620 
DIPTERA. 
Some two-winged flies deposit their eggs in the stems, 
buds, and leaves of plants, thereby producing large tumors 
or galls, wherein their young reside. Others lay their eggs 
in fruits, on the pulp of which their maggots live. These 
gall and fruit flies belong to a family called Ortalidians 
(Ortalididje), from a word signifying to flap or shake the 
wings ; for they keep their wings in motion nearly all the 
time, jerking them up and down, and twisting them round 
so that the thick outer edges often come together. Some 
' of them are in the habit of suddenly raising their wings 
perpendicularly above their backs, and running along a few 
steps with them spread like the tail of a peacock. These 
insects, together with several other groups of flies, differ from 
all the foregoing in many respects, although they agree with 
them in their transformations. The forehead is broad in 
both sexes ; their winglets are very small or entirely want- 
ing ; their powers of flight are feeble ; and they arc rarely 
found sporting on flowers in the sunshine, but seem generally 
to prefer shady and damp places. 
The wings of the Ortalidians are often beautifully varie- 
gated, striped, or spotted with shades of brown or black. 
The hind body in the female generally ends with a pointed 
tube, wherewith the eggs are deposited. The little white 
maggots often found in over-ripe whortleberries, raspberries, 
cherries, and other fruits, are the young of some of these 
insects. Swellings, or galls, as large as a walnut, are often 
seen on the stems of some of our native asters or starworts. 
They are caused by the punctures of a fly, which lays its 
eggs, singly, in the stem, when the latter is tender. The 
puncture is followed by a spongy swelling, wherein the 
maggot, hatched from the egg, lives, and passes through its 
transformations. The insect finally comes out in the fly 
state, through a small hole previously made in the gall by 
the maggot. This fly may be called the gall-fly of the star- 
wort ( Tephritis Aster in'). Its body is about one fifth of an 
inch long ; it is of a light yellowish-brown color, with paler 
