DEVELOPMENT OF TEE FORMS OF ANIMAL LIFE. 



481 



DEVELOPMENT OF THE FOEMS OF ANIMAL LIFE. 1 



By Prof. ALLEN THOMSON, M. D., LL. D., F. R. S., F. E. S. E. 



AFTER the long interval of six-and-thirty 

 years the British Association for the Ad- 

 vancement of Science holds its annual meeting, 

 the forty-seventh since its foundation, in this 

 beautiful and interesting locality ; and, strangely 

 enough, on this occasion, as on the former, it 

 passes from Glasgow to Plymouth. We are de- 

 lighted to be assembled here, and are even sur- 

 prised that the Association has been able so long 

 to resist the power of attraction by which it has 

 been gravitating toward this place. While we 

 are prepared to be charmed by the surpassing 

 beauty of its scenery, and know the deep interest 

 of its prehistoric vestiges, its historic memories, 

 and its artistic associations, we have been fre- 

 quently reminded of its scientific vigilance by the 

 records of its active scientific work ; and we are 

 now ready and anxious to witness all we can be- 

 hold of its energy and success in the application 

 of scientific discovery to the practical arts. Should 

 we, as might be expected in a place hitherto so 

 famous in its relations to our naval and military 

 history, find most prominent those relating to the 

 mechanism of war, we shall still hope that the 

 effect of greater perfection in the engines of de- 

 struction may only be the means of rendering 

 peace more permanent and secure. 



It is a source of regret to myself, and may be, 

 I fear, a cause of detriment to this meeting, that 

 the choice of a president should have fallen upon 

 one whose constant occupation with very special 

 branches of science has fitted him so inadequate- 

 ly for the distinguished position to which he has 

 been called. I can only derive comfort from 

 knowing that, wherever it may be necessary, 

 there are many others present most able to sup- 

 ply what may be wanting on my part ; and I 

 must, therefore, at once bespeak their assistance 

 and your indulgence. 



I have selected for the subject of the remarks 

 which I am about to offer for your acceptance a 

 biological topic, namely, the " Development of 

 the Forms of Animal Life," with which my stud- 

 ies have been occupied, and which has important 

 bearings on some of the more interesting biologi- 

 cal questions now agitating the scientific world. 



1 Inaugural address of Frof. Thomson, as President of 

 the British Association for the Advancement of Science, 

 at its Plymouth meeting, delivered August 15, 187T. 



31 



But before proceeding with the discussion of my 

 special subject, it is my desire to call your atten- 

 tion shortly to the remarkable change in the 

 manner of viewing biological questions which has 

 taken place in this country during the last half- 

 century — a change so great, indeed, that it can 

 scarcely be fully appreciated except by those 

 who have lived through the period of its occur- 

 ] rence. 



In the three earlier decades of this century it 

 I was the common belief, in this country at least, 

 ! shared by men of science as well as by the larger 

 body of persons who had given no special atten- 

 tion to the subject, that the various forms of 

 plants and animals recognized by naturalists in 

 their systematic arrangements of genera and spe- 

 cies were permanently fixed and unalterable ; that 

 they were not subject to greater changes than 

 misht occur as occasional variations, and that 

 such was the tendency to the maintenance . of 

 uniformity in their specific characters that, when 

 varieties did arise, there was a natural disposition 

 to the return, in the course of succeeding genera- 

 tions, to the fixed form and nature supposed to 

 belong to the parental stock ; and it was also a 

 necessary part of this view of the permanency of 

 species that each was considered to have been 

 originally produced from an individual having 

 the exact form which its descendants ever after- 

 ward retained. To this scientific dogma was 

 further added the quasi-religious view that in the 

 exercise of infinite wisdom and goodness, the 

 Creator, when he called the successive species of 

 plants and animals into existence, conferred upon 

 each precisely the organization and the properties 

 adapting it best for the kind of life for which it 

 was designed in the general scheme of creation. 

 This was the older doctrine of " Direct Creation," 

 of " Teleological Relation," and of " Final 

 Causes ; " and those only who have known the 

 firm hold which such views had over the public 

 mind in past times can understand the almost 

 unqualified approbation with which the reasoning 

 on these questions in writings like the " Bridge- 

 water Treatises " (not to mention older books on 

 natural theology) was received in their time, as 

 well as the very opposite feelings excited by every 

 work which presented a different view of the plan 

 of creation. 



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