74 
HOW TO COLLECT 
order to minimize the damage should a disc happen to get loose 
The box containing the specimens should be well wrapped in cotton- 
wool or similar material, and firmly packed in an outer case for 
transmission (by parcel-post if possible and the package is not too 
large) to England. 
Number of Specimens of each Species required. 
At least half a dozen specimens of each sex of a species should, if 
possible, always be obtained, and a good look-out should be kept for 
specimens showing any abnormality in structure, coloration, or 
size. When the collector remains long enough in one spot, he should 
always endeavour to obtain specimens of a species on different dates, 
in such a way as to throw as much light as possible on the duration 
of its seasonal occurrence. Similarly the attempt should be made to 
illustrate the geographical range or local distribution of a species, 
by collecting specimens in as many different localities as possible. 
Specimens of species taken in new localities, though common else- 
where, will always be valuable. 
Larvae and their Habits. 
The habits of Dipterous larvae are as varied as the outward 
appearance of the larvae themselves. The latter may be met with 
almost everywhere, but especially in decaying matter of all kinds, 
in water both running and stagnant, in the ground, attacking the 
roots and bulbs of plants, or mining in the stems and leaves. It is 
worth noting, especially as a means of distinction from Coleopterous 
larvae, that no Dipterous larva is possessed of true {thoracic) legs, 
though in many species (e.g. Eristalis, Helophilus) prolegs or trans- 
verse ridges having a similar function are distinctly visible. 
The following notes as to the mode of life of the larvae of some of 
the best-known families of Diptera may be useful : — 
The tiny pink- or scarlet-coloured grubs of the Gall-midges 
(Cecidomyidce), as their name implies, form galls on the leaves and 
stems of plants. 
