64 G. V. HAMILTON 



The ontogenetic findings parallel the phylogenetic ; among 

 human subjects, monkeys, dogs of three different age-groups, 

 and cats, there is apparent a tendency for a sufficient decrease 

 in age to decrease the percentage of Type B reactions 



(3) The tendency to adopt stereotyped modes of searching (Type 

 C) seems to acquire its maximum phylogenetic value for the 

 monkeys ; it is but slightly apparent in the behavior of the older 

 normal human subjects and the other mature animals. 



The ontogenetic relationships of this reactive tendency are 

 interesting. The immature monkeys and defective Boy A 

 are especially affected by it; but it is more apparent in the be- 

 havior of the older puppies than in that of either the mature 

 dogs or the younger puppies. The latter circumstance is a 

 matter of some perplexity to the writer, since, as has been said, 

 the Type C reaction becomes an habitual mode of adjustment 

 with mature dogs who have had sufficiently prolonged expe- 

 rience with the situations of the experiment. 



(4) The searching tendency modified by recrudescent motor 

 impulses (Type D reaction) regularly increases in frequency of 

 manifestation as we descend the phyletic scale of mature sub- 

 jects until we reach the mature dogs, at which point it attains 

 its maximum frequency. This tendency decreases as we pass 

 further down the scale through the cats to the horse. 



Ontogenetically, it increases in frequency of manifestation 

 with descent from older childhood to infancy; but, with one 

 exception, the younger animals are less affected by it than are 

 their older fellows ; the younger puppies give a higher percentage 

 of the Type D reactions than do the older puppies. 



(5) The tendency toward perseveration of active motor im- 

 pulses and of inhibitions (Type E) increases regularly in the 

 frequency of its manifestation as both the ontogenetic and 

 phylogenetic scales are descended. It is of interest that during 

 the total one thousand trials of the ten older human subjects 

 (the two defectives being included) there was but one manifes- 

 tation of this tendency — the first reaction of the much embar- 

 rassed Boy 7, whilst 34.21 per cent of the infant's classified 

 reactions may be ascribed to this tendency. 



The present investigation has afforded experimental evidence 

 that the phylogenetic and ontogenetic differences of adequacy 

 of mammalian adjustments are to be accounted for not merely 



