THE SI'EKMATtXiENESIS OF IKJMESTIC MAMMALS. 215 



iittiiclimeut of tlio spiudle fil;er Ls terniiiinl, nltLoiigh iis iu the mouse tlio 

 ixjiiit of atbichmeiit cim not be seen (Figs. 92, 94). 



In the resting spermiitogoDia the itliozome can cleai"ly be seen as a long 

 ellipsoid and is sitimte<l constantly in close contact to the nuclear wall 

 (Fig. 145). 



The niitochondi'Lal granules appear abundantly in the cytoplasm. Their 

 sizo and their behavior are entirely the sjvme as those of the m.juse (Fig. 

 93). 



II. The Growth Period of the Spermatocyte. 

 A. The growth period of the spermatocyte in tlie mouse. 



In tlie final telophase of the spermatogonia the chromosomes break up 

 into a coufusetl cet-like structure, and for a short time the outline of the 

 individiuil chromosome can not be distinguished (Fig. 129). Soon after many 

 chromatin masses appear, connected with fine threads (Fig. 15). The number 

 of the chromatin masses is almost equal to that of the spermatogonia! 

 chromosomes. 



The pre-synaptic stage : — At the beginning of this stage the irregular 

 chromatin masses which appeared in the previous stage begin to elongate 

 and finally become the chromatin threads which are comparable to those of 

 cattle, but they are very short and appear as in-egular chromatin rods (Fig. 

 16). Even though the niunber of the chromatin threads can not be exactly 

 coimtcd in this stage, it is clearly sho'v\n that theii" niunber is not far from 

 that of the spermatogonia! chromosomes (Fig. 16). In the preparations 

 stained with Auerbach's method, all the chi'omatin threads are stained 

 intensely with methyl-gi-eeu, and no nucleolus is foimd in any part of the 

 nucleus (Figs. 129, 130). 



In this stage the mitochondrial gninules ajjpeai" in small uimiber in the 

 cytoplasm (Fig. 16;. 



The synaptic stage : — After the brief duration of the pre-synaptic stago 

 the chi'omatin thi'eads soon begin to converge towai-ds one side of the nucleus, 

 leaving a clear space on the other side (Figs. 17, 130). But the tendency 

 of the polarization of the chi'omatin threads is not so conspicuous as that 



