1 8 PROTOPLASMIC ACTION AND NERVOUS ACTION 



as the all-essential ones. To do so would be to imply 

 that in the early or precellular stages of organic evolution 

 the assimilative or proliferative types of colloidal 

 material, which presumably were then the only systems 

 representing organisms, were not living. The formation 

 of a particular kind of structure is not the essential 

 criterion of vitality; the properties which underlie the 

 formative or structure-building activities are the primary 

 ones. In most animals and plants these activities give 

 rise to a cellular type of structure, but this is not neces- 

 sarily true of all. 



IMPORTANCE OF CELLULAR ORGANIZATION 



There is a sense, therefore, in which we may regard 

 the cellular type of structural organization as not so 

 much the cause or necessary condition of the vital 

 activities as their product or effect. Obviously all 

 cellular organisms come into existence through the 

 constructive processes of growth. This was pointed out 

 by Huxley, in the early years of the cell theory, in a 

 well-known passage in which he speaks of the cells as 

 being not the producers but simply the products or 

 indicators of vital action. Like the shells on the. sea 

 beach the cells "mark only where the vital tides have 

 been and how they have acted."' This comparison is 

 an apt one in that it emphasizes the primary importance 

 of the structure-forming vital activity which expresses 

 itself in the formation of cells; but it tends perhaps to 

 subordinate the part played by the cellular structure, 

 once it has been attained. There is no doubt that this 



^ Cf. Huxley, "Review of the Cell Theory" in the British and Foreign 

 Medico-chiriirgical Review (1853), 



