THE FACTORS OF ORGANIC EVOLUTION. 



103 



those named above is practically to make impossible at 

 present any explanation of vital phenomena. " If we 

 would advance without interruption," says Roux,* " we 

 must be content, for many years to come, with an analy- 

 sis into complex components." 



2. We need not now further concern ourselves with 



an explanation of extrinsic causes or simple components, 



since this subject properly belongs to 



Intrinsic causes chemistry and physics. If, however, we 

 arise from nature . , , ... 



r . , examme more closely some of the in- 



of protoplasm. _ _ •' 



trinsic causes or complex components, we 

 will find that they are always associated with more or 

 less complex structures ; in fact, they are depe7ident upon 

 structure. 



The smallest and simplest mass of protoplasm that 

 can manifest all the fundamental phenomena of life, 

 such as assimilation, growth, division, and metabolism, 

 is an entire cell, nucleus and cytoplasm, and probably 

 centrosome. The cell is composed, as microscopic study 

 plainly reveals, of many dissimilar but perfectly co- 

 adapted parts, each performing its specific function, and 

 it may therefore properly be called an organism. Some 

 phenomena of cell life may be directly referred to 

 the various visible constituents of the cell, but many of 

 them are evidently connected with structures which we 

 can not see, structures which may perhaps never be 

 seen, and yet which must be vastly more complex than 

 the most complex molecules known to chemistry, and 

 yet much more simple than the microsomes, centro- 

 somes, and chromosomes which are visible in the cell. 

 With these ultra-microscopical particles many of the 

 most fundamental phenomena of life are associated — 

 viz., assimilation, growth, metabolism, and probably 



*Wilhelm Roux. Einleitung : Archiv fiir Entwickelungsmecha- 

 nik der Organism, 



