B. F. Kingsbury 117 



shows a stage slightly older than that illustrated iu Fig. 19. A careful 

 count at this time reveals twelve of these groups of double chromosomes. 

 Polar views of the nucleus of the spermatocyte of the second order are 

 shown in Figs. 20 and 21, while Fig. 22 represents a deep (equatorial) 

 section through a nucleus, showing the chromatin threads cut across. 

 The chromatin threads are at first long, fine, and irregular in thickness, 

 and rough in outline, though a regular succession of chromatin granules, 

 such as made up the chromosomes of the growing spermatocyte of the 

 first order, is not so evident. The linin is at first scanty in amount 

 but increases as the nucleus gi'ows, though it never becomes relatively as 

 abundant as in the spermatocyte of the first order. It forms a coarse 

 mesh-work between the chromosome threads, attaching to them, and 

 thus giving them their irregular outline. The question of the source of 

 the linin of the spermatocyte of the second order is one to which no 

 attention has been given in this investigation, though it is of consid- 

 erable interest. 



The chromosomes shorten and thicken corespondingly, thereby losing 

 their rough outline. The groups of four chromatin threads are in this 

 way converted into crosses or X's, which tend to lie superficially under 

 the nuclear membrane, Figs. 23-27, as did the chromatin rings in the 

 spermatocyte of the first order, and so lose their original polar orienta- 

 tion. At about the time of the dissolution of the nuclear membrane, 

 the X's separate into their component V's which become involved in the 

 spindle. Fig. 29. Their distribution at the time they are first formed 

 is apparently without order or system, so that the equatorial plate stage 

 is one of loose formation. Typically, when the cross is dissolved, the 

 two component V's become applied to each other, and thus are drawn 

 into the equatorial plate in pairs, Fig. 29. This, however, does not 

 seem to be always the case, so that often the V's are separated from each 

 other and promiscuously scattered. 



The remaining stages in the mitosis of the spermatocyte of the second 

 order have been well described hj other workers, Flemming, Meves, 

 McGregor, and need not be repeated here. The equatorial plate, ana- 

 phase and telophase are shown in Figs. 30, 31 and 32, and from them 

 one may see that the processes are essentially identical with those de- 

 scribed long ago by Flemming in Salamandra. The chromosomes be- 

 come closely massed as they pass to the pole, as was the case in the 

 spermatocyte of the first order. Fig. 32. They become separated again 

 in the dispirem stage, and are once more apparent as V's, twelve in 

 number, with their apices toAvard the pole of the cell. Fig. 33. These 

 soon lose their form and oive rise to a fine reticulum characteristic of 



