oy ixniAy parasitic flies. 
717 
do not follow them. This terror is attributed to a shrill buzzing, 
made by the fly. The flies certainly neither bite nor sting the cattel. 
The female has no instrument, as many parasitic flies have, capable 
of inserting an egg under the host’s skin. Her ovipositor is a flexible 
tube which opens and shuts in the manner of a telescope. 
The flies move with such extreme rapidity that they are difficult to- 
follow with the eye. They are rare in collections. The evidence seems 
to show that it is through the mouth of the host that the parasites 
reach the warbles, or subcutaneous tumours, in which they go through 
the last stages of their larval development. The female is so quick 
in performing the act of laying that she does not seem to remain on 
the host for more than a few seconds. The eggs are longish, flattened, 
white, with an appendage at the base which is perfectly adapted for 
clasping a hair. A number are often placed on a single hair. The 
appendage consists of two lobes, which form a bulbous enlargement 
at the base of the egg, and are attached to it by a thin neck. The 
lobes close over the hair and give a secure hold as soon as the egg is 
deposited. The eggs are laid on the backs and flanks of the cattle, 
perhaps on any spot which the beast’s tongue can reach. 
Once the eggs are laid, three possible courses have been put forward 
by different entomologists for the life-history of the parasite between 
the egg and the warble stage. First, that on hatching the larva eats 
its way through the hide and wanders a short distance in the sub- 
cutaneous tissues ; eventually it returns to the surface and gives 
rise to the well-known tumours, in which it lives until the time for 
pupation arrives. Or, secondly, having bored a way through the 
skin, the larva wanders extensively in the tissues of its host, sometimes 
reaching the spinal canal and the walls of the cesophagus. Even- 
- tually it returns to the surface and completes its development beneath 
the skin. Or, thirdly, that the larvse never bore through the skin of 
the host, but are taken into the throat when the beast licks the eggs 
off its body. Having hatched, the larva slowly bores through the 
walls of the cesophagus and wanders about the tissues, sometimes 
reaching the spinal canal through the spaces between the verte- 
brae. Eventually it reaches the skin as before. 
There are grounds for believing that the last is the normal life- 
history. During the early part of the larval life, growth would seem 
to be very slow, but the small parasite may wander far and wide 
through the host’s tissues. This is the winter period. Brauer called, 
this stage the Stillstandstadium, and pointed out that a similar period 
of slow growth occurred in other larvae of the CEstrid family*. 
AVhen the eggs are laid, the young larva; within are already well 
developed. Sometimes they are licked up with the hair attached 
and the larva inside, at other times they may have already hatched^ 
* “ Ueber das sogenannte Stillstandstadium in der Entwicbeliing dtr Oestiidcn 
Larven,” by F. Brauer (1892), TerJiandl. Zool-Boi. Gcscllschaft vol. 42 p. 79. 
