CHROMOSOME GROUP IN BRACHYSTOLA MAGNA. 2/ 



first cell to the largest of the second, or the middle-sized pair (/V) of 

 the one to the middle-sized pair of the other. In these cells the 

 compact condition of the chromosomes will not permit of the 

 accurate recognition of individual elements --other than perhaps 

 the largest and the smallest in the group of sixteen, where size 

 differences are comparatively slight, but this deficiency will be 

 made up in the consideration of the group in the spermatocytes. 

 Throughout all the secondary spermatogonial generations, in 

 all stages except those of active division, the accessory chromo- 

 some remains apart in a vesicle which is virtually a separate 

 nucleus. The genetic relation of the accessory chromosome of 

 any secondary spermatogonium to that of any other in its line of 

 ancestry seems, therefore, unquestionable. Each of the sixteen 

 chromosomes of the larger group has also been enclosed in a 

 separate vesicle (Fig. 4) during the period of metabolic activity, 



FIG. 4. 



FIG. 4. Secondary spermatogonium in early prophase, showing very fine spiremes 

 arranged in their respective diverticula of the nucleus. Most of the partition walls be- 

 tween diverticula are shorter in the figures than in the preparation, since their cross- 

 ing if drawn in full would only cause confusion in a line drawing. (From a section.) 



but these vesicles are practically always in communication with 

 one another at their polar extremities, forming there a common 

 compartment in which the six smaller units are frequently found. 



