64 McCLUNG. 



erations of the testis, and (4) to suggest a theory in explanation 

 of its function. 



Confirmation of the statement that most references to the ac- 

 cessory chromosome would be found under discussions of nucle- 

 olar structures has just been given in the quotations from various 

 papers. When a reason is sought for the classification of such a 

 purely chromosomic element with this heterogeneous group of 

 bodies it is difficult to find any that is sufficient. Interest in 

 other problems has, perhaps, induced investigators to concen- 

 trate their attention elsewhere and as a result the accessory chro- 

 mosome has been assigned .relationships entirely foreign to its 

 true nature. 



I have, in previous papers ('99, 'oo), given my reasons for re- 

 garding it as a chromosome, so that I shall not have to go much 

 into detail on this point. It would seem sufficient to show that 

 the element is a chromosome of the spermatogonia (1" 27, 41, 

 47, 4953) and that it divides in a subsequent spermatocyte 

 mitosis as a chromosome (T[ 33, 36, 42, 47, 48) in order to in- 

 sure its classification as such. Yet in full recognition of these 

 conditions Montgomery (1 27) calls it a nucleolus and insists 

 (^[ 29) that it never again (z. e., in the spermatocytes) becomes 

 a chromosome. While Henking fails to detect the origin of his 

 " nucleolus " from a chromosome of the spermatogonia he recog- 

 nizes its chromatic character and its participation in the act of 

 metakinesis and even occasionally calls it a " chromatinelement " 



(i 13). 



Wilcox (If 19) is very careful to note the staining reaction 

 of the nucleolus and that of the chromosomes. This he finds to 

 be identical except in certain stages, and in these, it is the chro- 

 mosomes proper that weaken in their affinity for the basic ani- 

 lines while the "nucleolus" consistently reacts to them with the 

 true chromatin reaction. But in considering the " nucleoli " of 

 the spermatocytes (^ 20) he regards them as such because 

 "they react to the stains quite differently from the chromosomes." 

 Just in what respect this difference lies is not quite manifest from 

 the text, but it is apparently in being uniform in staining instead 

 of variable. 



In his early paper Wilcox ('95) does not trace the final history 



