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The answer was, that different insects preserve their existence by different means; one 
may escape by means of its power of flight, the habits of a second may enable it to 
avoid its foe, a third may owe safety to its colour, whilst a fourth may be positively 
distasteful to animals which prey upon insects. Thus the Danaide, though slow of 
flight, were very abundant and were the subjects of mimicry or imitation by other 
species; in all probability they owed their immunity from destruction to the strong 
and unpleasant odour which they indubitably possessed. It was manifest that where 
another means of escape already existed, the principle of selection would not be 
brought into play; the peculiar form of Wing would not be wanted, and therefore 
would not be acquired. The obscure Satyride were doubtless protected by their 
colour; the majority of the Nymphalide had already sufficient power of flight, aud 
those of that group which had acquired the arched form of wing were precisely the 
species which possessed only about the same power of flight as a Papilio. The single 
Celebesean Papilio which had not assumed the arcuate form of wing was one belonging 
to the Polydorus group, a group which was itself imitated by other Papiliones, and 
which therefore was doubtless provided with some special defence, though the nature 
of it was unknown to us. 
Prof. Westwood, after remarking upon the pleasure he always derived from 
Mr. Wallace’s speculations, whether he agreed with them or not, said that he was 
unable to follow Mr. Wallace in tracing the phenomenon to the causes assigned by 
him; arched wings were not necessarily, or even generally, accompanied by the 
greatest rapidity of flight; and if the original form of the butterfly must be varied, if 
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.y., 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 swiftest 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? had 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. 
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. 
