676 C. E. McCLUNG 



would seem probable that this changed external relation is the 

 result of internal organization. Whatever be the cause the 

 results are definite and exact. 



During the prophase, indications of change are wanting until 

 in the late stages, but upon the establishment of the full mitotic 

 figure marked differences in appearance of certain chromosomes 

 are at once apparent. These are perhaps not so prominent in 

 polar views, although the familiar clear rings are wanting and the 

 common V-shaped elements are few, but regarded laterally most 

 striking differences at once appear. The prophase rings, whi(?h 

 later were missing in their customary position in the equatorial 

 plate when viewed from the pole, are very evident now, extended 

 instead, at right angles to this position (figs. 63 and 64 a, 66), 

 and there are unfamiliar E-shaped chromosomes (fig. 65) and 

 asymmetrical rings (fig. 64 g). Occasionally there are rings lying 

 in the plane of the equatorial plate where they form part of an 

 E-shaped element, as is represented by the large chromosomes 

 at the left of figure 63. There are also elongated rods with bent 

 ends (fig. 64 b) and among these unusual forms appear the com- 

 mon rods and crosses (figs. 63, 64 e, 64 f, 65). The accessory 

 chromosome, instead of being rod-shaped and going thus to the 

 pole of the spindle, is V-shaped with fiber attachment at the 

 center (fig. 66). 



An analysis of these conditions, in comparison with the sper- 

 matogonial chromosomes which enter into the first spermatocyte, 

 and with the second spermatocyte chromosomes which emerge 

 from it, gives definite evidence of the cause underlying the changed 

 conditions in these species. Primarily they seem to be due to a 

 shifting of the fiber attachment from the end of the chromosome 

 to the middle or to some intermediate point, as was described for 

 the spermatogonia. Whatever the position of the fiber inser- 

 tion in the earlier generation it is carried over into the first sper- 

 matocyte and appears again in the second spermatocyte. If this 

 be at the center of the chromosomes when they join in synapsis, 

 fusion takes place at both ends producing a ring with a possible 

 divergence of the chromatids at each contact end. If such 

 lateral extensions occur they must disappear later when the halves 



