HOW TO COLLECT DIPTERA (TWO-WINGED ELIES). 65 
To support the discs No. 16 should be used ; but, if these cannot 
be obtained, common pins may be employed. 
Gun-wacl punches, Nos. 4, 12, and 20 bores (from any gun-maker), 
for punching discs of card. 
Cards (3- or 4-sheet Bristol board), from which to punch discs ; a 
supply of the latter should be prepared ready for use. 
A platyscopic lens (Messrs. Baker, 244, High Holborn, London, 
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 Boad, London, 
S.W.) 
Two or three cork-lined entomological store-boxes. —These can be 
obtained from Messrs. Watkins A Doncaster, 36, Strand, London, 
W.C., 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 DlPTEBA FKOM OTHER INSECTS. 
Disregarding a few abnormal wingless forms, Diptera may be 
distinguished from all other insects by the fact that they possess 
only one pair of wings, and are without caudal filaments. 1 hus, 
besides ordinary flies, such as Blue-bottles and House-flies ( Muscidee ), 
the Order also includes Midges ( Chironomida'), Gnats or Mosquitoes 
(Culicidce), Daddy-long-legs ( Tipulidie ), 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 foie- 
