654 C. E. McCLUNG 



ing has been lost from the cell and, so far as the morphological 

 identity of the chromosomes is concerned, no difference exists 

 except their pairwise union. 



The important phenomena of the synapsis stage will receive 

 consideration in later papers by my students and myself. At the 

 present time I wish merely to consider the comparatively simple 

 conditions apparent in the late prophase of the first maturation 

 division and in the succeeding mitoses. This is an important 

 matter because from studies of these stages, and upon practically 

 identical material, all the possible interpretations of the matura- 

 tion divisions have been advanced. Diversity of opinion regard- 

 ing maturation phenomena in unlike materials may therefore be 

 due, as in this case, not to differences in fact but merely to variety 

 of interpretation. Also, regardless of the exact nature of the 

 synaptic changes it is of great importance to know just what takes 

 place in the maturation mitoses, for often a correct interpretation 

 of the prophase chromosomes is followed by a faulty account of 

 their actual division later. No matter how accurately the proc- 

 esses involved in the formation of the tetrads is understood, 

 there could be no solution of the problem of chromosome dis- 

 tribution in the maturation divisions so long as the present un- 

 certainties regarding their movements continue. I therefore 

 desire, in this paper, to discuss the actual movements of the 

 chromatids, regarding it as determined that in the tetrads we 

 have a fusion of homologous chromosome pairs longitudinally 

 divided. 



I shall attempt therefore a comparative presentation of the 

 conditions during these later phases of the process, and shall 

 venture a critical consideration of the papers of other authors 

 on the same subject in the hope that a consensus of opinion may 

 be reached. I venture to hope also that my long study of this 

 subject, my extensive comparative acquaintance with Orthop- 

 teran material and the consistent results of my students may be 

 taken into consideration in judging my effort to arrive at some 

 conclusion in these disputed matters. 



