THE MINUTE ANATOMY OF THE CELL. 



ulum, like a sponge ; by others as more nearly like an emulsion 

 or foam, consisting of a more solid framework enclosing innu- 

 merable minute separate spherical cavities filled with liquid ; by 

 others still as composed of unbranched threads running in all 

 directions through a more liquid basis ; but its real nature is still 

 unknown. 



It is evident that the visible structure of protoplasm gives no 

 hint of its marvellous powers as the seat of vital action, and we 

 are therefore compelled to infer that it is endowed with a chemi- 

 cal and molecular constitution extremely complex, and probably 

 far exceeding in complexity that of any lifeless substance. 



The Nucleus is a rounded body suspended in the cell-sub- 

 stance ; it is distinguishable from the latter by its higher refrac- 

 tive power, and by the intense color it assumes when treated 

 with staining fluids. It is surrounded by a very thin membrane, 

 and consists internally of a clear substance (aehromatin), through 

 which extends an irregular network of fibres (chromatin). It 

 is especially these fibres which are stained by dyes. In the 



FIG. 13. (After Sachs.) Young growing cells from the extreme tip of a stonewort 

 (Chara). w, membrane; H, nuclei; p, protoplasm; r, vacuole filled with sap. 

 (X550.) 



meshes of the network is suspended in many cases a second 

 rounded body known as the nucleolus, which stains even more 

 deeply than the network itself. 



The Membrane or Wall of the cell forms a rather thick sac, 



