130 ETHEL NICHOLSON BROWNE 



the other 13 chromosomes are to be found, including the second 

 small one, just within the peripheral ring. 



In the anaphases, the components of the small central chro- 

 mosome always lead in the procession toward the poles. The 

 second small chromosome from within the peripheral ring is to 

 be found directly behind the smallest one (figs. 57 B to 61). It 

 is obvious that the mechanical arrangement more or less necessi- 

 tates the approach of these chromosomes to the pole before the 

 others that are on the outer fibers, and this may be the only 

 explanation of this fact. However, in many cases, these two 

 small chromosomes seem to be connected by fibers, but it is im- 

 possible to be sure of this owing to the delicacy of the structures 

 concerned. In a polar view of the late anaphase, the two small- 

 est chromosomes are often to be found quite close together with- 

 in the ring of 12 other chromosomes (fig. 61). From the posi- 

 tion and behavior of the second small chromosome, I believe 

 that it is homologous with the second small one in the center in 

 N. undulata. 



In the' second division, a characteristic X Y pair is seen in the 

 center of the spindle, surrounded by a group of 12 chromosomes 

 arranged on the peripheral fibers (fig. 62 A, B, C). Among these 

 may be seen the two small chromosomes of the first division. A 

 polar view shows a ring of 12 chromosomes, including two small 

 ones, surrounding X or Y (figs. 63 and 64). These chromo- 

 somes are frequently found side by side in the metaphase as de- 

 scribed for N. glauca (fig. 65 A). Figure 67 A, B, shows a polar 

 view ofi two sister groups of chromosomes which have just sepa- 

 rated, these being taken from a rather thick section (7^), where 

 they were at different levels. 



The size relations of X and Y are quite variable, as will be no- 

 ticed by a glance at the figures. In some cases these chromo- 

 somes are almost equal, in others they are quite unequal (figs. 

 62 to 74). The sister groups, therefore, of the late anaphase, 

 are sometimes quite dissimilar in their chromatin content, with 

 respect to the central chromosome, and sometimes almost iden- 

 tical (figs. 75 to 77). In the spermatogonial groups, there are 

 26 chromosomes, including five large ones, four of which corre- 



