Animal Psychology, the Old and the New 33 



ways in adaptation to changed conditions of life. 



The behavior not only of the Protozoa but of all 

 higher classes of animals has been studied in the 

 last few years with a great increase of zeal - and 

 thoroughness. The activities of hydroids, jelly-fish, 

 worms, mollusks, echinoderms, crustaceans, as well 

 as insects, and vertebrates, have engaged the atten- 

 tion of a small army of investigators who are 

 rapidly amassing a vast store of detailed knowledge. 

 A very few years ago there was established a spe- 

 cial periodical, The Journal of Animal Behavior, 

 devoted exclusively to papers on animal psychology, 

 while an increasing amount of literature on the sub- 

 ject is going into other channels. 



The days of anecdotal psychology, when it was 

 the fashion to bring together stories from various 

 sources illustrative of animal sagacity, are passing. 

 The psychological interpretation of animal behavior 

 is a subject that abounds in pitfalls for the un- 

 wary. To find out what probably goes on in an 

 animal's mind requires close and continuous obser- 

 vation, and usually experiments under carefully con- 

 trolled conditions. The careful experimental work 

 of Thorndike, Cole, Yerkes, Hobhouse, Small and 

 many other investigators, has given us a more ex- 

 act knowledge of the mental activities of the ani- 

 mals studied than would have been possible through 

 the collection of any quantity of scattered observa- 

 tions. The results have sometimes proven disap- 

 pointing to zealous champions of the high mental 



