FORMATION OF THE FIRST SPERMATOCYTE CHROMOSOMES 575 



mens and there the unequal pair arises from the nucleolus in the 

 prophases of the first spermatocyte division. A study of side 

 views of metaphase plates of the first division indicates that we 

 might have a case of a single unpaired idiochromosome. This 

 seems very doubtful, however, since the behavior of the single 

 chromosome in the maturation divisions is irregular. Its be- 

 ha\'ior is similar to that of the single chromosomes in the other 

 individuals. Figure 7, D, G, H, I and / are anaphases of the 

 first division and, I think, show clearly that this chromosome 

 may pass to one pole undivided (G) ; that it may divide, one part 

 passing to one pole and one to the other (7), or that it may 

 constrict as if to divide and in this manner pass to one pole (/). 

 Counts of the second division, metaphase plates, show 34 cells 

 with 13 chromosomes and 34 with 12. This indicates an approxi- 

 mate equal distribution of the single chromosome. In ana- 

 phases of the second division (fig. 7, K and L) a single lagging 

 chromosome is likewise present and no doubt it may or may not 

 divide. My figures do not show it in division, but Zweiger ('06) 

 and Stevens ('10) show a lagging chromosome in the second divi- 

 sion which divides. Figure 7, L, is interesting in that it shows this 

 chromosome very much elongated. In such cases it seems very 

 doubtful w^hether it ever reaches either pole. 



Formation of the first spermatocyte chromosomes 



During the greater part of the grow^th period, and possibly 

 all of it following synapsis, the chromatin threads appear double 

 and made up of two rows of granules (plate 1, fig. 1). From these 

 chromatin threads the dumb-bell-shaped spermatocyte chro- 

 mosomes are formed. One of the intermediate stages in this 

 transformation is a more or less typical ring, and it is the for- 

 mation of this ring with which I am principally concerned. Two 

 methods of ring formation have been described. Let us leave 

 out for the present the question whether the longitudinally split 

 thread is formed from chromosomes which have united end to 

 end or side by side. One method is by the bending of the thread 

 until the free ends come in contact. This method has been 



JOURNAL OP MORHHOLOGY, VOL. 25, NO. 4 



