Chap, iv.] MOUTH ORGANS OF INSECTS, 131 



The mouth organs of the Neuroptera are 



strictly comparable to those of the Orthoptera ; but 

 we see an advance in the fusion of the lateral halves 

 of the labium, while the biting mandibles are grooved 

 on their inner face, and the first pair of maxillae are 

 slender, and are so arranged as to close the groove, 

 and to give rise to a pair of organs which serve as 

 tubes for the passage of the juices of the prey which 

 they have first bitten. 



In the allied Trichoptera (caddis flies) the 

 mandibles are reduced to membranous rudiments, and 

 the maxillae and labium are closely united, and at 

 their base come to be tubular in form. 



In the Coleoptera (beetles) the biting powers of 

 the mandibles seem to reach the maximum of their 

 development, and the labium has the mentum and 

 submentum united into single piece. 



In the Hymenoptera (bees and wasps) the 

 mandibles still retain their biting function, but the 

 maxillae are modified to serve as licking and sucking 

 organs ; the ligula and the first pair of maxillae are 

 greatly elongated, and the latter apply themselves to 

 the sides of the former, giving rise with it to a 

 tubular apparatus, which comes into play after the 

 elongated ligula (or its accessory piece) has licked up 

 the honey on which their possessor depends. 



The conversion of the mouth parts into a sucking 

 organ is most completely seen in the butterfly 

 (Lepidoptera) ; the mandibles are reduced to 

 mere rudiments, and the first pair of maxillae 

 are greatly elongated ; the inner face of each of 

 these last is deeply grooved, and the edge of the 

 grooves minutely denticulated in such a manner that, 

 when one maxilla is applied to its fellow of the 

 opposite side, it combines with it to form a closed 

 tube ; the labium is reduced, and its palps are often 

 very small or evanescent. The sucking tube may 



