64 RISEN. [Vol. XVII. 



dark-staining bodies, one of which enters the granosphere and 

 becomes the archosome, while the others remain as accessory 

 archosomes. The archosome, as well as the accessory archo- 

 somes, divides. The two-centrioled archosome soon rises above 

 the granosphere and carries with it a part of that sphere (Fig. 

 35). Metaplasmic secretions have also appeared among the 

 granules of the two spheres. The central spindle is formed 

 by the separation of the two centrioles and by the supplying 

 of material from the granosphere to the rays formed between 

 the two archosomes. The polar rays, or fibers, and the mantle 

 fibers are formed at about the same time. The contractile fibers 

 are formed, partly at least, of a different material and are from 

 the beginning of different structure, being beaded and of a con- 

 tractile nature. The relative position of the central spindle 

 and the nucleus is alone dependent on the relative position of 

 the granosphere and the central spindle. The central spindle 

 is always so situated that a plane passing through its equator 

 also passes through the granosphere. Numerous accessory 

 archosomes have formed which probably assist in the forma- 

 tion of the contractile fibers. There is always one, sometimes 

 two archosomes at each pole of the central spindle. Before 

 the poles of the central spindle have reached the opposite sides 

 of the nucleus, the nuclear membrane has been destroyed by 

 rays of the mantle fibers (Figs. 41-47). Shortly afterwards the 

 chromosomes are thrown on the central spindle and taken hold 

 of by the contractile fibers. After the anaphase or mitosis is 

 over, a cytoplasmic membrane is formed around the nucleus, 

 and as this membrane is being pulled away by a set of fiber 

 cones a vacuole is formed around the nucleus in which the 

 nucleus has ample room to develop. These fiber cones are 

 often numerous and as high as seventeen in a single cell. The 

 cones are formed as follows. The accessory archosomes ap- 

 pear on the cytoplasmic membrane, and fibers are projected in 

 various directions on the membrane. The archosomes then 

 rise above the membrane, pulling with them the fibers, which, 

 however, remain attached to the membrane with their distal 

 ends. The cones rise so far as to project high above the 

 regular circumference of the cell (Fig. 69). This formation 



