BIOLOGY. 311 



odor, such as to cause birds to avoid eating them, were simulated 

 b_y the females of another group, which had no smell, and might 

 otherwise fall ready victims to birds. By their great resemblance 

 to the obnoxions butterflies, the scentless females were enabled 

 to escape pursuit and deposit their eggs. In different regions 

 there were different species, thus imitating and being imitated. 

 Mr. Wallace conceived that this case was a crucial test of the 

 truth of the Darwinian doctrine. The females least like the Heli- 

 conidte had always been more subject to destruction, and conse- 

 quently by this process of natural selection the present state of 

 very close resemblance had resulted. 



Prof. Huxley cautioned Mr. Wallace against considering this as 

 a decisive case. It was explained quite as completely by the 

 teleological doctrine of the late Dr. Paley. 



Mr. Herbert Spencer thought he could show that the case de- 

 scribed by Mr. Wallace could not be satisfactorily explained by 

 Dr. Paley's teaching. He understood Mr. Wallace that the imita- 

 tion was not complete, and varied in different individuals. This 

 incompleteness was not to be explained were we to assume that 

 the one butterfly was made in imitation of the other by the Crea- 

 tor ; but it was readily accounted for by the law of evolution. 



THE DrPFICULTT OF TRACING ORIGINS. 



Mr. Grove, President of the British Association, in his Inaugu- 

 ral Addi-ess, August 23, 1866, favored the theory of Darwin, 

 while upholding the doctrine of continuity in the universe. He 

 said : — 



" There is nothing, as Prof. Huxley has remarked, like an ex- 

 tinct order of birds or mammals, only a few isolated instances. 

 It may be said the ancient world possessed a larger proiJortion of 

 fish and amphibia, and was more suited to their existence. I see 

 no reason for believing this, at least to anything like the extent 

 contended for ; the fauna and floi'a now in course of being pre- 

 served for future ages would give the same idea to our successors. 

 Crowded as Europe is with cattle, birds, insects, etc., how few 

 are geologically preserved ; while the muddy or sandy margins 

 of the ocean, the estuaries and deltas are yearly accumulating 

 numerous Crustacea and niollusca, with some fishes and reptiles, 

 for the study of future palaeontologists. If this position be right, 

 then, notwithstanding the immense number of preserved fossils, 

 there must have lived an immeasui'ably larger number of unpre- 

 served organic beings, so that the chance of filling up the missing 

 links, except in occasional instances, is very slight. Yet, where 

 circumstances have remained suitable for their preservation, 

 many closely-connected species are preserved ; in other words, 

 while the intermediate types in certain cases are lost, in others 

 they exist. The opponents of continuity lay all stress on the lost, 

 and none on the existing links. But there is another difficulty in 

 the way of tracing a given organism to its parent-form, which, 

 from our conventional mode of tracing genealogies, is never 

 looked upon iu its proper light. Where are we to look for the 



