SUBDIVISIONS OF THE DIPTEBA. S6$ 



individuals, they certainly surpass all ; no place or time 

 is unfurnished with them, and usually in enormous pro- 

 fusion. Life thus multiplies life; for the multitudes 

 of birds that they support, contributes to vary its exten- 

 sion over the earth; but the chief function that they 

 exercise in the economy of nature, is to contribute to- 

 wards the destruction of those substances which, in a 

 state of corruption, would tend otherwise, by poisoning 

 the air, to produce disease and mortality. Further pe- 

 culiarities in their economy we shall briefly notice as we 

 pass rapidly through the families ; and we shall now, 

 therefore, quit this generalisation, and proceed to the 

 investigation of the contents of the order, and their dis- 

 tribution. 



(S29-) The two primary groups, the NEMOCEBA and 

 BBACHOCERA, into which they have been divided, ac- 

 cording to the number of the joints of their antennae, 

 are of very unequal extent. The first, or NEMOCEBA, 

 are those which possess more than six joints to the 

 organ, and comprises the Cullces and Tipulce. The 

 former are perhaps the most highly organised, in every 

 respect, of all the Diptera; and to the perfection of 

 their suctorial apparatus the majority of us can attest, 

 from our individual experience of what is. called the 

 sting of a gnat. Their larvse are aquatic, and are those 

 singular little red worms, large at one extremity, that 

 we frequently observe in stagnant waters ; they move 

 by a sort of jump ; and, breathing by means of anal 

 tracheae, they frequently resort to the surface, to imbibe 

 a fresh supply of air. These are all small insects, and 

 all the genera are natives of this country, but Cu lea? is 

 the most abundant in species. The Tlpulce } which 

 form the second group, are less highly organised in the 

 structure of their mouths only. The typical genera are 

 well known as " Father long-legs ; " and, in their larva 

 state, many of them are very injurious to the roots of 

 grass. They form a large tribe, subdivided by struc- 

 ture, but named from the places or substances they 



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