INDIVIDUALITY OF CHROMOSOMES. 3 



Thus one cyst will have most cells in the metaphase but a few 

 will be in early anaphase, while the neighboring cyst in the next 

 follicle may have most of the cells in late anaphase but a few 

 will be in early anaphase. The precocious cells in one cyst con- 

 nect directly with the laggards of another. This is a great ad- 

 vantage for correct interpretation of the appearances. 



OBSERVATIONS. 



The accessory chromosome appears in the earliest secondary 

 spermatogonial divisions. During mitosis it takes its place in 

 the periphery of the equatorial plate (Figs. I and 2). It always 

 has a bend at the center, and the whole is in the shape of an 

 irregular horseshoe (Fig. i)or its two ends are spread out almost 

 straight so that it is a straight rod with a short semicircle-like 

 bend at the center (Fig. 2). As the other chromosomes split 

 and pass to the poles the accessory also splits longitudinally 

 (Fig. 3). The curves of the horseshoe-like rods separate first 

 and the ends of the two daughter chromosomes are the last part 

 to be separated, as indicated by McClung (16), in Xiphidium. 

 All through the metaphase and anaphase the accessory is quite 

 a little behind the others. Its ends are sometimes scarcely 

 separated when the other chromosomes have reached the poles. 

 During the rest stage it does not become granular and disappear 

 like the others but remains a darkly staining mass. 



In the early growth period while the other chromosomes 

 become diffuse, the accessory takes its position against the wall 

 of the nucleus. Here it lies a strongly staining mass adherent 

 to the one side. Through all the long growth period the 

 accessory can be distinguished from the nucleolus by its stain 

 for a part of the time (Fig. 10), but it can be recognized all the 

 time by its position as it lies flattened against the outer wall. 

 The nucleolus, which for a part of the growth period takes the 

 same stains as does the accessory and just as readily, can usually 

 be distinguished by its rounded or oval shape. Its position in 

 the nucleus varies with almost every cell. It may be in the 

 center or near the periphery, opposite the accessory (Figs. 4, 5 

 and 8) or near to it (Figs. 6 and 7). It often lies against the 

 accessory or even partly over it (Figs. 6 and 10). This fact led 



