58 



Two types of insect mouth are readily apparent to every student 

 of the Insecta: — (1) the Mandibidate, in which the four pairs of 

 appendages just enumerated are as a rule quite clear, and (2) the 

 Suctorial, in which usually they are not. Caiiipocha and CoUembnla 

 are to some extent intermediate between these two, the mandibles 

 and maxillae being retracted ; so that, while they can bite soft 

 substances, they are able apparently to suck also. The mouth of 

 Caiiii>odea, one of the most archaic of insects, might be assumed to 

 have been a condition from which the two types branched off ; but 

 conclusions of this kind must not be too readily drawn, and at any 

 rate they do not concern us now. Those interested will find the 

 matter fully discussed in Lord Avebury's " Origin and Metamor- 

 phoses of Insects." 



It is with the appendages of the seventh somite only that we 

 have to do this evening. Before proceeding to consider that organ, 

 however, it will be well to look at the whole of the mouth-parts for 

 a moment. These are found on somites 4, 6, and 7 only, as far as 

 the Paraneuroptera are concerned. On the fourth somite is the 

 pair of strongly toothed horny mandibles ; on the sixth the pair of 

 first maxillae, also armed in part with six teeth ; and on the seventh 

 the united pair of second maxillae, or, as they are usually called, 

 the labium, which covers the mouth ventrally. Dorsally it is closed 

 by a flap (not an appendage of the same nature as the other six) 

 called the labrum. The whole apparatus provides a fairly typical 

 form of mandibulate, or biting, mouth of an archaic insect. 



Possibly these mouth-parts will be more clearly understood if 

 they are shewn dissected out. PI. vii.,fig. A, represents, somewhat 

 diagrammatically, the mouth of an imago of Cordideijaster annidatus, 

 Latr., hairs, etc, being omitted for clearness. If we first examine 

 one of the First Maxillae, which are less modified than the second 

 pair, we shall understand more easily the construction of the latter. 



Essentially a maxilla consists of the cardo, stipes, lacinia, galea, 

 and palpus (omitting one or two less important connecting parts, 

 which do not concern us just now). These can be well seen in the 

 maxillae of a still more archaic insect than a dragonfly (PI. VII., fig. 

 C). In the maxilla of a dragon-fly, however, the lacinia and galea 

 are fused and are usually spoken of as the inner lobe, while the 

 palpus is of a simple nature (PI. VII., fig. B.). Fusion of the same 

 parts has also taken place in the labium, as of course might be 

 expected, fusion in fact being the order of the day in that organ ; 

 and it is easy to see that a useful object is gained thereby — that of 

 keeping the food within the mouth, to be passed on by the first 

 maxillae for thorough crushing by the mandibles. So the two 

 pairs of maxillae fulfil a somewhat similar function to that of the 

 tongue in the vertebrates. 



It seems perfectly clear that originally the second maxillae were 

 less fused than they are in the dragonflies. A glance at the 



