60 INTRODUCTION. 



They are attached to a triangular plate, which must he 

 regarded as the labium or under lip, as it closes the ca- 

 vity of the mouth, immediately below the insertion of 

 the trunk. On each side of the latter, not far from the 

 base, there is a minute tuberculiform projection, formed 

 of two or three indistinct joints, which together seem 

 to represent the maxillary palpi. The representative 

 of the labrum or upper lip, is a minute membranous 

 piece, usually approaching to a triangular shape ; and 

 two other smafll projections, more or less ciliated in- 

 ternally, and placed one on each side of the probos- 

 cis at the base, are analogous to the mandibles of 

 gnawing insects. Most of these parts, however, ex- 

 ist in a very rudimentary condition, and afford an- 

 other example, in addition to many already familiar 

 to us, of nature adhering to a particular form of struc- 

 ture, after it has ceased to be subservient to any es- 

 sential function ; for, if some of these parts are de- 

 signed for the same purpose which they serve so ef- 

 fectively when fully developed, it is not easy to see 

 how they could be employed by the insect, or in any 

 way prove serviceable to its economy. 



Both the different kinds of eyes which occur among 

 insects, are to be found in the diurnal Lepidoptera. 

 The ordinary, or compound eyes, are large and he- 

 mispherical, occupying greater part of the head, and 

 no fewer than 17,325 lenses have been counted in 

 one of them. As each of these crystalline lenses 

 possesses all the properties of a perfect eye, some 

 butterflies may therefore be said, if M. Puget's ob- 

 servations are correct, to have no fewer than 34,650, 



