly. So far 
as known, they present no unusual features. Metaphases of 
both spermatocyte divisions are clear, and each shows five 
chromosomes. Only the first is represented here (fig. 22). It 
is the reduction division, apparently, for no tetrad structure is 
evident. 
