xlvi 
probably some more comprehensive law which would account for all those resem- 
blances. 
3rd. It must be shown that the cause of the rarity of the Leptalis was one acting on 
the insect entirely or chiefly while it was in the perfect state; this had not been 
done, and it was improbable that it could be; for the most critical periods in the life 
of Lepidoptera, as regarded their enemies, were the larval and pupal states. 
4th. It must be shown that the enemy (whatever it might be) which attacked the 
Leptalis sought its prey principally by the sense of sight; but this suggested another 
improbability. If the Heliconia, which the Leptalis resembled, was protected by its 
nasty odour, surely the bird or other enemy of the Leptalis must be very fvolish to let 
it escape when it smelt nice, because it looked like the Heliconia. The purpose of 
protection would have been better accomplished by the Leptalis mimicking the Heli- 
conia in that point by which the Heliconia was protected. 
5th. A forcible objection to the mimicry theory (as already pointed out by Prof. 
Westwood) was the rarity of the mimicking species. The theory involved the hypo- 
thesis that there was a time when the Leptalis differed in pattern from the Heliconia; 
was the Heliconia then commoner than now, or as rare? If commoner, it was curious 
that, when not protected, it flourished better than now, when protected. If as rare, 
how could it have survived at all before and during its transmutation? It would, 
perhaps, be suggested that the Leptalis was formerly commoner than now, and that 
some enemy arose, rendering it necessary that the Leptalis should find a new means of 
defence. This, however, was mere supposition, and it was almost impossible to adduce 
facts to prove it; but supposing it to be the case, why did not the enemy exterminate 
the Leptalis when it did not resemble the Heliconia, as (according to the theory) it 
would now, but for this resemblance. The further supposition must he made, that the 
enemy was not at first very dangerous to the Leptalis, and that in proportion as it grew 
dangerous, the Leptalis grew more and more to resemble the Heliconia: it was certainly 
very fortunate for the Leptalis that spontaneous variations, bringing it to resemble the 
Heliconia, should occur in the exact proportion required for its safety. 
6th. Again, taking the time when the Leptalis differed 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. Buta small variation in 
marking would be of no practical service to the Leptalis, especially as it was by its 
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 cerrect at all points, 
Dr. Sharp was of opinion that the evidence as yet adduced was insuflicient to convince 
an unprejudiced observer. The most 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 therefure not likely to produce similarity ! But natural selection was more 
