CHROMOSOMES OF PERLA 511 
chromosome group consists of two pairs of V’s, a pair of rods, 
two spherules (m-chromosomes), and two unpaired rods, one 
of which is much longer than the other. These last I interpret 
as X- and Y-chromosomes, respectively. 
Figures 3 to 5 show the changes in the nucleus subsequent 
to the last spermatogonial division. The nucleus in the late 
anaphase of the division (fig. 3) gradually enters into the resting 
stage (figs. 4 and 5), when the reticular appearance of the nucleus 
is resumed. 
The chromatin reticulum then begins to form the double 
spireme. The process of the formation of the double spireme 
is illustrated in figures 6 to 13, and may be best described as a 
development of dual threads out of the reticulum. There is 
no sign of two threads coming to conjugate side by side. It 
is also impossible to say that the process involves the .actual 
splitting of a simple thread. As may be seen very clearly, there 
are no definitely formed and separate simple threads (i.e., 
chromosomes) in the nucleus before the development of the 
double spireme commences. 
The stage of contraction seems to follow the completion of 
double threads. This seems to correspond to the period of 
synizesis of some authors. The nuclei in this condition are 
shown in figures 14 and 15, and it will be readily seen that the 
contraction has nothing to do with the formation of the double 
threads. The spireme at this stage is unquestionably already 
double in structure. More or less regularly accompanying the 
contraction nuclei, there are a number of nuclei in the process 
of degeneration. Four degenerative cells are shown in figures 
16 to 18. 
The duality of the spireme (zygotene thread) seems to be 
maintained all through the later stages (figs. 19 to 23). 
The actual number of the prochromosomes could be counted 
at the pachytene stage (figs. 24 to 26), when the nuclei enlarge 
a little, and the spireme threads become more compact. As 
can be seen in figures 24 to 34, there are six separate segments 
recognizable at this stage. The smallest one, which is sometimes 
attached to the largest (fig. 32), will be seen to represent the 
