THE TETRACH^ET^E. 371 



number of setae that accompany the oral apparatus ; 

 thus, the HexaclicetcB have six., the Tetrachcetce four, 

 and the Dichcetce two. 



(331.) The first of these subdivisions, or HEXA- 

 CHIETJE,, comprises insects which, as their very name im- 

 plies, possess a highly organised mouth ; and consequently 

 we observe amongst them those which feed upon the 

 blood of the Mammalia, and for which purpose they 

 were furnished with the apparatus of lancets their 

 mouth contains. They are usually insects of a very ro- 

 bust form; and, by the subdivision of the third joint of 

 their antennae, they appear to indicate their proximity 

 to the Nemocera. Their tarsi are furnished with three 

 vesicles ; and the reticulation of nervures of their 

 wings exhibit high organisation. Amongst these are the 

 Tabaniy and their allies, Hcematopota and Chrysops, 

 all blood-thirsty creatures, and which, in the woods, in 

 summer, constantly alight upon the entomologist's face 

 and hands, and put him to considerable pain. Indeed, 

 it is related that Messrs Kirby and MacLeay were frus- 

 trated in an entomological excursion by the prevalence 

 of these insects, against the severe punctures of which 

 they could find no protection. These are all more or 

 less distinguished for the excessive brilliancy of their 

 eyes whilst alive, which surpass the most vivid gems in 

 lustre, especially the latter genus, which deduces its 

 name from the circumstance. Raphiorhynchus, named 

 from its curved and produced clypeus, and Acanthome- 

 rus, which has spined femora, are large exotic genera 

 peculiar to the Brazils ; and Pangonia longirostris y in 

 which the proboscis is several times longer than the 

 body, is a native of India. 



(332.) The second subdivision, the TETRACH^ET^E, 

 which are deficient in one pair of setae to the mouth, 

 have usually the terminal joint of their antennae simple, 

 or with an apical seta consisting of three divisions, 

 which seem an obsolete indication of its previously de- 

 veloped structure. They have, further, but two vesi- 

 cular soles to their tarsi, and their wings have less com- 

 B B 2 



