AN ACCOUNT OF BRITISH FIIES. 



Order Diptera. 



Mouth suctorial, and used for piercing, the labium being greatly 

 developed and forming a gutter for the reception of the lancets 

 (maxillai and mandibles). 



This proboscis, which is chiefly made up of the labium, ends in a 

 fleshy swollen tongue, and is without palps. It is closed above by 

 the labrum. 



The maxillffi are provided with palps ,; the mouth, however, may 

 be obsolete or closed. 



The head is usually large and spherical, and is attached to the 

 thorax by a short neck. Two large facetted eyes are present, and 

 there may be ocelli as well. In the <^ the eyes may join in the 

 middle line, this being a valuable way to distinguish sex. 



The antennae are of two forms, (a) long and filiform, and composed 

 of many joints ; or (/3) short, with the third joint inflated, and bearing 

 two or three tapering joints or a bristle. 



The thorax is usually large and compact ; the prothorax very much 

 reduced, and attached as a collar to the mesothorax, which is very 

 large and is developed at the expense of the other two regions of the 

 thorax. 



One pair of true wings only developed, these being the anterior 

 ones, and are usually transparent and never folded, with an inferior 

 basal lobe. Veins crowded in front, distant behind. Cross veins 

 few. 



The hind wings reduced to small club-shaped lamina, known as 

 halteres. Both may be absent. The abdomen generally small, but 

 may be elongated, as in the TipulidcC, and composed of five to nine 

 segments. 



Legs six in number, and slender, having five jointed tarsuses, 

 ending in ungues or " pads " for attachment. The nervous system 

 presents various modifications — in some the ganglia of the thorax 

 and abdomen become fused, or there may be three thoracic ganglia 

 and five or six abdominal ganglia. The male genital organs consist 

 of two testes with vasa deferentia and copulatory appendages. 



The female have three receptacula seminis in connection with the 

 vagina, and in some cases have a retractile ovipositor. 



Having given a short general description of the Diptera we can 

 now pass on to the review of the fossil species. In dealing with the 

 ancestral forms of our flies, we include those found in all parts of 

 the world, as very few have been discovered in England, compared 



