THE CELL AND PROTOPLASM. 109 



cell substance, and it goes through a series 

 of activities which are entirely unrepresented 

 in the surrounding protoplasm. It is some- 

 thing entirely distinct, and its relations to the 

 life of the cell are unique and marvellous. 

 These various facts led to a period in the dis- 

 cussion of biological topics which may not in- 

 appropriately be called the Reign of the Nucleus. 

 Let us, therefore, see what this structure is 

 which has demanded so much attention in the 

 last twenty years. 



(b) Structure of the Nucleus. At first the 

 nucleus appears to be very much like the cell 

 substance. Like the latter, it is made of fibres, 

 which form a reticulum (Fig. 23), and these 

 fibres, like those of protoplasm, have micro- 

 somes in intimate relation with them and hold 

 a clear liquid in their meshes. The meshes of 

 the network are usually rather closer than in 

 the outer cell substance, but their general 

 character appears to be the same. But a more 

 close study of the nucleus discloses vast differ- 

 ences. In the first place, the nucleus is usually 

 separated from the cell substance by a membrane 

 (Fig. 23, c). This membrane is almost always 

 present, but it may disappear, and usually does 

 disappear, when the nucleus begins to divide. 

 Within the nucleus we find commonly one or two 

 smaller bodies, the nucleoli (Fig. 23, /). They 

 appear to be distinct vital parts of the nucleus, 

 and thus different from certain other solid bodies 

 which are simply excreted material, and hence 

 lifeless. Further, we find that the reticulum 

 within the nucleus is made up of two very differ- 



