Descriptions of British Diptera. 361 
heat of the day, and are therefore most troublesome to cattle and 
beasts of burden where they stand most in need of repose. They 
are particularly excited and eager for blood when the atmosphere is 
in a warm and humid state, such as it usually is after a thunder 
shower. It is invariably observed to be the females that attack 
animals, the males being usually found on flowers from which they 
extract the juices ; * both sexes, indeed, have been known to feed 
on a saccharine liquid. The quantity of blood which they can gorge 
is much more considerable than might be supposed from the size of 
the body, as the latter, after a full meal, becomes dilated beyond 
its usual dimensions. Several of them attack indiscriminately many 
different kinds of the larger quadrupeds, especially the ruminants, 
but others, like the (Estri, more particularly attach themselves to 
certain species. Thus, the rein-deer has a winged parasite appro- 
priated almost exclusively to itself; and it is not improbable that 
a more extensive knowledge of the history of these flies would make 
us acquainted with others equally restricted in the choice of their 
victims. 
The oral organs of the Tabani are very highly developed, consti- 
tuting an apparatus for extracting the blood, of a somewhat com- 
plex structure, but admirably adapted to the purpose. It resembles 
a case of lancets, having all the parts so formed and adjusted to 
each other, that they serve at the same time to pierce the skin, and 
to form a tube for the passage of the fluid. Although so dissimilar 
in shape, these parts are found to correspond in number and situa- 
tion to the oral appendages of the Coleoptera. The concave lobes 
of the lip probably enable the insect to attach itself firmly, and to 
render the apparatus steady ; while the palpi are useful in divid- 
ing the hair, and form a kind of protecting sheath for the other 
parts when they are unemployed. In substance the pieces are so 
stiff and horny, that they easily make their way through the hard- 
est and coarsest hide. 
These insects deposit their eggs in the earth.fi The larva of one 
of the species, ( T. bovinus} has been figured and minutely described 
by De Geer. It is long, cy- 
lindrical, and rather slender, 
narrowing at the head into 
an elongated cone, and bear- 
ing much resemblance to those 
of some of the larger Tipuli- 
dse which live in the earth. 
* The same fact has been noticed in relation to the respective sexes'of va- 
rious Culices, and some other sanguisugous species. 
