EXTERNAL ANATOMY OF INSECTS. 511 



to palpi : but as they do not proceed from the oral or- 

 gans, but from the bed of the antenna at the base of the 

 nose a , they ought certainly to be regarded rather as ac- 

 cessories to the latter, than as representing the former. 

 In the Aptera order the mites (Acacus L.) appear to be 

 without these organs. In the pupiparous tribe Hippo- 

 bosca they seem about to disappear ; and in the Arach- 

 nida &c, as has been more than once observed b , the 

 mandibular have been thought to represent, not indeed 

 the antennae of insects, but the inner pair of those of the 

 Crustacea. 



In considering the insertion of antennae, by which I 

 mean their articulation with the head, we must advert 

 first to the orifice ( Torulus) that receives them c . This 

 is a perforation of the crust of the head; commonly, 

 though not invariably, circular : in Coleopterous insects 

 often with concave lubricous sides, forming an acetabu- 

 lum, with processes usual in ginglymous articulations, 

 larger than the bulb or root of the antennae; and which is 

 commonly covered, except the central space occupied by 

 the bulb, with a tense membrane. Though not in gene* 

 ral remarkable, in some cases it merits attention. In the 

 genus Rhipicera Latr., the elegant antennae of whose 

 males I have described in a former letter d , particularly 

 the Brazilian species, it is a long process on each side of 

 the nose, and might be mistaken for the first joint : in 

 another Coleopterous genus, Priocera K. e , it has some- 

 what of the shape of a trumpet : in Cupes a tubercle rises 



a Palpi quatuor, subaequales, cylindrici, ad basin clypei. Germ. 



b See above, p. 18, &c. c Plate VI. Fig. 1, 4. i'. 



d See above, p. 321. Linn. Tram. xii. t. xxi.f. 3. 



e Ibid./. 7- 



