MUSEUM OF COMPARATIVE ZOOLOGY. 355 



condition of nuclei. It is in preparation for the coming division, and for 

 the purpose of accumulating this substance, that all the forces of the 

 cell are concentrated, thus compelling a cessation of the migratory activ- 

 ity of the karyokinetic mass just before division. This accumulation of 

 nuclear fluid is a process of nutrition, effected under the attractive 

 influence of the nucleus, and the systems of rays are an evidence of the 

 existence of this nutritive process. These solar figures have, after all, 

 the same physiological significance, whether they are composed of stout 

 or slender rays. 



The last structure produced by the karyokinesis — the hollow cask — 

 is composed of diff'erent elements. The fibres and rods divide directly, 

 but the contents of the cask, which are not of a protoplasmic nature, 

 are not capable of direct separation, owing to their viscidity ; but dur- 

 ing elongation fine granules, which are embraced by the cask, form 

 themselves into filaments. These, however, are karyokinetic granules, 

 which were not employed in the construction of the staves of the cask. 



The last admission seems to me to remove all reasonable ground for 

 a distinction between the peripheral and the central fibres of the cask- 

 like stage of the nucleus. 



New nuclei are formed, not by a differentiation of the homogeneous 

 mass simply, but by a disintegration brought about by renewed motion. 

 Notwithstanding the important influence of the nuclear sap in the for- 

 mation of new nuclei out of the karyokinetic halves, the latter, re- 

 maining unchanged, are employed in the production of the nuclear 

 membrane without experiencing the influence of the sap (!). The con- 

 - struction of the membrane out of rods and granules is the cause of its 

 punctate appearance when seen in optical section. 



The second division of Flemming's ('78^) paper deals with cell division 

 in tissues, both normally growing and inflamed. In the division of the 

 epithelial cells of the caudal fin and the gill-plates of Salamandra, he dis- 

 tinguishes a series of phases.* 



Phase 1. There arises a "basket trestle" of closely coiled, exceed- 

 ingly fine filaments, which gives the living nucleus the appearance of 

 being finely granular, and as such it has usually been described. No 

 evidence of nucleoli is to be found, but the nuclear figure has a sharp 

 limitation toward the protoplasm. As compared with the network, or 

 trestle, of the quiescent nucleus, it is much closer (i. e. has finer 

 meshes), more evenly distributed through the substance of the nucleus, 

 and represents a greater mass of substance. Is it directly connected in 



* The order of their succession is considered later. 



