THE CYTOPLASM 



afforded by the appearance of the spindle and asters in cross-section. 

 In the early stages of the egg of Nereis, for example, the astral rays 

 are coarse anastomosing fibres that stain intensely and are therefore 

 very favourable for observation (Fig. 60). That they are actual fibres 

 is, I think, proved by sagittal sections of the asters in which the rays 

 are cut at various angles. The cut ends of the branching rays appear 

 in the clearest manner, not as plates but as distinct dots, from which 

 in oblique sections the ray may be traced inwards toward the centro- 

 sphere. Driiner, too, figures the spindle in cross-section as consisting 

 of rounded dots, like the end of a bundle of wires, though these are 

 connected by cross-branches (Fig. 28, F). Again, the crossing of 



Centrosphere con- 

 taining the cen- 

 trosome. 



Aster. 



Spindle. 



Chromosomes forming the equatorial plate. 



Fig. 21. Diagram of the dividing cell, showing the mitotic figure and its relation to the cyto- 

 plasmic meshvvork. 



the rays proceeding from the asters (Fig. 128), and their behaviour in 

 certain phases of cell-division, is difficult to explain under any other 

 than the fibrillar theory. 



We must admit, however, that the mesbwork varies greatly in differ- 

 ent cells and even in different physiological phases of the same cell; 

 and that it is impossible at present to bring it under any rule of uni- 

 versal application. It is possible, nay probable, that in one and the 

 same cell a portion of the meshwork may form a true alveolar structure 

 such as is described by Butschli, while other portions may, at the 

 same time, be differentiated into actual fibres. If this be true the 

 fibrillar or alveolar structure is a matter of secondary moment, and 

 the essential features of protoplasmic organization must be sought in 

 a more subtle underlying structure. 1 



1 See Chapter VI. 

 E 



