PSYCHOLOGY: R. M. YERKES 
633 
of certain acquired motor tendencies, one of which may be described 
thus. The rat follows the wall of the reaction compartment to the 
entrance to the box at the right end of the series of boxes. It then 
turns sharply to the left and passes along close to the boxes until the 
first open door is reached. This it enters. Kinaesthetic, tactual, and 
\'isual data constitute the basis for the motor habits by which rats 
solve this simple relational problem. 
A single individual exhibited reactive tendencies less obviously de- 
scribable in motor terms, but it is by no means certain that this indi- 
cates ideational ability sufficient for the solution of relational problems. 
Problem 2 was not solved by rats within 800 trials, and there is no 
indication in the data that solution is possible to them. 
Whereas the influence of training in problem 1 disappeared quickly 
when problem 2 was presented to the crow, it persisted in the case of 
the rat for about 100 trials. There are numerous other evidences, in 
the experimental data, of the higher intelligence of the crow. The rat 
is distinctly less versatile and markedly less responsive to slight changes 
in environment. 
(3) Pigs solve problem 1 with 50 trials or less; problem 2 with 390 
to 600 trials; problem 3 with 420 to 470 trials. Problem 4 is not solved 
in 800 trials. 
These successes as well as the varied reactive tendencies manifested 
place the pig much higher in the scale of adaptive capacity than the 
rat or crow. 
The data obtained with these three types of subject proves the 
method of multiple choices to be a feasible means of eliciting reactive 
tendencies which are characteristic of various points in ontogeny and 
phylogeny. 
Results which have been obtained with monkeys, apes, and men will 
be presented in separate communications. 
^ Yerkes, Robert M., The study of human behavior, Science, 39, 625-633 (1914). 
Cobum, Charles A. and Yerkes, Robert M., A study of the behavior of the crow, Corvus 
Americanus Aud., by the multiple-choice method, /. Animal Behavior, 5, 75-114 (1915). 
Yerkes, Robert M. and Coburn, Charles A., A study of the behavior of the pig, Sus 
scrofa, by the multiple-choice method. /. Animal Behavior, 5, 185-225 (1915). 
Burtt, Harold E., A study of the behavior of the white rat by the multiple-choice method, 
/. Animal Behavior, 6, 222-246 (1916). 
Yerkes, Robert M,, The mental life of monkeys and apes: a study of ideational be- 
havior, Behavior Monographs, 3, Serial number 12 (1916). 
^Thomdike, E. L., Animal Intelligence, New York, 1911. 
'Hamilton, G. V., A study of trial and error reactions in mammals,/. Animal Behavior, 
1,33 (1911). 
^Hunter, W. S., The delayed reaction in animals and children, Behavior Monographs, 
2, serial number 6 (1913). 
