5 oz 



THE QUARTERLY REVIEW OF BIOLOGY 



that the development of refined experi- 

 mental methods affords a good index of 

 the growing maturity of a science, indi- 

 cating an increasing ability to adequately 

 define and solve its problems. 



The decade centering around 1900, as 

 stated above, witnessed a most remarkable 

 outburst of experimental work of a highly 

 original order in many fields. It will be 

 convenient, in tracing out the more 

 important lines of progress, to begin with 

 the work on lower forms and follow 

 systematically through to the higher. In 

 addition to outlining the major events of 

 the decade under review, attention will be 

 called, from time to time, to a few of the 

 more outstanding later developments. 



The interest aroused in the sensitivity of 

 plants by the theory and work of Darwin 

 led to continued experimentation among 

 the botanists (47, 53). Nemec, Haber- 

 landt, Ricca, and later Fitting may be 

 named among the more prominent investi- 

 gators of tropistic behavior. In the field 

 of genetics and evolution, De Vries, 

 Bateson and others made notable contribu- 

 tions. 



The interest in the behavior of lower 

 organisms aroused by the work of Ver- 

 worn and Loeb proved to be permanent. 

 Loeb in particular continued to the last 

 his experimental investigations and many 

 of his students were inspired to enter the 

 field and attempt to solve the problems of 

 behavior by the physiological approach. 

 The work of Jennings (149), which began 

 to appear about 1897, gave a new impetus 

 to the study of the lower organisms. 

 Jennings — who had studied at Jena under 

 Verworn — may be thought of as continu- 

 ing the tradition of Engelmann and Ver- 

 worn in contradistinction to that of Loeb. 

 Like both of these earlier workers he was 

 impressed by the variability of behavior 

 even in such simple forms as the protozoa 

 and emphasized, as Verworn had done, 



the internal factors in response. Jennings 

 held that the characteristic behavior of 

 lower forms is less simple than Loeb's 

 tropism theory would seem to require; 

 that their responses are typically variable 

 to the same stimulus as their physiological 

 states vary from time to time and from 

 individual to individual; that instead of 

 being direct and forced in Loeb's sense 

 their responses are usually of the "trial 

 and error" type, which favors modifi- 

 ability. The opposing views of Loeb and 

 Jennings may be partially explained by the 

 fact that the former worked for the most 

 part on sessile, or relatively inactive 

 forms, whereas the latter studied mainly 

 the more active, free-swimming types. 

 As thus viewed, their work both theo- 

 retical and experimental appears to be 

 complementary rather than antagonistic. 

 Among other early workers on lower 

 organisms, Parker, Holmes, Yerkes, and 

 Mast in America; Bethe and von Uexkiill 

 in Germany, and Pieron and Bohn in 

 France deserve special mention. Parker's 

 study on the behavior of Metridinm 

 appeared in 1896, and each of the other 

 investigators began their work on lower 

 organisms either before, or soon after 1900. 

 A few scattered applications of experi- 

 mental methods to the study of the 

 behavior of the arthropoda took place 

 during the decade. Following the rather 

 casual test of learning ability in the crab 

 by Bethe (1897), Yerkes adapted the maze 

 method to this form in 190Z, and extended 

 it to the crayfish the following year. A 

 further study of learning ability in the 

 crab was made by Spaulding in 1904. The 

 bulk of work on insects and other air- 

 breathing arthropoda continued to be 

 either field observations or semi-experi- 

 mental investigations of sensory capac- 

 ities and intelligence. Such careful 

 workers as Wasmann, Forel, Claparede, 

 and the Peckhams continuing from the 



