192 PROCEEDIXGS OF THE ACADEMY OF [April, 



correct to build upon classifications which would neglect many of 

 the energies and phenomena of organisms which particularly dis- 

 tinguish them from non -organisms. 



There then remain to be compared the morphological, physiological, 

 ecological and psychical classifications, and to be determined which 

 of them can be most profitably employed in tracing the course of 

 evolution. All these are closely related, for the nervous system, 

 e. g., shows a structure, a function, a relation to habits and envi- 

 ronment, and to so-called mental phenomena. The living structui e 

 and its activity are inseparable, and both have close connection with 

 the envii'onment. The fact that they are all so closely and insepar- 

 ably correlated that in treating of an organism the naturalist is 

 obliged to regard it in all of these aspects, would argue that a 

 classification might be based equally well upon any one of them. 

 Much more has been determined in regard to structural than to 

 physiological, psychical or ecological relations of organisms, so that 

 a morphological, classification, having more facts at its command, 

 is at present more practicable than any other. In time the mor- 

 phological classification must be tested by the others, and now no 

 phyletic classification is justifiable which wotild not regard the 

 functions and the interactions to the environment, for these have 

 modified the structure. Function has produced structure, and 

 structure so formed in turn tends to restrain change of function, 

 and the stimuli of the environment are the strong masters of the 

 organism. Hence structure, function, relation to environment, 

 each mirrors the others, any one of them might be the basis of 

 the classification ; and if we now select the morphological charac- 

 teristics as the basis for determining the phylogcny, it is because 

 they offer us at present the richest material. But starting as we do 

 with a classification based upon similarities determined on structure, 

 we are not to consider that on structure alone our ultimate phylelic 

 classification is to rest; for to understand the phylogeny of organ- 

 isms we should not view them as seen in certain instants of time 

 only, but must explain the continuous change that has occurred 

 between those instants by analyzing the phenomena of growth and 

 of reaction to en^^ronmental stimuli. The phenomena of structure, 

 when the comparisons have been rightly instituted, may go far 

 toward explaining the path of evolution, but the change produced 

 l^y evolution, wliich is equally necessary for our ideas of phylo- 



