30 



PHYSIOLOGY 



we have, in the case of the nerve-cell, an example of the necessity of the 

 nucleus for growth. Here division of the nerve fibre causes degeneration of 

 the whole fibre separated from the cell containing the nucleus, and regenera- 

 tion of the fibre, when it occurs, is effected by a down-growth of that part of 

 the fibre which is still in connection with the nucleus. All these facts show 



A 



D 



FIG. 10. Formation of membranes by protoplasmic fragments of plasmolysed cells. 



( WILSON after TOWNSEND.) 



A. Plasmolysed cell, leaf -hair of Cucurbita, showing protoplasmic balls connected 

 by strands. B, Calyx-hair of Oaillardia ; nucleated fragment with membrane, non- 

 nucleated one naked. C. Root-hair of Marchantia ; all the fragments, connected by 

 protoplasmic strands, have formed membranes. Z>. Leaf-hair of Cucurbita ; non- 

 nucleated fragment, with membrane, connected with nucleated fragment of adjoining 

 cell. 



that the power of morphological as well as of chemical synthesis depends on 

 the presence of a nucleus. On this account the nucleus, as we shall learn 

 later on, must be regarded as the especial organ of inheritance. The trans- 

 mission of the paternal qualities from one generation to the next is effected by 

 the entrance simply of the nuclear material of the male cell, the spermatozoon, 

 into the ovum. In the words of Claude Bernard, " the functional phenomena 

 in which there is expenditure of energy have their seat in the protoplasm of 

 the cell (i.e. the cytoplasm). The nucleus is an apparatus for organic syn- 

 thesis, an instrument of production, the germ of the cell." 



Similar conclusions may be drawn from a study of the changes in the 

 nucleus which accompany different phases in the activity of the whole cell. 



