666 C. E. McCLUNG 



be possible to assert unequivocally that the longitudinal axes 

 of the paired chromosomes of the first spermatocyte represents 

 the coincident axes of the spermatogonia! chromosomes consti- 

 tuting it, for if there be a parasynapsis at any period there is a 

 possibility that the doubly split thread may open out along the 

 plane of the equational cleavage instead of along the space be- 

 tween chromosomes. In either event the form of the resulting 

 chromosome would be the same. There are however some cri- 

 teria for judging such relations and these, taken in consideration 

 with the movements of the chromosomes in the spermatogonia! 

 divisions, make it appear highly probable that the evident telo- 

 synapsis of the late prophase actually exists as such. 



Two observations strongly support this conclusion. There 

 is first the case of the unequal tetrad, where two spermatogonia! 

 chromosomes of unlike size are joined together end to end. If 

 the chromosomes are persistent individuals there can be no ques- 

 tioning this relation. Again, in the multiple chromosome, we 

 have established the coincidence of the longitudinal cleft of the 

 accessory chromosome with that of the tetrad to which it is joined. 

 Because the accessory chromosome is a simple spermatogonia! 

 element its plane of cleavage is determined beyond doubt, and 

 since in the spermatogonia it is joined end to end with one-half 

 of the tetrad, the latter's cleft is identified. The remaining mem- 

 ber must, of necessity, be joined by its end to its mate and so 

 continue its division plane with that of the other members of 

 the multiple. An additional, though less obvious piece of evi- 

 dence, is furnished by a comparison between the chromosomes, 

 especially the annular ones, of Hippiscus and Stenobothrus. It 

 seems evident that there are here two types of division for cer- 

 tain chromosomes, provided the earlier history of each is the 

 same. All the structural relations are similar in these two cases 

 except the position of the fiber attachment and it is difficult to 

 believe that their early history is different. If they are similarly 

 constituted then the presumption is strong that those which lie 

 with their length in the equatorial plate of the first spermatocyte 

 are divided along their longitudinal cleft while those placed in 

 the axis of the spindle with fiber attachment midway between 



