586 



SCIENCE 



[Vol. LVI, No. 1456 



least so far as zoology was concerned, was a 

 curious one. It led to an enormous develop- 

 ment of research in what is perhaps the most 

 essentially static branch of biology, namely, 

 pure morphology. The process of reasoning 

 was something like this. Since evolution leaves 

 a record of its progress in the structures of ani- 

 mals, by studying these stmctui-es intensively 

 it ought to be possible to reconstruct not only 

 the course, but even also the method, of evolu- 

 tion. Von Baer's so-called law, to the effect 

 that ontogeny repeats phylogeny, was held to 

 be the key that would unlook all the secret 

 places of organic evolution, and the biological 

 world went more or less mad over embryology. 



But as has already been pointed out, this 

 line of attack proved to be sterile, so far as the 

 problem of evolution is concerned. Ontogeny 

 does not repeat phylogeny with anything like 

 that degree of fidelity which would be required 

 if it were to be the means of unravelling the 

 tangled thread of evolutionary progress. And 

 the observed static end results given by the 

 structures of existing animals are capable of 

 being produced in too many different ways, as 

 we now know, to mate possible any precise con- 

 clusions from the mere study of their form as 

 to the dynamic course of events which led to 

 their existence. 



IV 



When this fact had become evident and sunk 

 •deeply into the consciousness of the working 

 biologists, the way was cleared for the begin- 

 ning of the great movement towards modern 

 general biology. It is an odd mischance of fate 

 that Darwin, who is the real founder of modern 

 ^general biology, should not have seen any of its 

 fruits in the declining years of his life, but in- 

 stead only an abortive development resting on a 

 ridiculously unsound philosophy. When bi- 

 ology, at the very end of the nineteenth cen- 

 tury, got once more on the right track (for 

 much earlier in its history it had been 

 there, and only got diverted by a bad 

 philosophy as to how the problems of 

 •evolution could be solved) a new world was 

 indeed opened to our vision. And the pass- 

 word to it was experimentation. To the work- 

 ing biologist organisms once more became living 



things, not desiccated or pickled corpses. I 

 cannot recall that in my undergraduate days 

 there ever was a living animal in the labora- 

 tory, with the exception of protozoa. Cer- 

 tainly none was ever studied in any but a 

 thoroughly pickled condition. As one looks 

 back now ou those days he is horrified not alone 

 at the tortuosity of the intellectual pathway by 

 which we attempted to come upon a knowledge 

 of life, but also at the awful waste of alcohol! 



The keynote of the new biology was dynamic 

 and its methods were, in the main, experimen- 

 tal. Each of the old disciplines took on a new 

 life. Morphology 'became experimental mor- 

 phology; evolution became experimental evolu- 

 tion; a new shoot, ecology, sprang up from the 

 gnarled old root of the taxonomic tree; and in 

 some sense as the crowning glory of the whole 

 edifice, animal behavior and comparative psy- 

 chology began to flourish and attain a respecta- 

 bility never enjoyed 'by the labors of the old- 

 fashioned naturalist, who observed what he 

 called the "habits" of animals and plants. 



Since these movements I have named com- 

 prise nearly the whole of the major trends of 

 biology in the twentieth century it will perhaps 

 be worth our while to examine a little more 

 carefully into the philosophy and significance 

 of each of them. For on and out of them is to 

 grow the biology of the future, with all the 

 great advances in knowledge which it has in 

 store. 



"V 



Modern experimental morphology may fairly 

 be said to begin with Rous. His philosophy 

 may be sunmiarized in this way : organisms are 

 machines which in their operations follow the 

 laws of mechanics. Their structures are as 

 they are because of the operation of these laws 

 upon the plastic and adaptable material of 

 which they are composed. It is the task of ■de- 

 velopmental mechanics to discover the specific 

 physical and chemical laws which determine 

 the form of particular structures of the living 

 body. On the whole the most feasible way to 

 go aboiit accomplishing this result is to ob- 

 serve the results which follow upon the experi- 

 mental modification of the physical and chemi- 

 cal conditions which en\dron the embryonic de- 



