268 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



2. Progenetic Stage. 



The region occupied by the spindle remains distinctly 

 marked for some time owing to the fact that the cytoplasm 

 contained within it is less granular and less dense than the 

 rest (figs. 17-22). Throughout the entire cell the cyto- 

 plasm shows a marked tendency to a radial arrangement, 

 being denser in the neighborhood of the nucleus (fig. 17) • 



The first indication of spindle formation is the appear- 

 ance of granules (which stain violet) in the layer of 

 cytoplasm immediately adjoining the nucleus. They are 

 imbedded in the strands or fibres of the cytoplasmic net- 

 work and are first seen close to the nuclear wall, from 

 which they gradually extend outward into the cytoplasm. 

 They are at first irregularly scattered, but soon become 

 more numerous and more closely crowded together until 

 finally they appear to fuse together to form continuous 

 fibres which are at first granular and irregular in outline, 

 but gradually become regular and smooth in appearance 

 (fig. 18). 



3. Genetic Stage. 



The fibres so formed are attached to the nuclear wall 

 and their formation always begins at the wall and proceeds 

 outward towards the periphery of the cell. The fibres at 

 first are wavy and irregular and follow the outlines of the 

 cytoplasmic meshes, but gradually straighten out and come 

 to lie in a radial direction (fig. 19). Since these fibres go 

 to form the spindle, they will be called the genetic fibres. 

 The genetic fibres gradually increase (figs. 20 and 21) in 

 number and size — some being much larger and more prom- 

 inent than others — until the stage shown in fig. 22 (upper 

 half) is reached. They then begin to assemble in groups, 

 as shown in the lower half of the same figure, in which 

 various stages of the process are shown. So far as can be 

 judged from their appearance, the groups are formed simply 

 by a change in position of the fibres, whereby their free 

 ends gradually come together at certain places and finally 

 fuse to form cones. The location of the cones is variable; 



