observers, quickly demonstrated that the nucleus was a 

 normal organ in both plant and animal cells — at least, all 

 in a young state. It was supposed to originate within, and 

 from the viscid plasmic cell contents, named protoplasm by 

 Von Mohl in 1 846. The protoplasm, in the form of a very 

 fine network enclosing cell sap between the meshes, is now 

 distinctively known as cytoplasm, which term also 

 distinguishes it from the similar network of nucleoplasm 

 (linin) in the nucleus. Out of the cytoplasm first arose 

 the nucleolus, a minute more or less spherical body, around 

 which the nucleoplasm was " precipitated," somewhat as 

 crystals might be from a mother-lye, the outer portion 

 consolidating into the nuclear membrane, and this in turn 

 was surrounded by the protoplasm of the cell. Closer 

 observations failed to show that any such apparent 

 spontaneous formation of nuclei ever took place, rather 

 the reverse, that every nucleus was derived from a parent 

 nucleus, hence the formula omnis nucleus e nucleo became 

 established. This was later extended to cover the fact 

 that in all plants with normal sexual reproduction every 

 nucleus produced during the ontogeny or development of 

 the individual is primarily descended from the nucleus of 

 the fertilised e^gg, i.e., a nucleus formed by the union of egg 

 and sperm nuclei. Attempts to further apply this dictum 

 to the origin of the nucleolus have so far not been 

 successful, its functions are still imperfectly understood 

 and the subject of various interpretations.^ 



Concentration of research upon the nucleus brought 

 into relief its composite nature and complex construction ; 

 its physical characters and varying chemical composition at 

 different stages of its history. With improved instruments 

 and methods of fixing and staining material, the parts 

 played by the nucleus are seen to be of the first 

 importance in every aspect of development, nutrition and 



