39 



. some assistance in the management of the wings during flight. 

 In the Lepidoptera we have seen that the wings are largely without 

 the tactile (or other sensory) bristles that are so abundant on the 

 wings of many other insects, and which are no doubt chiefly useful 

 in keeping the directing nervous centres fully informed of the 

 movements of the wings, and of the varying air pressures they meet 

 with, and consequently precisely what work they are doing, and 

 what variations in their movements are necessary to produce any 

 desired result. 



It is certainly easy to see that if the centres of these circles are 

 moveable diaphragms, they would admirably serve this purpose, 

 acting much in the same way as the rubber bags and tubes that 

 have been utilised in many instruments of research for recording 

 variations of pressure and movement. 



Such a function for them has not, perhaps, much doubt thrown 

 upon it by the circumstance that we are inclined to regard the 

 wing, but perhaps without any good reason, as in a manner dead — 

 dead in the sense that superficial cuticular structures are dead : an 

 idea that is perhaps largely originated by the fact that butterflies 

 seem incommoded to a very slight degree by loss of scales from the 

 wings and by their being more or less tattered and torn, and aided 

 by what we know of the active circulation and other vital processes 

 that go on in a wing up to the time of its complete expansion, when 

 they apparently cease. 



I do not think, however, because no further growth or develop- 

 ment takes place, that we can jump to the conclusion that the 

 wing may not be provided in one way or other with the necessary 

 sensory apparatus for guiding its control during flight.* 



Another wing structure is one that Professor Packard called our 

 attention to twenty years ago, but with which you may not be 

 familiar. This is the "Cocoon-cutter," which is especially developed 

 in Attacus luna, and according to Professor Packard's own observa- 

 tions is used by that insect to cut through the silken threads of the 

 cocoon when the moth emerges. It is a structure that exists 

 apparently in all the Saturnian group, but is best developed in 

 some of the North American species. It is one of the separate 

 chitinous pieces that lie between the wing and the thorax, 

 rather behind the middle line of the fore-wing. It is a piece that 

 exists probably in most Lepidoptera and moves nearly with the wing, 

 but with some little restriction. But in these Saturnians instead of, 

 so to speak, coming to the surface only, it projects above it as a 

 sharp point, and in Attacus luna as a knife or saw, and when the 

 wings are yet unexpanded and folded down, easily projects laterally 

 in a very effective manner. 



* It has been pointed out that the wings are certainly sensitive, as evidenced 

 by a moth moving away with symptoms of discomfort when sunlight is con- 

 centrated by means of a lens on a portion of wing where it would not affect 

 the insect's body. 



