48 VETERINARY PARASITOLOGY 
The larva is only 9 to 10 millimetres in length. It 
has no spines and no oval hooks, and the skin is very 
thin and transparent. 
The tumours usually arise under parts which are 
commonly covered by harness, 
_, such as the neck, withers, and 
7 back. 
Curative treatment may be 
applied, as in the ox. 
Gstrus Ovis is a small 
greyish-coloured fly, 10 to 12 
millimetres in length. Thorax 
brownish-grey, streaked with 
dark obscure lines; abdomen 
slightly hairy, marbled with 
yellow, black, and white. The 
wings carry at their bases three 
black spots. 
The fly is active from May to October. 
The larve enter the nasal cavities of sheep, and finally 
reach the sinuses and horn-cores. They will be discussed 
more fully later. 
Fic. to.— Cistrus Equi. 
4. Hippoboscide, or Pupipara. 
The female deposits the nymph. 
There are two species of importance : 
I. Hippobosca Equina (the Spider-Fly).—This fly 
attacks the soft parts of the skin of the horse, or even 
ox or dog, especially around the anus, eyes, and groin. 
It does not puncture the skin, but merely irritates. It 
is only 8 millimetres in length. 
It is a very obstinate insect, and can only with 
difficulty be driven away. It causes great stamp- 
ing and kicking among animals with fine sensitive 
skins. 
Hippobosca rubipes is a native of South Africa, and is 
