1912^ Zoology in America 67 



along the lines laid down hj the great French zoologist, Lam- 

 arck, and assume that the changes induced in an individual by 

 habit and by the direct action of the environment are inherited. 

 Little, even today, is known on this head, and however suggestive 

 and valuable such theories are, it would seem that nothing cer- 

 tain can be learned from comparison alone. Darwin's theory 

 of natural selection, of the selective influence of the environ- 

 ment, helps us to understand one great, universal attribute of 

 organisms, viz., that structure in general is useful, is adaptive, 

 and again why the descendents of a species should tend to split 

 up into divergent races. But as to the underlying physiolog- 

 ical processes concerned in the production of the initial differ- 

 ences between individuals, on which selection operates, it tells 

 us nothing. Nor does it give us information which would enable 

 us even to pick out with certainty the kinds of initial differences 

 on which selection can ojjerate. Lamarck, Darwin, and evolu- 

 tionists in general have all along seen clearly that such prob- 

 lems can only be answered with the aid of experiment. 



This word, "^experiment," is the master-word to the under- 

 standing of the present era in zoology, but with the oncome of 

 this era my sketch must come to an end. Wherever we look 

 today, whether to studies revolving round the idea of species, 

 or to those dealing with habit, or with anatomy, or with the tis- 

 sues, or with the cell, everywhere we find that along with obser- 

 vation and comparison, experiment has entered in. In some 

 fields the new method is easy to practise and is dominant, in 

 others it is difficult and therefore only accessory. With the 

 introduction of experiment it would seem that many questions 

 which have been raised should find an answer. Certainly the 

 outlook is hopeful. 



Chapel Hill, N. C. 



