366 THE HISTORY AND SCOPE OF ZOOLOGY IX 



for one of the chemical substances of which Schultze's 

 protoplasm is a structural mixture — namely, that 

 highest point in the chemical elaboration of the mole- 

 cule which is attained within the protoplasm, and up 

 to which some of the chemical bodies present are 

 tending, whilst others are degradation products result- 

 ing from a downward metamorphosis of portions of it. 

 This intangible, unstable, all-pervading element of 

 the protoplasm cannot at present be identified with 

 any visibly separable part of the cell-substance, which 

 consists of a hyaline denser network of excessive 

 tenuity, of a less dense hyaline liquid, and of finest 

 and less fine granules of varying chemical nature. 

 This "critical" substance, sometimes called "true 

 protoplasm," should assuredly be recognised by a dis- 

 tinct name "plasmogen," Avhilst protoplasm retains 

 its structural connotation. 



The study of the process of fertilisation and of the 

 significance in that process of the distinct parts of 

 the sperm-cell and egg-cell — the separate fibrillae and 

 granules of the nuclei of those cells — at the present 

 moment forms one of the engrossing subjects of zoo- 

 logical investigation.^ Not less important is the 

 descent, as it were, of physiological investigation in 

 relation to every organ into the arena of the cell : 

 digestion, secretion, muscular contraction, nerve action, 

 all are now questions of Plasmology, or the study of 

 cell-substance founded by Schwann. 



^ See tlie memoirs of Weismann on Heredity and F. M. Balfour's 

 Embryolorjij. 



