called Oistros by the Ancients. 409 
same time; and that the egg being hatched, the young grub 
insinuates itself into, and finally through the skin, forming an 
abscess beneath it. In a somewhat similar manner it is that the 
ichneumon flies deposit their eggs on the sides of living cater- 
pillars of the Lepidoptera, and hatching, perforate their skins, 
and entering within, live on the parenchyma or pulp of their 
bodies till matured and fully grown, when they make their way 
out again and change to the chrysalis. 
I may also remark of the (stri, that they appear to be won- 
derfully kept from such an increase as would be fatal to the 
animals they feed upon, by the difficulties and imminent hazards 
they are exposed to in the act of depositing their eggs. The 
teeth of the horse must destroy, one should imagine, nine-tenths 
of the CE. Equi, hemorrhoidalis, and salutiferus. The GZstri seem 
however, in the hands of Providence, to make a double recom- 
pense for the sufferings they occasion; first, by keeping the 
animals on the alert during hot weather, when they would be 
often too idly disposed for their welfare; while the few larvæ 
which succeed in getting into their bodies, appear to benefit 
them by their local irritations, stimulating the stomach to a 
quicker digestion of their watery food, and diverting diseases by 
their counter irritations of the skin and frontal cavities,—thus 
producing the effect of issues or vesicatories, which are powerful 
remedies in relieving and in preventing diseases. 
I apprehend that I have now sufficiently shown that the 
Œstrus of the ancients could have been no Tabanus, and that 
it is clear Olivier, who appears to have originated this notion, 
and who was followed by Latreille, was mistaken. 
A very extensive enumeration of this genus is seen in a late 
ingenious publication, the Systematische Beschreibung of J. W. 
Meigen. It is however in some instances not correct; for on 
carefully examining the Œstrus lineatus of this writer, intro- 
3G 2 duced 
