SPERMATOGENESIS IN THE ALBINO RAT 147 



and figure 57. This arrangement on the spindle may apparently 

 be either as shown in figure 57 or in the position of having 

 rotated 90 degrees, so that a lateral view of the spindle reveals 

 this chromosome as a ring still having its knob, or the appearance 

 given in figure 40. This position is found in oblique views of the 

 spindles so cut as to have removed some of the chomosomes. 

 When all are present, these refined observations cannot be made 

 since the various members of the complex lie so closely together. 

 The polar views of the cross in metaphase are even more trouble- 

 some. (See notes on figure 18 under description of figures.) 



I have had no opportunity to trace the early history of the 

 formation of the cross. Until ^uch observation is made I am 

 inclined to accept its formation as that shown by McClung ('14) 

 and Wenrich ('16) for the cross in Orthopteran complexes. 



That the small rings are also tetrad in formation must be 

 iaccepted on the evidence shown in figure 27. Mention may also 

 be made of the fact that none but small rod-like forms, with 

 or without humps, appear in lateral views of the metaphase com- 

 plexes. In polar views these small chromosomes appear round 

 or oval, as in figures 18 to 20. The triangular-shaped masses in 

 anaphase, although too minute to show the arms of the V, 

 furnish additional evidence that they are of similar organiza- 

 tion with the larger rings. 



The large chromosomes are always the last to divide. They 

 are to be seen in late anaphase stretching along the spindle be- 

 tween the chromosomes that have divided and are assembling 

 at the pole. Sometimes three or even four are thus found. The 

 last two to divide are B and A . The appearance of one of these 

 is shown characteristically in figure 22. Others present in this 

 particular cell were not drawn. 



Two points of interest remain to be noted. First, the terminal 

 attachment of the spindle fiber is common to all of the chromo- 

 somes, as it was in the spermatogonia. This fact accounts for 

 the simple V's in anaphase rather than the double ones seen in 

 such forms as the Stenobothrus type described by McClung 

 ('14). The second point is that no V's have been seen in polar 

 views at metaphase. The V-formation occurs at this stage in the 



