CELL-NUCLEUSFERTILISATION 227 



The nucleus is perhaps the most important 

 organ of the cell. There are strong grounds 

 for believing that it is largely concerned in the 

 determination of those hereditary qualities 

 which distinguish one species from another; 

 and we are also well aware of its great import- 

 ance in governing the chemical changes which 

 proceed within the protoplasm. 



The nucleus consists, essentially, of a 

 variety of substances, more or less gelatinous 

 in consistency. These, together with more 

 fluid constituents, are contained within a 

 membrane, and are thus sharply delimited 

 from the surrounding cytoplasm. The con- 

 tents of the nucleus are not homogeneous. 

 One or more spherical bodies, the nucleoli, 

 may often be seen inside it. These, although 

 often very prominent, are of subordinate im- 

 portance, inasmuch as they chiefly represent 

 reserves of material to be drawn on at periods 

 when the nucleus is undergoing division. The 

 more solid gelatinous matrix (linin) contains 

 the most important nuclear constituents. -A 

 more or less finely divided substance distri- 

 buted in the gelatinous matrix often gives the 

 nucleus a rather granular appearance. Stains 

 of various kinds render this much more 

 evident, and the stainable particles are often 

 known as chromatin. 



When the nucleus is about to divide, strik- 

 ing rearrangements are observed to take place 

 within it. The gelatinous linin, in which the 

 chromatin is diffused, contracts, and at the 



