November 24, 1922] 



SCIENCE 



587 



velopment of particular structures. Then in 

 the favorable ease we shall be able definitely 

 to connect and correlate particular physico- 

 chemical events with particular biological 

 evenits in a causal way. We shall replace 

 metaphysical speculation in the field of mor- 

 phology with observed physical causation. 



The results of the last quarter century have 

 abundantly justified the faith of Rous and his 

 followers in soundness of this philosophy. So 

 «lose are we to the events themselves, however, 

 that we cannot justly appreciate, I helieve, the 

 enormous significance of the advance in our 

 knowledge of the fundamentals of biology 

 which have come as the result of the labors in 

 this field of a host of workers, under the leader- 

 ship of Rous in Germany and of Morgan in 

 this country. The important advances in this 

 field have, in the main, come from these two 

 countries. 



The great activity in the fields of experi- 

 mental morphology and developmental me- 

 chanics has also been in considerable degree re- 

 sponsible for the growth and healthy condition 

 of another major trend in modern 'biology, 

 namely cytology. This is pure morphology at 

 its best, resting on the sound philosophical pur- 

 pose of the exact description of the minute 

 anatomy of the cell. In this field America has 

 again heen a leader. E. B. Wilson's book,' 'The 

 Cell in Development and Inheritance," may 

 well be said to mark an epoch, at least in Am- 

 erican biology. The achievements of cytology 

 in the last quarter century have been of no 

 mean importance. This field of research, for 

 example, has played the leading role in clearing 

 up the age old problem of the determination of 

 sex. The discovery by McClung of a mechan- 

 ism in the germ cells, the accessory or sex 

 chromosomes, and the subsequent great exten- 

 sion and solid grounding of this knowledge by 

 Wilson and his students, have served to take 

 out of the realm of mysticism and put into the 

 clear light of ascertained fact the answer to 

 one of the great biological riddles. Again, in 

 this same period eytologieal research has laid 

 the sti-uctural foundation of the mechanism of 

 heredity. The student of the history of science 

 will note here an interesting fact. Discoveries 



of major importance in regard to dynamic bio- 

 logical events have here been made ;by a purely 

 static, descriptive mode of research. This is 

 unusual. Why it has happened so fortunately 

 is because the American workers in cytology, 

 in the period of which we are speaking, have 

 at every stage worked in the closest touch vsith 

 the experimentalists, and have directed theii' 

 descriptive studies to problems which have 

 made themselves compeUingly obvious from and 

 in the experimental work which was going on 

 at the same time, and in many cases in the same 

 laboratory. A static method has worked in cor- 

 relation and cooperation with a dynamic experi- 

 mental method. We see beautifully exemplified 

 here one of the main functions of descriptive 

 science in general, in relation to experimental 

 science. The descriptive worker endeavors to 

 lay the structural foundation of the dynamic 

 events with which the experimentalist directly 

 concerns himself. The fruitfulness of this 

 method and ideal of work in morphology, as 

 compared Avith sad sterility of the point of 

 view which vainly attempts to solve in toto 

 dynamic problems by a purely static mode of 

 research as the older morphology did, is ap- 

 parent in the recent history of biology. 



VI 



Jennings has somewhere said that "An ani- 

 mal is something that happens." While this 

 happy phrase might well be taken as the slogan 

 for all modern biology, it expresses with par- 

 ticular aptness the point of view of that 

 major trend in recent biological history in 

 which its author was the one of the most con- 

 siderable pioneei-s and leadei-s, namely the study 

 of animal behavior. The development of this 

 subject into the prominence it has enjoyed in 

 the last quarter of a centurj^ does not repre- 

 sent altogether quite so sharp a break with 

 the philosophy of an earlier time as was the 

 case in the development of experimental mor- 

 phology. The field naturalist had always 

 properly esteemed the importance of things 

 which happened, and there exists, in the older 

 literatu;-e of popular and amateur natural his- 

 tory, a considerable mine of rather accurate 

 observations about the l>ehavio3' and habits of 



