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makes use of this long instrument to thrust the egg down to the sur- 
face of the skin, which she does not pierce, but only glues its eggs to 
it, the young larvee when hatched burrowing into the flesh. If this 
be the case, the act of oviposition must be unattended with pain, as in 
the case of the deposition of the eggs of @strus Equi, and we must 
search for the cause of the alarm of the herd, either in an instinctive 
knowledge that a certain insect flying around them is the parent of a 
grub which at a future time will be a torment to them, or in the attacks 
of some other insect ; and I confess that I am inclined to consider that 
Virgil’s beautiful description of the annoyance caused by 
“ Myriads of insects fluttering in the gloom, 
(Gstrus in Greece, Asilus named at Rome,) 
Fierce and of cruel hum ”’— 
has a Tabanus rather than an (strus for its origin. 
The larva of the Estrus Equi resides beneath the skin of the back 
of the ox, causing large tumours, and having the extremity of its 
body constantly placed at the orifice of the wound, where it was in- 
troduced as an egg, or introduced itself as a grub, the openings of its 
respiratory apparatus being placed at that part of the body. 
These introductory remarks on the different modes in which insects 
attack our horses and oxen, and the different effects which they pro- 
duce, will enable us the better to estimate the effects produced by an 
insect, or several species of insects, of tropical Africa upon the horses 
of travellers who have lately returned from that part of the world, 
where their enterprising researches have been rewarded by the disco- 
very of the great central lake Tchad. Captain Frank Vardon, a gen- 
tleman who has travelled far in the interior of Africa, has placed in 
my hands some fragments of Dipterous insects which attacked his 
horses, causing the death of one of them. The following is an ex- 
tract from his note to me in reply to my inquiry as to the mode of 
its attack :— 
“33 Oxford Terrace, Hyde Park, May 1850. 
“Dear Str,—I had always heard that the fly of South Africa so 
destructive to cattle was a large gad-fly, the size of a bee or hornet. 
This is quite erroneous: it is not very much larger than the common 
house-fly, but a longer and more ‘rakish’-looking insect, and easily 
distinguished by the transverse black bars on its body. 
“<1 fancy it is not met with south of the Tropic of Capricorn. It 
is usually found on hills, plains being free from it. I have ridden 
up a hill and found the Sétsé increasing at every step, till at last forty 
or fifty would be on my horse at once. The specimens you saw cost 
me one of the best in my stud. He was stung by some ten or a dozen 
of them, and died m twenty days. I myself have been bitten by the 
Sétsé ; you would almost fancy it was a flea biting you. Some parts 
of South Africa are, I should say, rendered inaccessible by the presence 
of this pest ; I mean of course to a man who travels in the usual way, 
with his oxen and horses. 
** How far the Sétsé extends in the interior is of course as yet un- 
known, but I have certain information as to its being 200 miles north 
