356 THE TANYSTOMA. 



Brachycera. But the long, exserted proboscis, which 

 is so striking a character in the Eombylius, is met 

 with in all the other members of the tribe, which 

 has received the name of TANYSTOMA* from this cir- 

 cumstance. This organ, however, is never so long in 

 any of the other British species as in the fly above 

 referred to ; it is generally slender and pointed, rarely 

 terminated by fleshy lips, and almost always encloses 

 four bristles, representing the labrum, tongue, and 

 maxillae, the latter bearing a pair of two-jointed palpi. 



These characters may perhaps appear rather vague 

 for the distinction of a great group of insects, but the 

 truth is, that the Diptera, as a general rule, approach 

 each other in so many different directions, that it is 

 often difficult to define the exact points of distinction 

 even between groups of much smaller extent than 

 the present one ; but that this is a natural group is 

 proved by the nature of the metamorphosis, the pupae 

 being free, whilst in the remainder of the Brachy- 

 ceratous Diptera they are coarctate, or enclosed in 

 the dried larva-skin. The larvae appear generally to 

 live in the earth, and feed upon the roots of plants, 

 but a few are said to be parasitic. 



The majority of the insects of this tribe, however, 

 depart very widely in their habits from the peaceful 

 character of the Bombylii, although a few nearly allied 

 to these, and the males of a good many others, feed 

 exclusively, like them, upon the nectar of flowers. 

 Many, on the contrary, and especially the females, 

 are most predaceous creatures, dashing through the air 

 with great rapidity, seizing upon any unfortunate 

 insect that may come in their way, and sucking out 

 its juices in a very short time. Amongst these is 

 * Gr. tanuo, to extend ; stoma, the mouth. 



