chap, iv.] MOUTH ORGANS OF INSECTS. 129 



articulated to the sides of the head, they can be 

 moved by muscles from side to side, while, thanks to 

 the absence of the articulation, they can be pushed out 

 or drawn in ; they are, in fine, capable of acting either 

 as cutting or as stabbing organs, and it is in them, 

 therefore, that we must look for that indifferent ar- 

 rangement from which both the mandifoiilate and 

 haustellate type of mouth organs have had their 

 origin. 



The former is well seen in the ancient group of 

 the Orthoptera, and is easily demonstrated by the 

 familiar example of the cockroach. In this form it is 

 quite easy to recognise the three pairs of gnathites 

 which, in insects, form those organs of the mouth 

 which are derived from modified appendages, the one 

 pair of mandibles, and the two pairs of maxillse. 



In front of the mouth there is an upper lip or 

 labriim, which has the form of a movable flap ; 

 behind it lie the mandibles (Fig. 60 ; md), modified 

 appendages, of which no part other than the basal 

 remains, all signs of a palp having completely dis- 

 appeared; these work from side to side, and have 

 their inner edge strongly toothed, so that they act as 

 efficient biting organs. 



Behind these we find the first pair of maxillae, 

 organs of some size and complexity ; the basal piece 

 or cardo (ca) is articulated to the head, and has, 

 at right angles to its long axis, the second joint or 

 stipes (st) ; this can move in a lateral direction, and 

 is continued forwards into a soft galea (go), and an 

 internally placed lacinia (la), the inner edge of 

 which is toothed, though not so strongly as the 

 mandibles. Attached to the outer side of the stipes 

 is the so-called palp. 



The second pair of maxillse are still further modi- 

 fied, presenting as they do confluence of the basal 

 portions, which in most air-breathing Arthropods is 

 J 16 



