580 The Zoologist— February, 1866. 



Mr. McLachlan remarked, as bearing upon the theory of Natural Selection, that 

 having recently been engaged in an examination of the British Psocidre, in which 

 family the generic or sectional characters were principally grounded on the neuration, 

 he had found occasional instances of aberration in the arrangement of the veins : 

 these aberrations consisted in one wing of an insect which belonged to a particular 

 genus or section assuming, entirely or partially, the neural characters of another genus 

 or section ; in no case, among several hundred example-;, did he find neural variation 

 which was strictly abnormal. 



Dr. Sharp offered some criticisms on the theory advanced by Messrs. Bites and 

 Wallace, and argued — 



1st. That natural selection was a power of differentiation, and, although it was quite 

 possible that a differentiating power might work so as to produce resemblances, it was 

 at first sight improbable that it should do so; and more evidence was required of the 

 truth of a paradox than a truism. 



2nd. It must be shown that animals possessing the so-called mimetic resemblances 

 occurred far more frequently in company with one another than away from one another. 

 But if this were shown, a single case of such resemblance between animals living in 

 different localities would throw doubt ou the theory, by suggesting that there was, 

 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 seuse 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 foolish 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 poiuted 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 flouri>hed 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, aud 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 iu the exact proportion required for its safety. 



