21 
observable with high magnifying powers, which may be described 
as a kind of flat transparent flap, with a bulb-like formation or 
appendage accompanying, covered with bristles.* The use of the 
hairy bristle does not appear to be quite known, though it seems 
likely that, as in the case of the (conjectural) use of the very similar 
appendage to the foot of the “Sheep Tick” or “Spider Fly” of the 
Sheep, it may be of service to enable the Fly to gain a firmer hold, 
by curling the bristle around a few hairs or pieces of wool. 
With regard to the “flap and bulb” structure, I believe not 
only its use but its existence were unknown up to the date of my 
observations in 1895. But from the very peculiar structure of the 
sides of the “flap,” much resembling, to external observation, what 
are known as pseudo-trachea in the flexible lobes, known as labellne, 
which form the terminal portion of the proboscis of the Bluebottle 
Fly f ; also, from my own observations, that when the flies were 
confined in a card-board box with upright sides, no help was given 
by the claws to their ascent, but they simply progressed upwards 
by holding on with the basal part of the claws, the rest being thrown 
up apparently free from all attachment; from these circumstances 
I conjecture that the apparatus of the “ flap ” serves, by means of 
suction, as a kind of adhesive organ. This, however, I merely 
submit as a suggestion. 
For ordinary work, by the help of their strong file-sided claws 
and the elaborate structure of the foot, the flies have an extraordinary 
power of holding on to the hairs, and besides can run to and fro, 
backwards, forwards, or sideways with a kind of crab-like move¬ 
ment, amongst the hair, or on the tender parts of the skin which 
they most frequent, so as by pulling, scratching, and tickling to 
perfectly terrify animals unacquainted with the infestation. 
Horses unused to it become restive, and frequently unmanage¬ 
able, plunge and kick and strike with their feet, in their endeavours 
to rid themselves of the plague ; and the more high-bred and high- 
spirited the horse, and sensitive to foreign touch on the skin, the 
greater the annoyance and consequent risks. 
The parts most infested are those which are the most tender, 
and also those from which the animal has itself the most difficulty 
in removing the plague. Beneath the tail is the locality that is 
* For description of these and other appendages of the foot of the H. equina, 
see my Nineteenth Annual Eeport, with two plates accompanying of greatly 
magnified figures. 
f See figure, much magnified, given in ‘Our Household Insects,’ by Edw. A. 
Butler, B.A., B. Sc. Plate li. 
