CHROMATLW, LI XIX, AXD CYTOPLASM 303 



the achromatic network, the nuclear membrane, and the cell-mesh- 

 work have essentially the same structure, all consisting of microsomes 

 united by connective substance, and being only " parts of one and the 

 same structure." But, more than this, he asserted that the chromatic 

 and achromatic microsomes might be transfon/icd into one another, and 

 were tJiereforc of essentially the same morpJiological nature. " They 

 pass successively, in the course of the nuclear evolution, through a 

 chromatic or an achromatic stage, according as they imbibe or give 

 off the chromophilous substance." ^ Both these conclusions are borne 

 out by recent researches. Heidenhain ('93, '94), confirmed by Reinke 

 and Schloter, finds that the nuclear network contains granules of two 

 kinds differing in their staining-capacity. The first are the basi-chro- 

 matin granules, which stain with the true nuclear dyes (basic tar-col- 

 ours, etc.), and are identical with the " chromatin-granules " of other 

 authors. The second are the oxychromatin-granules of the linin-net- 

 work, which stain with the plasma-stains (acid colours, etc.), and are 

 closely similar to those of the cytoreticulum. These two forms gradu- 

 ate into one another, ajid are conjectured to be different phases of the 

 same elements. This conception is furthermore supported by many 

 observations on the behaviour of the nuclear network as a whole. 

 The chromatic substance is known to undergo very great changes in 

 staining-capacity at different periods in the life of the nucleus (p. Zl)^\ 

 and is known to vary greatly in bulk. In certain cases a very large 

 amount of the original chromatic network is cast out of the nucleus 

 at the time of the division, and is converted into cytoplasm. And, 

 finally, in studying mitosis in sea-urchin eggs I found reason to con- 

 clude ('95, 2) that a considerable part of the linin-network, from which 

 the spindle-fibres are formed, is actually derived from the chromatin. 



From the time of the earlier writings of Frommann ('65, '^'j\ 

 Arnold i^^j), Heitzmann ('73), and Klein i^']'^), down to the present, 

 an increasing number of observers have held that the nuclear reticu- 

 lum is to be conceived as a modification of the same structural basis 

 as that which forms the cytoplasm. The latest researches indicate, 

 indeed, that true chromatin (nuclein) is confined to the nucleus.^ But 

 the whole weight of the evidence now goes to show that the linin- 

 network is of the same nature as the cell-meshwork, and that the 

 achromatic nuclear membrane is formed as a condensation of the same 

 substance. Many investigators, among whom may be named From- 

 mann, Leydig, Klein, Van Beneden, Carnoy, and Reinke, have de- 

 scribed the fibres of both the intra- and extra-nuclear network as 

 terminating in the nuclear membrane ; and the membrane itself is 

 described by these and other observers as being itself reticular in 

 structure, and by some (Van Beneden) as consisting of closely crowded 



1 I.e. p. 583. 2 cf. Hammarsten ('95). 



