OF THE CELL THEORY 173 



of the nucleus, and the free ends of the threads 

 interlacing at the other pole. The secondary 

 threads form a fine network, connecting together 

 the primary threads, and may be so numerous as 

 to conceal more or less completely the definite 

 arrangement of these latter. The nucleoli are 

 spherical bodies of various size, which stain deeply 

 with the ordinary colouring reagents. It is not 

 certain whether they are in all cases corresponding 

 structures. Sometimes they are merely nodes or 

 local thickenings of the network of threads, while 

 at other times they appear to be quite independent 

 of the network. The general tendency at present 

 is to regard them as non-essential, or at any rate 

 secondary structures ; and it is held by many that 

 their purpose is to serve as a store of reserve 

 matter for the nutrition of the other constituents of 

 the nucleus. 



The nuclear membrane has recently attracted 

 renewed attention. By many it is regarded merely 

 as a denser and superficial part of the nuclear 

 reticulum ; while by others it is held that it is, 

 at any rate in certain cases, a continuous mem- 

 brane, though authorities are not agreed as to 

 whether it belongs really to the nucleus itself, or 

 is rather to be regarded as a limiting layer of 

 the cell protoplasm, immediately surrounding the 

 nucleus. 



The nucleoplasm or nuclear sap, which fills up 

 the whole of the rest of the nucleus, is an 

 albuminous coagulable liquid. A fine reticulum has 

 been described in some cases as traversing the 



