THE INTEGUMENTAL SKELETON OF THE IMAGO. 



portion of the under-lip, which is composed of these united 

 with the mentum, or chin, and the tongue (ligitla). The third 

 pair of jaws have the chin behind and below them, and the 

 tongue above and before them (between their terminal lobes on 

 their oral surface) and always united with them through its 

 coalescence with the remarkable labial palpi.' 



The nature of this tongue has led to much discussion. 

 Savigny called it the ' hypopharynx,' and erroneously supposed 

 it to be a mere process of the floor of the pharyngeal cavity. 

 It is really always a tongue-like process of the floor of the 

 mouth, which either overhangs or surrounds the extremity of 

 the duct of the great salivary (lingual) glands, and it arises 

 from the base of the labiurn. It may be fleshy as in the Cock- 

 roach, reduced to the form of a hollow seta as in the Diptera, 

 or many-jointed as in Bees. It is frequently fringed by tactile 

 or gustatory bristles and papillae. When Savigny named it the 

 ' hypopharynx ' in the Flies, he entirely overlooked its real 

 nature. 



In the more generalised Insecta, although the appendicular 

 portion of the labium, the modified second pair of maxillae, con- 

 sists of parts which can be more or less readily recognised as 

 corresponding with the parts of the first pair, they are never so 

 large or complex, and there is a distinct tendency for them to 

 become obsolete in all the more highly modified forms. In the 

 Lepidoptera nothing remains but their palpi, and in the Bees 

 they are reduced to the form of a pair of scales, the paraglossae, 

 and a pair of long-jointed palps. 



The palpi are apparently the last parts which remain in the 

 most highly modified types, and even these are generally 

 regarded as obsolete in the Diptera and Hemiptera in which, 

 according to received views, the second pair of maxillae (labium) 

 play such an important part in the structure of the suctorial 

 mouth. 



The Maxillae (or first pair of maxillae). Brulle very carefully 

 figured and compared the maxillae of numerous insects. I give 

 a copy of some of his figures of the maxillas and labium of a few 

 well-marked types (Fig. 26). A typical maxilla consists of 



