SUTTON : SPERMATOGONIAL DIVISIONS IN BRACHYSTOLA MAGNA. 151 



This being the case, it is not remarkable that Henking should 

 have passed over a body which, in his material, probably very closely 

 resembled the other chromosomes. In the growth stage, however, he 

 describes it (under the name nucleolus) in a way which makes its 

 equivalence to the accessory chromosome of Bi'ar/ujHtola unmistak- 

 able. So far as I have been able to discover, Henking is the first to 

 describe or figure this element. 



Vom Rath, 1892, probably saw the accessory chromosome in 

 Gr;/llotalpa, but his mention of it is so brief and vague that we can 

 only surmise as to its identity with the structure so prominent in the 

 Orthoptera. His only description of it is this, taken from his account 

 of the maturation period: "Ein Nucleolus ist bis in dies Stadium 

 deutlich wahrnelimbar geblieben. wahrend ein zweiter vrdlig unsichtbar 

 geworden ist. So viel steht fest, dass die Nucleoli an dem Aufbau 

 des Chromatischen Fadens, keinen directen Antheil nehmen." 



Wilcox, 1895, in Caloptenus, figures the accessory chromosome 

 (fig. Ill) in the spireme, stage of the spermatocyte, where I have seen 

 it plainly in the same material, but makes no reference to its presence 

 in the spermatogonia, unless the following statement should refer to 

 it: '"In fig. 10(5 there is a body (nucleolus?) which seems to have 

 recently divided." 



Moore, 1895, describes in Elasruahi'duchs the appearance of a 

 "secondary nucleolus" surrounded by its vacuole at the beginning of 

 the second spermatogenetic period (growth stage of the spermatocyte) . 

 This is the stage in which the accessory chromosome is most promi- 

 nent in insects, and it is probable that Moore's discovery in the fishes 

 corresponds to it. Another nucleolus is also present. Of the two 

 he says: "These two peculiar forms are always to be found after the 

 transition from the first to the second spermatogenetic period, and 

 throughout all the generations of the latter." In his figures the 

 'secondary nucleolus" has decidedly the aj^pearance of the accessory 

 chromosome of insects. 



Julian Wagner, 1896, describes for the spiders a structure which, 

 from its behavior in the first spermatocyte division, is certainly very 

 ike the accessory chromosome. He made no study of the spermato- 

 gonia. 



Montgomery, 1898, describes for Peittafoma a structure which 

 irises from one of the chromosomes of the last spermatogonial divi- 

 sion, and may be plainly seen throughout the spermatocyte divisions. 

 He calls it the "chromatin nucleolus," and there can hardly be a doubt 

 that it corresponds to the accessory chromosome. 



McClung, 1899, in the paper in which he proposes the name "acces- 

 ory chromo.some," gives an extended description of the behavior of this 



