ii FOOD OF INSECTS 59 



far behind. It differs widely in the various orders, 

 it differs in the families, it does not always remain 

 constant throughout the lifetime of the individual, 

 often there is an absolute dissimilarity between the 

 mouth of the larva and that of the perfect insect. 

 The mouth parts may, however, be broadly divided 

 into two kinds : those made up of mandibles or jaws 

 for comminuting food, and those forming a haustellum, 

 or instrument for the suction of liquids without distinct 

 manducatory organs. This difference of structure 

 affords a natural opportunity for separating the 

 Insecta* into two great tribes or sections the 

 Mandibulata and Haustellata, or mandibulate and 

 suctorial groups. 



It is possible to reduce the vast differences of the 

 jaws and eating apparatus to a still more elementary 

 basis of structure. From this point of view the 

 mouth of an eating or mandibulate insect is 

 very instructive. Take that of a beetle or grass- 

 hopper. It consists chiefly of six parts, of which 

 four arc lateral and disposed in pairs, the other 

 two are opposed in the opposite direction, thus :': 

 There is the labrum, or upper lip ; on either side are 

 the first pair of jaws, or mandibles ; then come a 

 second pair of jaws, the maxillae ; and finally, below 

 the mouth is a lower lip, or labium, articulate with 

 the chin-piece. The curved articulated appendages 

 with which the maxillae and labium are externally 

 provided are known respectively as the maxillary 

 and labial palpi. In the jaws of many larvae, 

 of a caterpillar for example, the form of the 

 mouth-parts is almost precisely identical. The upper 



