156 TRANSACTIONS OF THE 



Blow-flies (Musca erythrocephala and vomitoria) may be taken as 

 good examj)les of this type. In the Orthorhapha, on the contrary, 

 we have a larva with a more or less well difierentiated head, often 

 bearing antennae ; a good example is that pest of pasttu-e-land — 

 the "grub" of the farmer, the larva of the Crane-fly, for an 

 account of whose ravages I will refer you to Kirby and Spence's 

 " Introduction," a book which ought to be in the hands of every one 

 who desires to know something about our common insects. 



In the perfect or imago state the two sub-orders possess good 

 characters, but these are of too technical a nature to interest any 

 but the specialist. 



The Orthorhapha are subdivided into two groups, the Nematocera 

 and the Brachycera. The first is distinguished from all other 

 Diptera by having antennae with at least six joints — generally 

 many jointed. Other Diptera possess only three-jointed antennae, 

 in some the terminal joint is subsegmented so as to give apparently 

 six or more joints. The Nematocera includes, besides the Cecido- 

 ^myidse or gall-midges, the gnats, crane-flies, and many others. 



The more salient characters upon which the family Cecidomyidse 

 is founded are : wings without alulce, with one transverse and three 

 to five longitudinal nervures ; margin of wing fringed, and the 

 surface hairy. Alula is that false winglet which is found at the 

 base of the wing of the common house-fly and others. 



To Meigen is due the credit of bringing order into the chaos of 

 scattered observations on gall -midges. In the first volume of his 

 " Diptera of Europe," published in 1818, he formulated the charac- 

 ters of the group, which he divided into three genera — Cecidomyia, 

 Lasioptera, and Gampylomyza. Several genera have been added 

 since, and Meigen's Cecidomyia, the principal genxis, is now split up 

 into a number of genera. 



The gall-making larva of a Cecidomyia has a very characteristic 

 and constant shape, sharply tapering to the head and truncately 

 rounded behind. It is divided into fourteen segments ; the head 

 is small, bearing a pair of antennse ; eyes on the third segment ; 

 and has nine pairs of spiracles, one on prothoracic segment or 

 that next to the head, and a pair on each of the first eight abdo- 

 minal segments. 



Not all the larvae of the Cecidomyidm are gall-makers. Some 

 live free under the bark of trees, among rotten wood, or as inqui- 



