Ai'KiL 6, 1S99J 



NA rURE 



547 



toplasm forms the basis of life was generally received forty years 

 since ; fifty years ago the doctrine of the conservation of forces 

 was worked out, and already by this time had the idea of the 

 unity of nature dominated the world of science. 



On the fiftieth anniversary, therefore, of our Association, it 

 may not be out of place, during the hour before us, first, briefly 

 to inquire into the present state of evolution and its usefulness 

 to zoologists as a working theory, and then to dwell more at 

 length on the subject of the effect of geological changes on animal 

 life. 



The two leading problems which confront us as zoologists are : 

 What is life ? and, How did living beings originate? We must 

 leave to coming centuries the solution of the first question, if it 

 can ever be solved ; but we can, as regards the second, con- 

 gratulate ourselves that — thanks to Lamarck, Darwin, and others, 

 in our day and generation — a reasonable and generally accepted 

 solution has been reached. 



Time will not allow us to attempt to review the discoveries 

 and opinions which have already been discussed by the founders 

 and leaders of the different schools of evolutionary thought, and 

 which have become the common property of biologists, and are 

 rapidly permeating the world's literature. 



It maybe observed at the outset that, if there is any single 

 feature which differentiates the second from the first half of this 

 century, it is the general acceptance of the truth of epigenetic 

 evolution as opposed to the preformation or incasement theory, 

 which lingered on and survived until a late date in the first half 

 of the present century.' The establishment of the epigenetic 

 view is largely due to exact investigation and modern methods 

 of research, but more especially to the results of modern embry- 

 ology and to the fairly well digested facts we now have relating 

 to the development of one or more types of each class of the 

 animal kingdom. 



To use a current phrase, the evolution theory is now held as 

 come t® stay. It is the one indispensable instrument on which 

 the biologist must rely in doing his work. It is now almost an 

 axiomatic truth that evolution is the leaven which has leavened 

 the whole lump of human intellectual activity. It is not too 

 much to claim that evolutionary views, the study of origins, of 

 the beginning of organic life, the genesis of mental phenomena, 

 of social institutions, of the cultural stages of different peoples, 



1 The theory of incasement {cmboittrtent), propounded by Swammerdani 

 in 1733, was that the form of the larva, pupa and imago of the insects pre- 

 existed in the egg, and even in the ovary ; and that the insects in these 

 stages were distinct animals contained one inside the other, like a nest of 

 boxes, or a series of envelopes, one within tlie other ; or, in his own words : 

 ^' Aniwai in ani/nali, sen fa/>iiio intra erucam reconditus." R^amur 

 (1734) also believed that the caterpillar contained the form of the chrysalis 

 and butterfly, saying : '* Les parties des papillon cach^es sous le fourreau de 

 chenille sont d'autant plus faciles a trouver que la transformation est plus 

 proche. Elles y sont neanmoins de tout temps." He also believed in the 

 simultaneous existence of two distinct beings in the insect. " II serait tres 

 curieux de connaitre toutes les communications intimes qui sent entre la 

 chenille et le papillon ... La chenille hache, broye, digere les aliments 

 qu'elle dislribu^ au papillon ; comme les meres pr^parent ceux qui sont 

 ports aux ftetus. Notre chenille en un mot est destinee a nourrir et a 

 defendre le papillon qu'elle renferme " (Tome i, 8<^ M^moire, p. 363). 



It was not until 1815 that Herold exploded this error, though Klrby and 

 Spence in 1828, in their " Introduction to Entomology," combated Herolds 

 views, and maintained that Swammerdam was right. As late as 1S34, a cen- 

 tury after Swammerdam Lacordaire in his " Introduction k I'Entomologie," 

 declared that "a caterpillar is not a simple animal, but compound," and he 

 actually goes so far as to say that "a caterpillar, at first scarcely as large as 

 a bit of thread, contains its own teguments threefold and even eightfold in 

 number, besides the case of a chrysalis, and a complete butterfly, all lying 

 one inside the other." This view, houever, we find is not original with 

 Lacnrdaire, but was borrowed from Kirby and Spence without acknow- 

 ledgment. These authors, in their '^Introduction to Entomolog>- " (1828), 

 combated Herold's views, and stoutly maintained the old opinions of 

 Swarnmerdam. They based their opinions on the fact, then known, that 

 certain pans of the imago occur in the caterpillar. On ihe other hand, 

 Herold denied that the successive skins of the pupa and imago existed .is 

 germs, holding that they are formed successively from the '■'' rete miuosnm." 

 which we suppose to be the hypodermis of later authors. In a slight degree 

 the Swammerdam-Kirby and Spence doctrine was correct, as the imago 

 does arise from germs, i.e. the imaginal discs of Weismann, while this 

 was not discovered by Herold, though they do at the outset arise from the 

 hypodermis, his rete viitcosum. Thus there was a grain of truth in the 

 Swammerdam-Kirby and Spence doctrine, and also a mixture of truth and 

 error in the opinions of Herold. 



The discovery by Weismann of the imaginal discs or buds of the imago in 

 the maggot of the fly, and his theory of histolysis, or of the more or less 

 complete destruction of the larval organs by a gradual process, and his 

 observation of the process of building up of the body of the imago from the 

 previously latent larval buds, was one of the triumphs of modern biology. 

 It is therefore not a little strange to see him at the present day advocating a 

 return to the preformation views of the last century in the matter of heredity. 

 Of course it goes without saying, as has always been recognised, that there 

 is something in the constitution of one egg which predestines its becoming 

 an insect, and in that of another, which destines it to produce a chick. 



xNO. 1536, VOL. 59] 



and of their art, philosophy, and religion — that this method of 

 natural science has transformed and illuminated the philosophy 

 of the present half-century. ' 



It is naturally a matter of satisfaction and pride to us as 

 zoologists that, though evolution has been in the air from the 

 days of the Greek philosophers down to the time of Lamarck, 

 the modern views as to the origin of variations, of adaptation, 

 of the struggle for existence, of competition, and the preservation 

 of favoured organs or species by selection are the products of 

 single-minded zoologists like Darwin, Wallace, P'ritz Muller, 

 Semper, and Haeckel. It is the work of these men, supple- 

 mented by the labours of Spencer and of Huxley, and the 

 powerful influence of the botanists. Hooker and Gray, all of 

 whom contributed their life-long toil and efforts in laying the 

 foundation-stones of the theory, which has brought about its 

 general acceptance among thinking men. It is these naturalists, 

 some of them happily still living, who have worked out the 

 piinciple of evolution from the generalised to the specialised, 

 from the simple to the complex, from chaos to cosmos. 



The doctrine of evolution has been firmly established on a 

 scientific basis by many workers in all departments of biology, 

 and found not only to withstand criticism from every quarter, 

 but to be an indispensable tool for the investigator. The 

 strongest proof of its genuine value as a working theory is that 

 it has, under the light shed by it, opened up many an avenue 

 of inquiry leading into new fields of research. It is based on 

 the inductive method, the observation and arrangement of a 

 wide series of facts. Moreover it explains a vast complex of 

 facts, and enables us to make predictions, the true test of a 

 scientific theory. Biology is not an exact science, hence the 

 theory is not capable of demonstration like a problem in 

 mathematics, but is based on probabilities, the circumstantial 

 evidence being apparently convincing to every candid, well- 

 trained mind. 



The methods and results of natural science, based as they now 

 are on evolutional grounds, have, likewise, appealed to the 

 historian, the philologist, the sociologist, and the student of 

 comparative religion, whose labours begin with investigations 

 into the origins. 



It goes without saying that, thanks to the initiative of the 

 above-named zoologists, every department of intellectual work 

 and thought has been rejuvenated and rehabilitated by the 

 employment of the modern scientific method. All inquiring 

 minds appreciate the fact that, throughout the whole realm of 

 nature, inorganic as well as organic, physical, mental, moral 

 and spiritual, there was once a beginning, and that from a 

 germ, by a gradual process of differentiation or specialisation, 

 the complex fabric of creation has, by the operation of natural 

 laws and forces, been brought into being. All progress is 

 dependent on this evolutionary principle, which involves varia- 

 tion, adaptation, the disuse or rejection of the unfit, the use or 

 survival of the fittest, together with the mechanical principle of 

 the utmost economy of material. 



Though the human mind has its limitations, and the chief 

 arguments for evolution have been drawn from our observations 

 of the history of our own planet, and of the life existing upon 

 it, the nebular hypothesis teaches us that the .same process has 

 determined the origin of other worlds than ours, and applies in 

 fact to all the other members of our solar system, while with 

 little doubt the principle may be extended to the entire universe. 

 At all events evolutionary modes of thinking have now be- 

 come a second nature with philosophic, synthetic minds, and to 

 such any other view is inconceivable. We teach evolution in 

 our colleges and universities, and the time is rapidly approach- 

 ing, and in some instances has already come, when nature- 



1 It is worthy of mention that ju,st fifty years ago, in his "Future of 

 Science," written in 1848, at the age of twenty-five, Renan, who first among 

 philosophers and students of comparative philology adopted the scientific 

 method. /.(■- the patient investigation of as wide a range of facts as possible, 

 wrote : " I am convinced that there is a science of the origins of mankind, 

 and that it will be constructed one day, not by abstract speculation, but by 

 scienliiic researches. What human life in the actual condition of science 

 would suffice to explore all the sides of this single problem? And still, how 

 can it be resolved without the scientific study of the positive data? And if 

 it be not resolved, how can we say that we know man and mankind? He 

 who would contribute to the solution of this problem, even by a very im- 

 perfect essay, would do more for philosophy than by half a century of 

 metaphysical meditation" (p. 150). Again he says: "The great progress of 

 modern thought has been the substitution of the category of evolution for 

 the category of the 'being,' of the conception of the relative for the 

 conception of tlie absolute, of movement for immobility. Formerly every- 

 thing was considered as 'being '(an accomplished fact); people spoke of 

 law, of religion, of politics, of poetry in an absolute fashion. At present 

 everything is considered as in the process of formation" (p. 169). 



