The Zoologist — February, 1866. 581 



6th. Again, taking the time when the Leptalis diffeved in pattern from the Heli- 

 conia, it was said that specimens exhibiting small variations approximating to the 

 Heliconia were selected for the preservation of the species. Bui a small variation in 

 marking would be of no practical service to the Leptalis, especially as it was by Us 

 nasty odour that the Heliconia was protected; to which it might be added that on the 

 theory of Natural Selection no reason or fact was brought forward to induce the belief 

 that variations of the required sort should occur at all. 



In conclusion, whilst admitting the impossibility that such a theory as that of 

 mimetic resemblances could ever be shown by facts to be correct at all points, 

 Dr. Sharp was of opinion that the evidence as yet adduced was insufficient to convince 

 an unprejudiced observer. The roost that could at present be said of the theory was, 

 that it was very ingenious, and might or might not be true. 



Mr. Wallace, in replying to Dr. Sharp, remarked that it was very easy to make 

 objections to any theory, and many of those advanced were of such a general nature 

 that it would require the whole subject to be again fully gone into to answer them in 

 detail. The first objection was one of those vague and general.statements which was 

 really no objection at all ; it was said that natural selection being a power of differen- 

 tiation, was therefore not likely to produce similarity ! But natural selection was more 

 than a power of differentiation; it was the preservation and accumulation of useful 

 variations; and the moment it became useful to one creature to resemble another, all 

 variations which tended to make it so would be preserved, and would accumulate till 

 an outward similarity was produced. In answer to the second objection, Mr. Wallace 

 admitted that it must be shown that pairs of mimetic insects occurred together more Ire- 

 quently than apart, and maintained that this had been shown : he denied that a single 

 case of mimicry by insects of different countries would discredit the general 

 explanation ; since in one case the resemblance might easily be accidental, or recent 

 chan-es of distribution might have parted creatures that once lived together. But, 

 however this might be, even one case of mimicry among insects from distinct countries 

 (as complete and striking as many of those adduced by Mr. Bates and the speaker) 

 had not yet been produced by the oppouents of the theory. Dr. Sharp, as a third 

 objection, required proof that the scarcity of Leptalis was owing to persecution in the 

 perfect state, not in the larval or pupal conditions ; probably Dr. Sharp could not give 

 such proof in the case of a scarce British insect which he had studied for years, and it 

 was quite immaterial to the question. The Leplalides alone of all Pierids were 

 universally scarce in individuals, and almost all the Leptalides, and they alone, mimic 

 Helitoniida;. As to requiring proof that birds seek their prey by the sense of sight, it 

 was so generally admitted that insectivorous birds captured their prey by sight, that if 

 Dr. Sharp denied it he should rather prove that they do not. In the next place, it was 

 asked, " Was the Leptalis, before it resembled the Heliconia, abundant or rare ? If 

 abundant, then it was belter off without protection than with it. If rare, how did it 

 survive at all before and during transformation?" The reply was, that before the 

 Leptalides began to mimic the Heliconise they were more abundant than now, and 

 like nations aud individuals, they were better off when they did not require protection, 

 than now when they cannot exist without it. The Leptalides were not now the same 

 insects they were then, and their conditions of existence had also materially changed 

 since that remote epoch. Lastly, it was said that as the Heliconia? were protected by 

 their disagreeable odour, a superficial resemblance to the Heliconia? could not be at 



