80 KANSAS UNIVERSITY QUARTERLY. 



13 ; but despite the multiplicity of their forms, these precursors of 

 the chromosomes are all referable to a common type. 



One thing of striking interest and importance to be observed at 

 this stage is the clear and unmistakable existence of the longitudinal 

 cleft in these segments. This may appear more or less clearly mani- 

 fest, as is shown in Fig. 12, but there is absolutely no doubt of its 

 presence. Owing to the various positions assumed by the chromatin 

 segments in the nucleus, the split is more easily observed in some than 

 in others or even in different parts of the segment, as is shown in Fig. 

 14. 



There is, in nearly every case, a weak place about the center of the 

 rod or loop. As a result of this, the thread often becomes bent upon 

 itself at an angle (Fig. 14), thus producing the double-V's described 

 by Paulmier. From the method of its formation and subsequent be- 

 havior, there is no doubt in my mind that this represents the place 

 where the chromatids of the second spermatocyte division are to 

 separate. Certainly the space between the arms of the Vs corresponds 

 to the longitudinal cleft of the thread and to the plane of cleavage in 

 the first spermatocyte division. 



The subsequent behavior of these peculiar elements is very inter- 

 esting and offers us a key by which we may determine whether or not 

 the separation of the chromatids effected by the first spermatocyte 

 division is longitudinal or cross. It is at this point where the greatest 

 difference of opinion concerning the behavior of the chromatin ele- 

 ments exists, and I shall, therefore, speak in detail of the changes now 

 ensuing, in the hope that the observations I have made upon the ex- 

 tremely favorable objects at my command may serve to aid in bringing 

 together and unifying the diverse results obtained by other investi- 

 gators who have not been so fortunate in the quality of their material. 

 The conclusions herein set forth have been reached only after careful 

 and painstaking observations and I feel convinced of their accuracy. 



The method by which the tetrad elements are formed is particularly 

 shown in Figs. 14, 15, 15a, and 17. The planes of the two resulting 

 cleavages are clearly indicated in the double-V figure represented in 

 Fig. 14. This will serve as a type figure to which we may refer various 

 modifications for explanation. Instead of being bent at the middle, 

 the element may maintain the form of an approximatel}' straight rod. 

 in which case the point of cross-division is not always apparent. 

 Again, the free ends of the rod may curve around until they come in 

 contact, thus producing the occasional ring figures to be observed in 

 various stages of the first spermatocyte prophases. These latter are 

 particularly valuable in the determination of the longitudinal charac- 

 ter of the first division. 



