154 SCIENCE PROGRESS. 



key-note of cellular morphology. Much labour has been 

 spent in attempting to determine a boundary line between 

 such nuclear and cytoplasmic series proceeding on the 

 assumption that structures outside the nucleus are cyto- 

 plasmic, whether they persistently exist or arise in that 

 position, so long as they are not produced from dismembered 

 portions of the nucleus, the inverse of this definition being 

 applied to structures which are nuclear. 



In its simplest form the cytoplasm (protoplasm) presents 

 under a sufficiently high magnifying power the familiar, fine 

 reticulum which has been interpreted in many ways. Per- 

 haps the simplest, and certainly the most comprehensible, 

 hypothesis respecting its undifferentiated structure is con- 

 tained in Butschli's (2) conception of a " Schaumplasm," 

 i.e., it consists of an immense number of fluid o-lobules im- 

 mersed in a non-miscible fluid, so that in optical or actual sec- 

 tion it presents the appearance of a fluid reticulum. Under 

 the action of stains, the meshes of this net-work colour less 

 deeply than the strands, the stain being absorbed by fine 

 granules (microsomes) along their course, while the fluid of 

 which they are composed remains comparatively clear. 

 The manner of coloration of some of the microsomes is 

 similar to that of the interior nuclear mass, which also in its 

 normal condition is built on the same general plan, i.e., 

 when stained, it consists in optical section of a reticulum, the 

 colour being absorbed here by the chromatin granules, which 

 are immersed in clear threads of fluid (linin). All cells show 

 this gross structural division into nuclear and cytoplasmic 

 groups, and although either may be more or less masked by 

 the evolution of secondary structures during ontogeny, they 

 form the ground-work of cellular organisation through every 

 phase of life-history and metamorphosis. They are the 

 elements out of which these superadded structures are 

 evolved, and into which they again break down at the close 

 of individual existence. Of late years, however, much less 

 conspicuous, and less easily demonstrablecellular constituents, 

 have been held by many, as probably of the same prime 

 order. It is almost exactly twenty years since the able and 

 vanished naturalist Hermann Fol (5) drew attention to 



