594 
DIPTERA. 
is the longitudinal striation of the whole body, but this is sometimes 
only very faintly marked. One Pusa species Gastroxides ater (PL LXII, 
fig. 4) lives in hollow trees. 
Some of the larvse have the power of emitting a sound, a tiny squeak 
or click, like the noise made by a small electric spark. It has been sup¬ 
posed (Paoli, Redia, 1907) that 
a curious structure known as 
“ Graber’s organ ” (fig. 387) 
is concerned either with the 
production or with the per¬ 
ception of such sounds ; this 
organ can be seen in the living 
larva as two or three pairs of 
small black dots under the 
skin, the number and arrange¬ 
ment varying to some extent 
in different species. The form 
of the tail, breathing tube, and 
tracheae are also helpful in dis¬ 
tinguishing the larvae, as are 
also the shape and number of 
the tubercles and the arrange¬ 
ment of the small bristles on 
the body-segments. 
The pupa is found in the earth ; it lies free of the larval skin, and has 
usually rings of bristles on the abdomen and some spines and tubercles 
on the head and thorax (fig. 388). The thoracic spiracle is rather large 
and roughly crescent-shaped. At Pusa there are apparently three broods 
of Tabanus yearly, flies emerging at the beginning and end of the hot 
weather (about February and June) and at the end of the rains (October). 
Hibernation takes place in the larval condition through the cold 
weather in all those species with which I am acquainted at Pusa. 
Some species are attacked by small Hymenopterous egg-parasites, 
(PI. LXII, fig. le.), which in the case of one species of Tabanus we have 
found in a considerable proportion of the eggs observed, though the flies 
were common in spite of this. No practical method of getting rid of the 
flies has ever yet been found, except clearing their breeding-places. Their 
Magnified about eight times. 
