900 



INSECTA. 



the development of which, in the higher forms 

 of insects, is only of secondary importance, com- 

 pared with that of the mandibles, but is now 

 carried to so great an extent that these organs 

 become almost or entirely the sole means of 

 taking food. Not only do these changes take 

 place in the parts of the mouth, but the whole 

 head undergoes a similar alteration in the rela- 

 tive form and size of its parts, occasioned by 

 the excessive development of the organs of vi- 

 sion. Thus in the Lepidoptera, (Jig. 377,) the 



Fig. 377. 



The head and parts of the mouth of Sphinx ligustri. 

 A , antenna j fe, epicranium ', c, cornea ; d, cly- 

 peus posterior ; e, labrum ; f, mandible ; g, max- 

 illa or proboscis ; h, maxillary palpus ; B, base of 

 the maxilla with the mandibles and labrum; C, 

 lateral view of the same. 



lateral and a large portion of the inferior surface 

 of the head is entirely occupied by the corneae 

 (c), which are also extended far forwards upon 

 the anterior. The occipital region is confined 

 to the flat surface that is approximated to the 

 prothorax. The epicranium (6) is distinct, and, 

 as in the preceding Orders, extends as far an- 

 teriorly on each side as the base of the antennae 

 between the cornese, but the suture that sepa- 

 rates it from the clypeus posterior (d) is almost 

 transverse. The clypeus posterior is very large, 

 and occupies the whole of the space between the 

 cornese, on the front of the head. It is convex 

 as in Neuroptera, and is narrowest at its inferior 

 part. The clypeus anterior appears to exist in 

 the form of a minute transverse plate, a little 

 elongated in its middle on the hinder part, and 

 separated by a transverse groove on its anterior 

 from a much smaller plate, the labrum (e), with 

 which it is consolidated. This part, which was 

 first detected in Lepidoptera by the accurate 

 Savigpy,* is also a small convex transverse 

 plate with a little triangular scale at its anterior 

 margin, fitted closely to the front of the max- 

 illae. In Sphinx ligustri, (fig. 377,) the separa- 



* Memoires sur les Animaux sans Vertebres. 



tion of the labrum by suture from the part which 

 we regard as the clypeus anterior, is distinct, 

 but it appears to have been overlooked by Sa- 

 vigny and others. On each side of the labrum 

 are the rudiments of the mandibles (/). They 

 are two minute, iriangular plates, attached in 

 part to the labrum and margin of the clypeus, 

 to which, as Savigny has remarked, they 

 appear to be soldered. They are applied to 

 the base of the maxillae, and in Sphinx appear 

 each to be formed of two parts, and are co- 

 vered along their inner margin with stiff hairs. 

 They are the remains of the large corneous 

 mandibles of the larva. We are indebted for 

 their discovery to the indefatigable researches 

 of Savigny, who first traced their identity. The 

 labium, which forms so conspicuous a part of 

 the mouth in the preceding Orders, like the 

 mandibles, is reduced to insignificance in this. 

 It is a small triangular plate, closely attached 

 to the under surface of the head, at the base of 

 the maxillae, and its division into parts, so dis- 

 tinct in other insects, is now scarcely perceptible. 

 The labial palpi (/c) arise one on each side of 

 the labium. They are usually long, hairy, and 

 three-jointed, and are reflected on the front of 

 the head. Next to the maxillae they are the most 

 conspicuous parts of the mouth, particularly 

 in Pyralidtf and Tortricida, in which they are 

 long and pointed. The lingua has been sup- 

 posed to be entirely absent in Lepidoptera. It 

 was not detected by Savigny. Latreille be- 

 lieved it to exist in the suture at the floor of 

 the mouth, but Mr. Newman has observed a 

 small mammiform protuberance in Sphinx li- 

 gustri which he regards as the analogue of the 

 tongue in this Order. The labrum, mandibles, 

 and labium are entirely concealed by the re- 

 flected labial palpi and a dense clothing of 

 scales, and are only observed when the anterior 

 part of the head is completely denuded of 

 these coverings. Their atrophied condition 

 affords a beautiful illustration of the law that 

 in proportion as the functions of an organ be- 

 come suspended, or are rendered unnecessary 

 by the employment of other parts, the organ 

 itself becomes wasted and utterly useless, and 

 perhaps entirely disappears. Thus in those 

 Lepidoptera whose food is liquid honey pro- 

 duced in the deep chalices of flowers, the 

 short mandibles of the voracious herbivorous 

 larva would be entirely useless to the perfect 

 insect, and its food would be inaccessible 

 to it. Accordingly we find that the man- 

 dibles are now unimportant organs, and 

 the office of conveying food to the mouth is 

 performed solely by the maxillae (</), which 

 are extended in the shape of a long sucking 

 tube. Each maxilla is composed of an im- 

 mense number of short, transverse, muscular 

 rings. It is convex on its outer surface, but 

 concave on its inner, and the tube is formed by 

 the approximation of the two organs. When 

 at rest they are rolled up like a watch-spring, 

 between the large labial palpi, but are capable 

 of being darted forth in an instant. They are 

 the so-called tongue, or proboscis of the but- 

 terfly and moth. Each maxilla has usually 



