10 



reproduction in the organism. Our present concern being 

 with the microscopic features of the nucleus, its detailed 

 structure will now be considered. 



STRUCTURAL FEATURES. 

 The nucleus, typically spherical, may take a form 

 corresponding somewhat to the contour of the cell, 

 elliptically or otherwise lengthened in elongated cells, &c., 

 or may even show amoeboid characters (Fig. 4). Its 

 position is usually central in egg and other reproductive 

 cells, also in young tissue cells, as well as in those of mid- 

 life, being maintained in position by connecting proto- 

 plasmic threads. Finally, in mature cells it lies alongside 

 the cell wall imbedded in the lining layer of cytoplasm. 



THE NUCLEOPLASM. 

 The basis of nuclear construction is a fine network of 

 nucleoplasm termed linin, like the meshwork found in the 

 cytoplasm of the cell, and from which it is said to differ 

 but slightly, either in chemical or staining properties. Some 

 investigators believe them to consist of the same material, 

 and have found evidence of their connection by means of 

 filaments that pass from both into the nuclear membrane.^ 

 And when the membrane disappears, as during the course 

 of nuclear division, the nucleoplasm and cytoplasm are 

 brought into direct contact (Fig. 17). At the close of the 

 division the cytoplasm of each daughter cell undoubtedl)- 

 receives a portion of the dispersed nucleoplasm shut out 

 from their nuclei, and this, as some have pointed out, may 

 have a bearing upon the question of inheritance by the 

 cytoplasm.5 



In well-fixed and typically-stained preparations the 

 nuclear reticulum is seen to consist of linin filaments 

 studded with minute granules, microsomes, the intervening 



