152 KANSAS UNIVERSITY QUARTERLY. 



body in Xiphidhnn, beginning with the last division of the spermato- 

 gonia and following it through the formation of the spermatozoon. 

 In the spermatocytes, especially in the growth stage, it behaves very 

 much as in Bi'dr/nistola, with the exception that in the divisions of 

 Xiphidiuni it has the form of a curved chromatic body, to both ends 

 of which the spindle fibers attach, while in my object it is a straight 

 or slightly curved rod, receiving the insertion of the fibers at one end 

 only. In the spermatogonia he reports no vesicular stage or other 

 variation from its routine in the spermatocyte. 



Paulmier, 1899, describes a similar element ior AiidHa under the 

 name of the "small chromosome." He considers it present in the 

 resting stage of the spermatogonia in the form of two hazy, indefinite 

 masses of chromatin, not breaking down to the same extent as the 

 other chromosomes, and staining with the chromatin stains. In the 

 equatorial plate, these appear as two small chromatic bodies, very 

 much smaller than the other chromosomes, and connected with them 

 by chromatin bands. He says that in the period of spermatocyte 

 growth they reappear as a ''single body," but fails to describe the 

 manner in which their fusion is accomplished. The behavior of this 

 body in the sj^ireme stage is very similar, indeed, to that of the 

 accessory chromosome in the same stage in Brarln/Htold. In the latter, 

 however, it goes into the first spermatocyte division as a longitudinally- 

 split rod, not as a tetrad. 



As to the significance of this element, I am hardly prepared to 

 venture an opinion. McClung looks upon it as "possibly represent- 

 ing derivative substances from one or all of the chromosomes." 

 Paulmier offers the suggestion, somewhat along the same line, that it 

 may be an aggregation of ids representing characters at present being 

 lost by the sj^ecies, basing the supposition chiefly on the fact that, in 

 his material, it goes over bodily, without division, to one of the sper- 

 matids in the second spermatocyte division. My observations, it will] 

 readily be seen, are hardly corroborative of Paulmier's conclusions. 

 A glance at the figures shows the continuity of the element through-! 

 out all the stages, and a carefulness and precision in its movements 

 which are hardly compatible with the supposition that it is a degener- 

 ating chromosome. It is obvious that the term "small chromosome"] 

 is anything but descriptive of the element in BracJty.'^tola. 



Perhaps the most important thing to be gained at present from the! 

 knowledge of the behavior of the accessory chromosome in BTachis-\ 

 tola is the light which it throws upon the question of the individu^ 

 ality of the chromosomes. In the first place, the fact that it is a tru( 

 chromosome, though different from the others, is shown by its stain-j 

 ing reactions and by the parallelism between its development in the 



