Entomological Society. 9087 
one species must imitate another, he (Prof. Westwood) thought it far more probable 
that the variation would consist in getting stronger muscles to their bodies, as in the 
species of Charaxes he had that evening exhibited, rather than in a minute change in 
the curve of the wing. 
Captain Cox thought that the swiftest fliers had the straightest wings, as, e.g., the 
Sphinges, where the costa was scarcely arched at all. 
Mr. Newman also was unable to connect an arcuate wing with rapidity of flight, 
and instanced the straight coste of the swift-flying Diptera. 
Mr. F. Smith referred to some of the swifiest Hymenoptera, which had pointed 
wings, but with perfectly straight coste. 
Mr. Baly said that the arched form of wing might be advantageous in giving a 
greater power of twisting and turning about, rather than in giving greater rapidity of 
flight; and this, he thought, was what Mr. Wallace had suggested. 
The President observed that the theory seemed to be based upon the supposition of 
a gigantic persecution to which the butterflies had been subject; but was there any 
evidence of the existence of such persecution? bad Mr. Wallace ever seen the insects 
actually pursued by birds or other enemies? It seemed to him that persecution, to 
the extent to which it now occurred, was altogether inadequate to account for the 
magnitude of the result attributed to it. 
Mr. Bates said that he had frequently observed in South America that the paths 
were strewn with the wings of butterflies; and in this country it was not an uncommon 
sight to see the Pontie pursued by birds, and sometimes escaping by means of their 
tortuous or “ dodging” flight. i 
Captain Cox had recently seen forty or fifty specimens of Brephos notha destroyed 
by tom-tits in a single morning. 
Mr, F. Smith remarked that, on the persecution principle, great change must be 
impending in the shape of wing of the butterflies of the London district. 
Prof. Westwood asked whether Mr. Wallace had observed the twisting or 
“dodging” flight to be conspicuous in the butterflies which have largely-developed 
wing-tails? or whether the tails contributed to or affected the flight in any, and, if 
any, in what manner? 
Mr. Wallace replied that he had not observed that the wing-tails had any influence 
upon the flight of the insect; he did not think they affected the rapidity, or that they 
acted as a rudder, and he was at a loss to assign any use to those appendages. With 
respect to the other points which had been touched upon, there was in some cases an 
increase of muscular power as well as an increase of curvature of the wings, but the 
wing of a butterfly was far more liable to variation than the body of the insect; that 
organ was therefore more accessible to the operation of the principle of selection, and 
a modification of its form was cousequently more readily produced. Most of the 
instances of swift-fliers with straight wings which had been adduced (as e.g. the 
Sphinges) were insects with the strongest bodies and the greatest muscular power; 
moreover, he did not maintain that any insect with arched wings would have a more 
rapid flight than any other with straight wings; all that he had argued was, that, as 
between two closely allied species, the one which had the wings most arched would 
have the flight most rapid ; for instance, he should expect a Sphinx with arched wings 
to fly more rapidly than a Sphinx with straight wings. But in truth, though he had 
referred to the supposed concomitancy of falcate wings and a rapid flight, his own 
notion was (as had been correctly stated by Mr. Baly) that the arched form was 
