284 KANSAS UNIVERSITY SCIENCE BULLETIN. 



ZOOLOGICAL LABORATORY. 



parts are present and in the same relation to each other. Of 

 course now the chromosomes have the spindle fibers attached 

 to them at the synaptic points {XX). In the arrangements of 

 the group in the metaphase plate, the larger chromosomes, the 

 rings and bent rods, usually lie on the outside and the smaller 

 chromosomes nearer the center. The number in the first sper- 

 matocyte, without a single exception, was found to be twelve. 

 Of the group, the three or four extremely large members, the 

 three small ones and the accessory (No. 5) may quite readily 

 be recognized. In polar views of the cell-plate the accessory 

 is very often seen in cross-section or from a very oblique side 

 view. But it can usually be recognized with very little trouble, 

 since it almost always lies near the periphery of the plate and 

 shows no tendency toward division at this time. 



Figures 34, 35 and 36 are lateral views, showing the acces- 

 sory in its characteristic position. All the other chromosomes 

 are in the act of dividing. It is starting ahead of them, un- 

 divided, to one of the poles. It may at one time have been in 

 the equatorial plate along with the others, but now, as may be 

 seen by the figures, it is moving out. In a close examination 

 of the spindle it is found that each of the ordinary chromo- 

 somes is attached by means of a single fiber to each pole. The 

 fiber, as before said, fixes itself at the point (X) on the chro- 

 mosome where the future reductional division will take place. 

 In the case of the accessory there is only one fiber, that con- 

 necting it with the pole towards which it is traveling. Its 

 opposite end is entirely free of fibers. 



In figures 37-39, anaphases of the first division, there is 

 clear evidence that the accessory does not divide but passes 

 over, as it is, to one of the resulting daughter-cells. Figure 37 

 shows all of the remaining chromosomes dividing or divided. 

 The largest one, chromosome No. 12, seems to be much twisted, 

 but nevertheless the four parts to it may be easily made out. 

 The chromosomes in this drawing have been displaced some- 

 what to right and left in order to show them more clearly. 

 They occupy, however, the same relative position with respect 

 to each other that they did in the cell, although spread out over 

 a greater area. Figures 38 and 39 are still later anaphases, 

 showing eleven dyads at one pole and their eleven mates, plus 

 the accessory, at the other. The halves of the accessory (No. 

 5, figs. 38 and 39) as it nears the pole seem to be inclined to 



