92 C. F. MARSHALL. 



histologists, that they are protoplasmic in nature, and denser than 

 the rest of the cell. 



"We have first to consider the nature of intracellular networks in 

 general, and whether their function is an active or a passive one. In 

 the case of intranuclear networks, the changes which the network 

 undergoes in karyokinetic division of the nucleus point to their being 

 of an active nature. The extranuclear network (intracellular) is 

 apparently of the same nature as the intranuclear, since the two have 

 been shown to be continuous in many cells ; and also they have the 

 same behaviour towards stains and reagents. Moreover, if intra- 

 cellular networks are developed by a process of vacuolation of the 

 protoplasm of the cell, or a division into denser and less dense parts, 

 as described previously when treating of the Protozoa, it is obvious 

 that in these cases the network must be the active and the contractile 

 part of the cell. 



The continuity and identity of nuclear and extranuclear networks 

 is strongly supported by Sedgwick's remarkable observations on the 

 early stages of Peripatus.* He not only demonstrates the con- 

 tinuity of the extranuclear and intranuclear networks, but he also 

 shows that during segmentation of the ovum the cells do not become 

 completely separated, but remain connected by their protoplasmic 

 networks, i.e., that the intracellular networks of all the cells are 

 continuous. 



He also states that the so-called nuclear membrane is reticular in 

 nature, and not a true membrane, being, in fact, part of the general 

 reticulum of the cell. In the cells described by Sedgwick there is no 

 doubt that the reticulum is the active portion of the cell, for the rest 

 of the cell consists simply of vacuoles. 



Flemming states,! as Sedgwick also noticed, that the first change 

 observable in a cell whose nucleus is about to divide is in the extra- 

 nuclear protoplasm. Strasburgeri further states that the fibrils 

 which form the nuclear spindle originate in the surrounding "cyto- 

 plasm " at the time of division. This appears to be direct evidence 

 of an active function in the intracellular network. 



* " Quart. Journ. Micr. Sci.," vol. xxvi., 1886, pp. 175—212. 

 t " Zellsubstanz, Kern u. Zelltheilung," Leipzig, 1882. 



t "Arch. f. Mikr, Anat.," Bd. xxiii., "Die Controversen der indirecten Kern- 

 theilung," 



