16 EXTERNA!. ANATOMY OF INSECTS. 



mode of their development affords cliaracters by which 

 classes are distinguished; the degree of their development, 

 and the variation of their form, those for subordinate divisions. 

 The diminution of a part until it escapes our notice is no 

 proof of its non-existence ; otherwise, the discovery of a part 

 by a highly-magnifying power might be termed its creation. 

 In the foregoing table, it will be seen that there are some parts 

 originating in, and totally dependent on, the others. These 

 are the feelers and galea; which may be termed secondary 

 parts. Now secondary parts cannot exist without the pri- 

 mary parts which bear them. The presence of labial-feelers 

 ensures a labium ; the presence of maxillary-feelers ensures a 

 maxilla. I feel considerable hesitation in considering the 

 tongue, or hi/pop/iarj/nx of Savigny, a primary part. It is, 

 however, of little moment what nominal value we may set on 

 it. Its importance is precisely that of the tongue in the human 

 mouth. It originates at the pharynx in common with the two 

 lips, and is a portion of the same section. 



The situation of the mouth is commonly in the lower part 

 of the head, a little forward, calculated for feeding readily 

 while the liead is naturally inclined ; it is bounded above 

 by that part of the skull called the clypeus, and below by 

 that part termed the mentum, from both of which it is per- 

 fectly distinct. I will now endeavour to trace the variations of 

 its parts. 



The first part of the mouth is the Labrum, or upper lip. 

 Fabricius, in describing this part, is very inaccurate. He has 

 confounded it with the clypeus. He describes its variations in 

 different genera. He alludes in one genus to the clypeus, in 

 another to the labrum ; in a third he unites the two. You will 

 remark, it is never sutured to the skull ; it is always free, move- 

 able, and distinct. It unites with the lower-lip, and forms with 

 it a distinct section. It bears on its under side the Epipharynx. 

 It is usually an osseous piece, freely articulated to the clypeus, 

 and originating below and within it. It is of variable shape ; 

 never palpigerous ; and it serves as a cover to the other parts 

 of the mouth. In LepidojHera, the upper-lip is an unimportant 

 part, and appears to have escaped the notice of naturalists, 

 until detected by the accurate Savigny.* It is a thin flat scale- 



• On voit d'abord que la livre sup6rieure doit etre trds petite et trte peu 

 apparente ; elle est mince, membrancusc, quelquefois dcmicirculaire, mais le plus 



