38 INTERNAL ANATOMY OF INSECTS. 



cally, may be regarded in numerous cases as a mouth 

 closed by lips. In caterpillars and many other insects, 

 the substance of the crust where it surrounds the spiracle, 

 is elevated so as to form a ring, round it. The lips, pro- 

 perly speaking, are formed of a single cartilaginous piece 

 or platform, with a central longitudinal cleft or opening, 

 when closed often extending the whole length of the 

 piece a ; but in some appearing always open and circu- 

 lar : of the former description are those covered by the 

 elytra in the common cockchafer ; and of the latter, those 

 that are not so covered : in some, as in the antepectoral 

 pair of the mole-cricket, there appear to be no lips, the 

 orifice being merely closed with hairs b . Though the 

 aperture is usually in the middle of the platform, in the 

 female of Dytiscus marginalis, it is nearer the posterior 

 side, the anterior or upper lip being the longest. In the 

 majority, the mouth or cleft is nearly as long as the spi- 

 racle; yet in the puss-moth (Centra Vinuld] it is shorter c . 

 Some spiracles, however, are unilabiate, or have only 

 one lip. This is the case with Gonyleptes and perhaps 

 others d . The lips are usually horizontal, but sometimes 

 they dip so as to make the spiracle appear open. 



With regard to the substance of these organs, it is more 

 or less cartilaginous, and probably elastic ; the surface 

 frequently appears to be corrugate or plaited; this is very 

 distinctly seen in the stag-beetle and the cockchafer : in 

 the last insect, under a powerful magnifier, we are told 

 that the lips appear to consist of parallel cartilaginous 

 processes, separated by a cellular web e . In some species 



a PLATE XXIII. FIG. 2. b Sprengel, Commentar.. 7. 



c Ibid. t. iii./. 30. PLATE XXIX. FIG. 23. 



* Ibid. 8. 



