BEHAVIOR OF VERTEBRATES 413 



to the raccoons and to the child in his monograph on the delayed 

 reaction was the residual effect of sensory stimuli, strictly sensory 

 in content. Quite in a line with the above question are the ex- 

 periments of Walton (35) who undertook to determine what 

 would be the effect of diverting stimuli during delayed reaction 

 with dogs. In the main there was an attempt to follow Hunter's 

 methods and type of apparatus, i. e., the dogs were confined in 

 a release box from which it was possible to see four compartments 

 twelve feet distant. The animals were to choose the compart- 

 ment after the light which indicated it had been turned off from 

 one second to five minutes. After the reaction was learned and 

 during this delay, visual, olfactory and auditory distractions 

 were used. The experimenter differs from Hunter in conclud- 

 ing that though signs of orientation may be prominent in the dog 

 such clues are not important for the success of the reaction in 

 the animals used. It cannot too frequently be urged that in 

 order to duplicate results apparatus and methods should be 

 identical. It should also be reiterated that there is little doubt, 

 at least with dogs, that no safe conclusions can be drawn as to 

 cues when the operators are visible. They should preferably 

 be out of the room. The method and the type of apparatus 

 which had been used in the study of the dancing mouse were 

 this year applied by Dodson (9) to his study of the relation of* 

 the strength of the stimulus to the rapidity of habit formation. 

 By stimulus is meant here not the strength of the light to 

 which the kittens were reacting but the strength of the punish- 

 ment by the electric grill when they failed to choose rightly. 

 The kittens of which there were eighteen were required to choose 

 correctly between light and dark boxes and each cat was given 

 ten trials per day until it had chosen correctly for three successive 

 days. The difference in brightness to be discriminated in one 

 series was very great, in another medium, and in another very 

 slight. The experimenter thinks that the relation of the pain- 

 fulness of the electrical stimulus to the rapidity of habit forma- 

 tion depends upon the difficulty of the visual discrimination. 

 Hubbert (11) using albino rats studied the effect of age on habit 

 formation. The apparatus concerned in the experimentation 

 was Watson's circular maze with camera lucida attachment. 

 Five groups of rats aged 25, 65, 200, 300 and 500 days, took part 

 in the experiments. These groups numbered 27 and 28 animals 



