THE DIPT ERA. 
405 
mentary trunk. When in the imago or perfect condition they do 
not take any nourishment ; but inasmuch as they chase horses, 
oxen, and sheep, and all kinds of ruminants, and frighten them 
with their buzzing, they are generally supposed to sting the ani- 
mals, but really they are incapable of doing anything of the kind. 
The Gad Flies, or Tabani , chase the animals in order to suck 
their blood, but the bot flies seek them in order to lay their eggs, 
for their larvae live as parasites upon the domestic animals, and 
ruminating Mammalia generally. The adult fly lays its eggs on 
the skin of some particular animal, and in some instances they 
are licked off the skin and are conveyed into the stomach, where 
they hatch, and the larvae live by sucking the juices of the 
animal or the matter which their presence produces. Some 
larvae are hatched on the surface of the skin, and they then 
bore into the body underneath, and feed there. The larvae 
are thick, fleshy bots, without feet, and they are covered with 
rows of spines and tubercles, by which they move about, and 
they breathe through spiracles, which open at the end of the 
body. They moult twice, and just before attaining the pupa 
state they leave the bodies of the creatures they have lived in, 
and reach the ground, where they undergo their metamorphoses, 
the pupa being protected by the dried skin of the larva. The 
bot fly of the horse buzzes about horses and lays its eggs 
rapidly, and attaches them with a sticky substance to the hair 
about those parts of the body which the animal is in the habit 
of licking. The eggs are hatched, and the horse swallows the 
larvae and they pass down into the stomach, to which they become 
fixed by means of their hooked mandibles. After a certain time 
they are passed out with the excrement and undergo their 
metamorphoses in cracks under the ground. The bot which 
affects sheep is an object of great terror to them. It lives in 
its larval state up the passages which lead from the nose amongst 
the front bones of the head, and produces much suffering. The 
larvae of some bots, especially those which attack oxen, deer, 
and goats, dig themselves under the skin of those animals, and 
produce little tumours ; and this is well known to some birds, 
for the starlings may be constantly seen at certain seasons of the 
year looking out for them on the backs and flanks of deer. 
