Jan-uary 21, 19 1 5] 



NATURE 



575 



I. 



Fourteen years ago to-night it was my privilege to 

 deliver an address before the American Societ>- of 

 Naturalists, entitled 'Aims and Methods of Stud'v in 

 Natural History,"- in which I indicated certain im- 

 portant changes that were then rapidly gathering 

 headway in zoology. To-night I once more ask atten- 

 tion to this subject as viewed in the fuller light of the 

 remarkable period of progress through which biologv 

 has since been passing. I will not tr\- to range over 

 the whole vast field of zoology or to catalogue its 

 specific advances. I will only' permit mvself a few 

 rather desultory reflections suggested by a retrospect 

 upon the progress of the past twenty-five vears. If 

 my view is not fully rounded, if it is coloured by a 

 long-standing habit of looking at biological pheno- 

 mena through the eyes of an embryologist, I will 

 make no apology- for what I am not able to avoid. 

 Let me remind you also at how many points the 

 boundaries between this and other branches of biologv 

 have become obliterated. The traditional separation 

 between zoology and botany, for instance, has lost all 

 significance for such subjects as genetics or cvtology. 

 Again, the artificial boundan,- often set up between 

 zoology and animal physiology has whoUv disap- 

 peared, owing to the extension of experimental 

 methods to morphology- and of comparative methods 

 to physiology-. I trust therefore that our brethren in 

 botany and physiology — perhaps I should include also 

 those in psychology-— will not take it amiss if I 

 include them with us under the good, old-fashioned 

 name of naturalists. 



The sum and substance of biological inquiry mav 

 be embodied in two questions : What is the living- 

 organism, and how has it come to be .' We often find 

 it convenient to lay the emphasis on one or the other 

 of these questions, but fundamentally they are insepar- 

 able. The existing animal bears the indelible impress 

 of its past; the extinct animal can be comprehended 

 only in the light of the present. For instance, the 

 paleontologist is most directly concerned with prob- 

 lems of the past, but at every step he is confronted 

 by phenomena only to be comprehended through the 

 study of organisms as they now are. Our main causal 

 analysis of evolution must be carried out by experi- 

 mental studies on existing forms. All this seems 

 self-evident, yet the singular fact is that onlv in more 

 recent years have students of evolution taken its truth 

 fully to heart. And here lies the key to the modern 

 movement in zoology of which I propose to speak. 



I do not wish to dwell on matters of ancient historv ; 

 but permit me a word concerning the conditions 

 under which this movement first began to take definite 

 shape as the nineteenth century- drew towards its 

 close. In the first three decades after the " Origin of 

 Species " studies upon existing animals were largelv 

 dominated by efforts to reconstruct their history- in 

 the past. Many of us will recall with what ardour 

 naturalists of the time threw themselves into this 

 profoundly interesting task. Manv of us afterwards 

 turned to work of widely different "type ; but have our 

 later interests, I wonder, been keener or more spon- 

 taneous than those awakened bv the morphological- 

 historical problems, some of them alreadv half for- 

 gotten, which we then so eagerly tried to 'follow? I 

 am disposed to doubt it. The enthusiasm of vouth? 

 No doubt; Kut something more, too. Efforts to solve 

 those problems have in the past often failed; thev 

 no longer occupy a place of dominating importance'; 

 but they will continue so long as biology- endures, 

 because they are the offspring of an ineradicable his- 

 torical instinct, and their achievement stands secure 



- Science, N. S., xiii., No. 314, Januarj- 4, igot. 



NO. 2360, VOL. 94] 



i in the great body of solid fact which they have built 

 I into the framework of our science. Says Poincare : 

 j 'The advance of science is not comparable to the 

 I changes of a city, where old edifices are pitilesslv 

 I torn down to give place to new, but to the continuous 



evolution of zoologic types which develop ceaselesslv 

 j and end by becoming unrecognisable to the common 

 I sight, but where an expert eye finds always traces of 

 j the prior work of the centuries past. One must not 

 ' think then that the old-fashioned theories have been 

 j sterile and vain." 



I After all, science impresses us by something more 

 ; than the cold light of her latest facts and formulas. 



The drama of progress, whether displayed in the 

 I evolution of living things or in man's age-long 

 I struggle to comprehend the world of which he is a 



product, stirs the imagination by a warmer appeal. 

 j Without it we should miss something that we fain 

 I would keep— something, one may suspect, that has 

 , played an important part of the higher levels of 



scientific achievement. 

 1 I seem to have been caught unawares in the act 

 ! of moralising. If so, let it charitably be set down as 

 I an attempt to soften the hard fact 'that thirty vears 

 j after the " Origin of Species " we found ours'elves 

 I growing discontented with the existing methods and 

 I results of phylogenetic inquiry- and with current ex- 

 i planations of evolution and adaptation. Almost as if 

 I by a preconcerted plan, naturalists began to turn aside 

 I from historical problems in order to learn more of 

 I organisms as they now are. Thev began to ask 



themselves whether they had not been over-emphasis- 

 I ing the problems of evolution at the cost of those pre- 



sen ted by life-processes everywhere before our eyes 

 i to-dav. They awoke to the insuflSciencv of their 

 I traditional methods of observation and comparison 

 and they turned more and more to the method by 

 w-hich all the great conquests of phvsico-chemical 

 science had been achieved, that which undertakes the 

 analysis of phenomena by deliberate control of the 

 conditions under which they take place — the method 

 of experiment. Its steadily' increasing importance is 

 the most salient feature of the new zoology-. 



Experimental work in zoology- is as old as zoology 

 itself; nevertheless, the main movement in this direc- 

 tion belongs to the past two decades. I will make no 

 attempt to trace its development; but let me try- to 

 suggest somewhat of its character and conseque'nces 

 by a few outlines of what took place in embr^ology-. 

 The development of the egg has always 'cast 'a 

 peculiar spell on the scientific imagination. As we 

 follow it hour by hour in the living object we witness 

 a spectacular exhibition that seems to bring us very- 

 close to the secrets of animal life. It awakens an 

 irrepressible desire to look below the surface of the 

 phenomena, to penetrate the mystery- of development. 

 The singular fact, nevertheless, is' that during the 

 phylogenetic period of embryological research this 

 great problem, though always'before our eves, seemed 

 almost to be forgotten in our pre-occupation with 

 purely historical questions — such as the origin of verte- 

 brates or of annelids, the homologies of germ-lavers, 

 gill-slits or nephridia, and a hundred others of the 

 same type. Now, these questions are, and always 

 will, remain of great interest; but embrvologv, as 'at 

 last we came to see, is but indirectly co'nnect'ed with 

 historical problems of this type, the embrvologist 

 seeks first of all to attain to' some understanding of 

 development. It was therefore a notable event when, 

 in the later 'eighties, a small group of embrvologists. 

 headed by Wilhelm Roux, turned awav from the his^ 

 torical aspects of embr\-ology and addressed themselves 

 to experiments designed solely to throw light upon 

 the mechanism of development. The full significance 



