174 CHARLES W. METZ AND JOSE F. NONIDEZ 
I have attempted to trace the processes of reconstruction of the 
nucleus of the pollen mother-cells from the last pre-meiotic division, 
and to compare the structure of these nuclei with that of ordinary 
somatic ones, but have experienced considerable difficulty in identify- 
ing with certainty the last pre-meiotic divisions. After the formation 
of the nuclear membrane and during the period of nuclear enlargement, 
the chromatic material becomes rather regularly distributed in the 
nuclear cavity, the greater portion of the stainable substances lying in 
the prochromosomes, each suggesting by its form and size that it is 
derived from a chromosome of the preceding telophases. I am not 
prepared to discuss the problem as to how the chromosomes of the 
telophases are modified in passing over into the resting nucleus. 
(Overton, '09, pp., 21, 22.) 
In Oncopeltus and the other insects mentioned above, the 
prochromosome-like bodies of stage h, whether massive (Wilson's 
stage b in Hemiptera and Anax) or more thread-like (Davis's 
stage b in Orthoptera), give rise, by a process of unraveling, to 
long, delicate leptotene threads that then undergo synapsis to 
form the pachytene or diplotene threads. Since, in Asilus, the 
chromosomes are already double (i.e., bivalent) it is of especial 
interest to examine their subsequent behavior. 
LATER GROWTH PERIOD 
The transition from stage b to later stages involves merely a 
gradual lengthening out of the five diplotene threads (figs. 13 
to 16) and their polarization with reference to the nucleolus. 
One member (apparently the smallest) is already attached to the 
nucleolus. The others, or at least two or three of them, soon 
become attached and extend out like fingers (figs. 16 to 20). 
Apparently each thread becomes attached at one end only. No 
cases have been found in which a complete loop was formed. 
Fortunately, the threads lie close to the nuclear wall and remain 
\vell separated from one another throughout almost the entire 
growth period, so they may be examined readily. They show 
no indication of dissociation into single (leptotene) threads at 
any stage, although their duality is evident throughout. As 
may be noted from the figures, the nucleus decreases somewhat 
in size instead of enlarging as polarization progresses. 
