14 



GENERAL SKETCH OE THE CELL 



smaller body, the nucleolus. Thus the cell came to be defined by 

 Max Schultze and Leydig as a mass of protoplasm containing 

 a nucleus, a morphological definition which remains sufficiently satis- 

 factory even at the present day. Nothing could be less appropriate 

 than to call such a body a " cell " ; yet the word has become so firmly 

 established that every effort to replace it by a better has failed, and 

 it probably must be accepted as part of the established nomenclature 

 of science.^ 



Attraction-sphere enclosing two centrosomes. 



I Plasmosnme or 

 true nucleolus. 



Chromatin- 



network. 



Nucleus -i 



Linin-network. 



Karyosome or 

 net-knot. 







Plastids lying in the 

 cytoplasm. 



Vacuole. 



Lifeless bodies (meta- 

 plasm) suspended in 

 the cytoplasmic reticu- 

 lum. 



Fig. 5. — Diagram of a cell. Its basis consists of a thread-work (viitome, or teticuluiii) com- 

 posed of minute granules (//uc/oso/?ies) and traversing a transparent ground-substance. 



A. General Morphology of the Cell 



The cell is a rounded mass of protoplasm which in its simplest 

 form is approximately spherical. This form is, however, seldom 

 realized save in isolated cells such as the unicellular plants and 

 animals or the egg-cells of the higher forms. In vastly the greater 

 number of cases the typical spherical form is modified by unequal 

 growth and differentiation, by active movements of the cell-substance, 

 or by the mechanical pressure of surrounding structures. The 



1 Sachs has proposed the convenient word energid (^Elora, '92, p. 57) to designate the 

 essential living i)art of the cell, i.e. the nucleus with that portion of the active cytoplasm 

 that falls within its sphere of influence, the two forming an organic unit both in a morpho- 

 logical and in a physiological sense. It is to be regretted that this convenient and appro- 

 jiriale term has not come into general use. (See also Elora, '95, p. 405.) 



