THE ACCESSORY CHROMOSOME. 59 



the vesicular stage, and this only, since at all other times it stains 

 a bright red. The absence of the formation of a spireme at any 

 stage in the development of this element is paralleled by Henk- 

 ing's description of the normal process in all the chromosomes in 

 the spermatogonia of Pyrrhocoris. 



54. " Perhaps the most important thing to be gained at present 

 from the knowledge of the behavior of the accessory chromo- 

 some in Brachystola is the light which it throws upon the question 

 of the individuality of the chromosomes. In the first place, the 

 fact that it is a true chromosome, though different from the 

 others, is shown by its staining reactions and by the parallelism 

 between its development in the spermatogonia and that of its 

 more generally recognized fellows. Although it shows a tend- 

 ency to lag behind the other chromatic bodies, the only radical 

 difference between the two is the absence of the loose spireme 

 in the accessory, and this is paralleled, as shown above, by the 

 normal process of all the chromosomes of Pyrrhocoris, according 

 to the statement of Henking. The apparent radical difference in 

 the case of the vesicular stage is, in reality, only a matter of 

 degree, for it frequently happens that the ordinary chromosomes, 

 in going into the diffused condition, leave a very appreciable 

 hollow in their centers (Fig. 30). Apparently there is, for some 

 reason, a necessity that the chromatic granules of the accessory 

 come into closer relation with the cytoplasm than those of its 

 mates, and the result is their deposition upon the vesicle itself 

 this vesiculation being really a substitute for the loose spireme so 

 conspicuously lacking. 



55. " Now, if it be admitted that the body is a chromosome, 

 inspection quickly shows us that it maintains throughout the 

 spermatogonial divisions, as well as in those that follow, an indu- 

 bitable independence, being enclosed, in all stages except those of 

 actual division, in its own individual membrane. Having, then, 

 one of the chromosomes which preserves its individuality in this 

 way, and seeing the other chromosomes enclosed for a part of 

 their development in similar individual vesicles, which only be- 

 come intercommunicating by absorption of a part of their walls, 

 have we not a right to suppose that at one time they too enjoyed 

 the same independence as their more exclusive mate ? In other 



