206 A. W. GREENWOOD 



of the resting cell occurs in the form of rather faintly stained 

 blocks connected by fine strands. The blocks of chromatin 

 appear as loose masses, frayed out at the edges, and the number 

 present is approximately the same as the diploid number of 

 chromosomes. 



The onset of the prophase is marked by an increase in the 

 staining capacity of the chromatin blocks w^ich now give rise 

 to short irregular threads. These threads increase in length, 

 probably at the expense of the nucleolus, which now shows up 

 as a large pale body with a few deeply staining granules 

 embedded in it. The long irregular threads begin to contract, 

 ultimately giving rise to the thick chromosomes marking the 

 end of the prophase. The nucleolus has given rise to a large, 

 oval, faintly stained body, a typical plasmosome. 



Meiotic Phase. 



The origin of the leptotene stage has not been determined 

 with absolute certainty, but it appears that the telophase of 

 the last spermatogonial division does not pass into a complete 

 resting stage, but the chromatin remains in the form of blocks 

 situated close underneath the nuclear membrane. These blocks 

 are present in approximately the diploid number. They are 

 more compact and stain more deeply than the chromatin 

 blocks seen in the resting spermatogonial nucleus. The 

 leptotene stage appears to be derived from this by the formation 

 of long threads from these chromatin blocks. The early lepto- 

 tene nucleus consists of a tangle of fine threads. On the 

 threads chromomeres can be seen. These are spaced rather far 

 apart and vary considerably in size. In the centre of the 

 nucleus the pale plasmosome can be seen. Following this stage 

 the threads begin to contract away from one side of the nucleus, 

 and, at the same time, begin to contract in length. This is 

 the earliest indication of synizesis (PI. 15, fig. 4). Although the 

 exact time of syndesis could not be determined, it is probable 

 that it begins to take place now. 



It is significant that the leptotene nucleus entering synizesis 

 shows that the threads contract away from that side of the 



