Mc CLUNG. 



[Vol. II. 



thread has become very short and thick and is bent in the 

 middle with an obtuse angle so as to resemble a boomerang. 

 At this time, it may be observed lying at one side of the circle 

 of chromosomes arranged in the equatorial plate, and plainly 



■X 



Fig. I. — Prophase of spermatogonia 

 showing the accessory chromosome, 

 marked " x," applied to the surface 

 of the nuclear vesicle. 



Fig. 2. — Later prophase of the sper- 

 matogonial stage in which the ac- 

 cessory chromosome has become 

 " U "-shaped. 



distinguishable from them by reason of its greater length (Fig. 3;. 

 From the pole the chromatin appears as a broad, fenestrated 

 plate, and the accessory chromosome is indistinguishable from 

 the ordinary ones (Fig. 4).^ Because of the rapidity of the 

 division none of the anaphases are to be seen, but in the telo- 

 phases the ordinary chromosomes of the cell may be seen 



Fig. 3. — Metaphase of the spermato- 

 gonia showing the accessory chromo- 

 some applied to the periphery of the 

 circle of chromosomes. 



Fig. 4. — The same stage as rep- 

 resented in Fig. 3, but viewed 

 from the pole. 



grouped in the typical manner at the two ends of the spindle, 

 while extending down towards the equatorial plate from each 



1 This peculiar arrangement of the chromatic mass is very striking, and is 

 clearly due to a strong concentration of the nuclear elements. When the broad 

 plate is cut squarely across, near one surface, the ends of the chromosomes may 

 be observed as isolated bodies, but near the center of the group they lose their 

 individuality in the mass. It is possible that the effect is due to improper fixation, 

 but since all the cells around the follicle containing the spermatogonia, and even 

 the cytoplasm of the spermatogonia themselves, is excellently preserved, this seems 

 hardly probable. 



