548 



of the iron-haematoxylin is stopped relatively early the remainder of 

 the nucleus appears to be filled with a homogeneous or very finely 

 granular substance staining much less deeply than the nucleolus. Some- 

 times one or two small bodies stained like the nucleolus may be seen. 

 In order, however, to obtain clear views of amitotic divisions it is 

 necessary to carry the extraction farther until the stain is almost or 

 completely extracted from all the nuclear contents except the nucleolus 

 and in some cases the smaller bodies, above mentioned which behave 

 like the nucleolus with respect to stains, but, owing to their small size, 

 often lose their color before the latter. Under these conditions only 

 the nucleolus is visible in most cases as indicated in the figures. The 

 nuclei of different regions and tissues present no characteristic dif- 

 ferences except as above mentioned in the later stages of the sexual 

 cells. The cytoplasmic structures afford the only means of distinguishing 

 the various regions. 



The earliest visible indication of amitotic division is the appearance 

 of a delicate dark line extending across some part of the nucleus. 

 Various examples of this appear in Figure 1. By careful focusing 

 this line may be followed in favorable cases completely around the 

 nucleus and an optical section of the nucleus shows that it is a slight 

 constriction. In most cases a small dark body staining like the nucleolus 

 and presumably a new nucleolus may be seen on one side of the con- 

 striction while the large nucleolus appears on the other: often two 

 or three of these small bodies are seen, sometimes appearing as if in 

 contact with the nuclear membrane along the line of the constriction 

 (Fig. 5 b, Fig. 11a). These appearances are frequently due doubtless 

 to the retention of the stain in some minute fold or denser portion 

 in which extraction is less rapid than elsewhere, but the new nucleolus 

 can be distinguished without difficulty either at this stage or a little 

 later since it soon becomes larger than the other bodies. Figures 1, 

 6, and 7 afford numerous examples of various stages. Whether the 

 new nucleolus arises in all cases from the old I have been unable to 

 determine with certainty. Nucleoli are frequently seen with a minute 

 body in contact with their surface as in Figure 7 b, and often as in 

 Figure 11a the old and new nucleolus appear close together on the 

 two sides of the constriction. Other cases show them widely separated 

 (Fig. 4 a und b. Fig. 9), but these appear to be later stages. On the 

 other hand, it is sometimes impossible to find more than the one 

 nucleolus in dividing nuclei (Fig. 7, two cases near middle). I think 

 it not impossible that the new nucleolus may, in some cases at least, 

 arise independently of the old. 



