DIPTERA (TWO-WINGED ELIES). 
63 
W.C. ; or John Browning, 63, Strand, London, W.C. : price about 
15s.). The magnifying-power should not be too high — from 10 to 
15 diameters is about the best. 
Cork-carpet or pith. — Two or three sheets about 6 inches square, 
on which to perform the operations of pinning, etc. (Cork-carpet 
can be obtained at Harrod's Stores, Brompton Boacl, London, S.W.) 
Two or three cork-lined entomological store-boxes. — These can be 
obtained from Messrs. Watkins & Doncaster, or any other dealer in 
natural-history apparatus. For a collecting trip or expedition of some 
duration the boxes should not be smaller than about 18 inches by 12, 
and they must be sufficiently deep to prevent the heads of the pins 
from coming into contact when both sides of the box are filled. 
Should the collector run out of store-boxes, cigar-boxes, in the 
bottom of which is fixed a layer of cork-carpet or pith, make 
efficient substitutes ; but if pith is used, it should not be less than 
| inch thick. 
HOW TO DISTINGUISH DiPTERA FROM OTHER INSECTS. 
Diptera may be distinguished from all other insects by the fact 
that they possess only one pair of wings. Thus, besides ordinary 
flies, such as Blue-bottles and House-flies (Muscidce), the order also 
includes Midges (Chironomidce), Gnats or Mosquitoes (Culicidce), 
Daddy-long-legs (Tipulidce), Horse-flies {Tabanidce), etc. 
HOW TO DISTINGUISH THE SEXES. 
In the majority of Diptera the sexes may easily be distinguished 
by the fact that the eyes meet together (or nearly so) on the fore- 
head in the male, but are more or less widely separated in the 
female. With the exception, however, of a few small families, 
this does not apply to the Othorrhapha Nematocera [Gall-midges 
(Cecidomyidce), Fungus-midges (Mycetophilidce), Chironomidce, 
Culicidce, and Tipididce], the Diptera that are gnatlike in shape 
and possess long antennae ; neither is the character found in the 
Bobber-flies (Asilidce), the Dolichopodida? (shining green, narrow- 
bodied, long-legged flies, usually found in the vicinity of water), nor 
