48 IMPORTANCE OP THE MOUTH PARTS. 



It must, however, be confessed that, although these 

 vainous forms, which in their adult condition are so 

 dissimilar, in an early stage resemble one another very 

 closely in the well-developed head, the three thoracic 

 segments each with a pair of legs, the segmented 

 abdomen, the caudal appendages, &c., still in the con- 

 struction of the mouth there are differences of great 

 importance. Yet from another point of view the struc- 

 ture of the mouth seems to me to offer a very strong 

 support to M. Brauer's opinion, and one of which I 

 wonder that he has not availed himself. 



On this point the remarks of Meinert are very im- 

 portant. Admitting the " great importance of the 

 organs of the mouth for the establishment of the prin- 

 cipal as well as subordinate divisions of insects,"^ he 

 says, " the essential point of difference is, in my opinion, 

 to be found in the position of the first two pairs of 

 appendages of the mouth with reference to the skull. 

 One of these two principal types is characterised by 

 the mandibles articulating -with the shull by means of a 

 hinge-joint, while the maxillae are connected with the 

 skull through a less perfect articulation, sometimes 

 merely sliding on its anterior margin, which surrounds 

 the mouth. This arrangement leaves the organs of the 

 mouth entirely free outside the mouth ; they can be 

 moved laterally, and are so far fit for biting ; and whilst 

 the mandibles are altogether incapable of being pro- 

 truded in front of the mouth, the maxillae are only in a 

 very limited degree capable of such a displacement. 

 The appendages of the mouth cannot, therefore, be 

 used as stinging-instruments ; and when they are 

 adapted for sucking, this process is carried on either by 

 means of the lingua, as in bees, or by means of an 

 extension of the oesophagus, as in Glossata. AYhere 

 this arrangement of the mouth is adopted, the skull 

 must possess a certain degree of firmness in order to 

 afford sufficient support for muscles and articulations. 



1 ' Naturliistoi-isk Tidsskiift,' 1865, p. 400 j and 'Ann. and Mag. of 

 Nat. His.,' 1867, p. 362. 



