2o6 INJURIOUS AND USEFUL INSECTS 



semblance no doubt protects them from insectivorous 

 birds. 



The Sub-orders of Diptera 



The classification of the Diptera as set forth in recent text- 

 books presents the greatest possible difficulties to beginners. 

 It is often uncertain, owing to incomplete knowledge ; it in- 

 volves characters taken from the pupa, and therefore is not 

 capable of verification by those who have only the fly before 

 them ; lastly, it rests in great part upon minute and obscure 

 details. We shall substitute for the purposes of this book a 

 simpler grouping of the families. 



Two sub-orders of Diptera can be easily distinguished. 

 These are the Neniocera and the Athericera,* of which the 

 Nemocera are relatively primitive, while the Athericera are 

 specialised in a very high degree. The student who is familiar 

 with the structure and life-history of the harlequin-fly and the 

 blow-fly, can take these as types of the two divisions. In 

 Nemocera the antenna never contains fewer than six joints, 

 which are similar to one another, and look like a row of beads ; 

 the second joint, however, may be enlarged, especially in the 

 male (see the harlequin-fly. Lesson 23). The larval skin is 

 cast at pupation in the usual way, and the pupa is in its main 

 features hke a Coleopterous or Hymenopterous pupa, consist- 

 ing merely of the body of the fly enclosed in a transparent 

 pupa-skin. In the Athericera the antenna always takes the 

 plate-and-bristle form. There are three basal joints, the third 

 being much longer than the rest, and the bristle springs nearly 

 from its base. The larval skin is not cast at pupation, but 

 shrinks into a barrel-shape, hardens, and protects first the 

 resting larva, afterwards the pupa. The fly escapes from the 

 larval skin by pushing off with its head the anterior segments, 

 which separate along a transverse Hne.t 



* Nemocera — i.e. with thread-like antenriEe ; Athericera — i.e. with 

 bristle-bearing antennee. 



t The classification here adopted is that of Baron Osten Sacken, who 

 explains his views in these words (slightly abridged) : 



" Macquart had two sub-Orders, Nemocera and Brachycera ; Brauer 

 had also two, Orlhorrhapha and Cyclorrhapha, but the dividing line 

 between them was at a different place from that of Macquart's. I adopt 

 three sub-Orders, and call them Orlhorrhapha Nemocera, Orthorrhapha 

 Brachycera, and Cyclorrhapha Athericera. In other words, I adopt 



