396 FOOD OF INSECTS. 



the little animals suck up a their repast; thus, forming a 

 pump, which, more effective than ours, digs the well 

 from which it draws the fluid b . 



A third description of insects, those of the order Di- 

 ptera, comprising the whole tribe of flies, have a sucker 

 formed on the same general plan as that last described, 

 but of a much more complicated and varied structure. 

 It is in like manner composed of a grooved case and 

 several included lancets ; but the case, although horny, 

 rigid and beak-like in some, is in others fleshy, flexible, 

 and more resembling the proboscis of an elephant, and 

 terminates in two turgid liplets : and the accompanying 

 lancets are themselves included in an upper hollow case, 

 in connexion with which they probably compose an air- 

 tight tube for suction. The number and form of these 

 instruments is extremely various. In some genera [Mus- 

 ed) there is but one, which resembles a sharp lancet. 

 Others (Empis, Asilus,) have three, the two lateral ones 

 needle-shaped, that in the middle like a scymetar ; to- 

 gether forming so keen an apparatus, that De Geer has 

 seen an Asilus pierce with it the elytra of a Coccinella ; 

 and I have myself caught them with not only an Elater 

 and Curcitlio, but even a Hister, in their mouths. In 

 many Tabani we find four; two precisely resembling 



a The mode, however, in which this is effected in all insects fur- 

 nished with a proboscis, can scarcely be by suction, strictly so called, 

 or the abstraction of air, since the air-vessels of insects do not com- 

 municate with their mouths : it is more probably performed in part 

 by capillary attraction ; and, as Lamarck has suggested, (St/st. des 

 Aram, sans Vertebrcs, p. 193.) in part by a succession of undulations 

 and contractions of the sides of the organ. 



b Plate VI. Fig. l(i— 19. 



