THE WONDERS OF LIFE 



cells — but not all — have the appearance of vesicles, 

 having a thin skin enclosing a liquid content, the nuclear 

 sap. The achromin then usually forms a frame-work of 

 threads, with chromatin granules in its meshes or 

 knots, within this round vesicle. This very thin nuclear 

 membrane (often only visible as its contour) or cary- 

 otheca may be regarded as the result of surface-strain 

 (at the planes of contact of caryoplasm and cytoplasm). 

 The watery and usually clear and transparent nuclear 

 sap (caryolymph) is formed by imbibition of watery 

 fluid (like the frothy structure of the plasm in general). 

 The separation of the nuclear membrane and nuclear 

 sap is not a primary property of the nucleus, but is due 

 to a secondary differentiation in the originally homo- 

 geneous caryoplasm. 



Like the caryoplasm of the nucleus, the cytoplasm of 

 the cell-body is originally a chemical modification of the 

 simple and once homogeneous plasm (the archiplasm). 

 This is clearly shown by the comparative biology of the 

 protists, their unicellular organism presenting a much 

 greater variety of stages of cell-organization than the 

 subordinate tissue-cells in the bodies of the multicellular 

 histona. However, in the great majority of cells the 

 cytoplasm is separated into several, and frequently very 

 numerous, parts, which have received diverse forms and 

 functions in the division of labor. We then see very 

 conspicuously the regularity of cell-organization, which 

 is altogether wanting in the simple homogeneous plasma 

 granules of the monera. As this great differentiation 

 of the advanced elementary organism is incorrectly 

 generalized by some recent cytologists and described 

 as a universal feature of cells, it is necessary to insist 

 explicitly that it is a secondary phylogenetic develop- 

 ment, and is altogether wanting in the primitive or- 

 ganisms. The complexity of the physiological division 

 of labor and the accompanying morphological separation 



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