.506 EXTERNAL ANATOMY OF INSECTS. 



Though a large number of insects have them, they are 

 by no means universal, since some Orders, as the Stre- 

 psiptera, Dermaptera, and Aptera, are altogether without 

 them. The Coleoptera, also, have been supposed to af- 

 ford no instance of species furnished with them; but in the 

 last number of Germar and Zincken Sommer's Magasin, 

 it is affirmed that they are discoverable in Gravenhorst's 

 genus Omalium, but not in the kindred genera Micro- 

 peplus and Anthophagus a . Upon examining the former 

 genus, I find, that although Omalium planum and affi- 

 nities, O. striatulum, and some others, appear not to have 

 them, yet with the aid of a good magnifier they may be 

 discovered in most species of that genus ; as likewise in 

 Evcesthetus Grav. I find them also very conspicuous in 

 A. Caraboides and other Anthophagi, but some species 

 appear to want them. In these insects they are two in 

 number, situated in the vertex a little behind the eyes but 

 within them, and either at each end of a transverse furrow, 

 or at the posterior termination of two longitudinal ones. 

 Nor are they found in all the genera of the other Orders. 

 In the Orthoptera, the Blattidce, unless a white smooth 

 spot on the inner and upper side of the eyes may be re- 

 garded as representing them, have them not ; but in all 

 the other genera of that Order they are to be found b . 

 In the Hemiptera all the Cicadiadce are gifted with them ; 

 as are likewise Tetyra, Pentatoma, with many other Ci- 



a Magas. der Entomolog.'ix, 410. 



b Latreille speaks of Phasma as having no stemmata; but it should 

 seem that he examined only the apterous ones, all the winged indi- 

 viduals, at least so far as I have examined them, having three very 

 visible ones. It may, I think, be laid down as a rule, that the larvae 

 and pupae of Orthoptera have not these organs. Probably their use 

 is principally in flying? 



