310 LEPIDOPTERA CHAP. 



the maxillary palpi are largely developed, flexible and slender. 

 According to Walter various forms of palpus intermediate between 

 that of Micropteryx and the condition of rudimentary tubercle 

 may be found amongst the Microlepidoptera, 1 



LABIUM. The labial palpi are usually largely developed, 

 though but little flexible ; they form conspicuous processes 

 densely covered with scales or hairs, and curve forwards or up- 

 wards, rarely downwards, from the under side of the head, some- 

 what in the fashion of tusks. The other parts of the labium 

 are frequently represented merely by a membranous structure, 

 united with the maxillae and obstructing the cavity of the 

 pharynx. Where the proboscis is absent it is difficult to find 

 any orifice leading to the alimentary canal, such opening as 

 may exist being concealed by the overhanging clypeus and 

 labium. In some forms, Saturnia, e.g., there appears to be no 

 buccal orifice whatever. In Hepialus the labium is in a very 

 unusual condition ; it projects externally in the position usually 

 occupied by the labial palpi, these organs being themselves 

 extremely short. It is very difficult to form an opinion as to 

 the structure of the labium and other mouth -parts when the 

 maxillae are not developed, as in these cases the parts are of 

 a delicate membranous nature, and shrivel after death. This 

 is the explanation of the fact that in descriptive works we find 

 vague terms in use such as " mouth aborted " or " tongue absent." 



The mouth of the Lepidopterous imago is a paradoxical 

 structure ; it differs very greatly from that of the larva, the 

 changes during metamorphosis being extreme. We should thus 

 be led to infer that it is of great importance to the creatures ; 

 but, on the other hand, the various structures that make up the 

 mouth, as we have remarked, are frequently absent or reduced to 

 insignificant proportions ; and even in forms where the apparatus 

 is highly developed the individuals seem to be able to accomplish 

 oviposition without taking food, or after taking only very minute 

 quantities. It is therefore difficult to understand why so great 

 a change should occur during the metamorphosis of the Insects 

 of this Order. It has been ascertained that in some forms where 

 the mouth is atrophied the stomach is in a correlative condition ; 

 but we are not aware that any investigations have been made 

 as to whether this correspondence is general or exceptional. 



1 Jena. Zdtschr. Natunv. xviii. 1885, p. 168. 



