14 president's address. 



What 1 claim is that, as regards reaction to environment, a plant and 

 a man must be placed in the same great class, in spite of the obvious 

 fact that as regards complexity of behaviour the difference between them 

 is enormous. I am not a psychologist, and I am not bound to give an 

 opinion as to how far the occurrence of definite actions in response to 

 stimulus is a physiological and how far a psychological problem. I am 

 told that I have no right to assume the neural series of changes to be the 

 cause of the psychological series, though I am allowed to say that neural 

 changes are the universal concomitants of psychological change. This 

 seems to me, in my ignorance, an unsatisfactory position. I find myself 

 obliged to believe that the mnemic quality in all living things (which 

 is proved to exist by direct experiment) must depend on the physical 

 changes in protoplasm, and that it is therefore permissible to use these 

 changes as a notation in which the phenomena of habit may be expressed. 



Habit illustrated by Mor2)hology. 



We have hitherto been considering the mnemic quality of movements ; 

 but, as I have attempted to show, morphological changes are reactions to 

 stimulation of the same kind as these temporary changes. It is indeed 

 from the morphological reactions of living things that the most striking 

 cases of habit are, in my opinion, to be found. 



The development of the individual from the germ-cell takes place by a 

 series of stages of cell-division and growth, each stage apparently serving 

 as a stimulus to the next, each unit following its predecessor like the 

 movements linked together in an habitual action performed by an animal. 



My view is that the rhythm of ontogeny is actually and literally a 

 habit. It undoubtedly has the feature which I have described as pre- 

 eminently characteristic of habit, viz., an automatic quality which ia 

 seen in the performance of a series of actions in the absence of the com- 

 plete series of stimuli to which they (the stages of ontogeny) were originally 

 due. This is the chief point on which I wish to insist — I mean that the 

 resemblance between ontogeny and habit is not merely superficial, but 

 deeply seated. It was with this conclusion in view that I dwelt, at 

 the risk of being tedious, on the fact that memory has its place in the 

 morphological as well as in the temporary reactions of living things. 

 It cannot be denied that the ontogenetic rhythm has the two qualities 

 observable in habit — namely, a certain degree of fixity or automaticity, 

 and also a certain variability. A habit is not irrevocably fixed, but may 

 be altered in various ways. Parts of it may be forgotten or new links 

 may be added to it. In ontogeny the fixity is especially observable in 

 the earlier, the variability in the later, stages. Mr. Darwin has pointed 

 out that ' on the view that species are only strongly marked and fixed 

 varieties, we might expect often to find them still continuing to vary in 

 those parts of their structure which have varied within a moderately 

 recent period,' These remarks are in explanation of the ' notorious ' fact 



