These oestri especially attack herbivorous mammals, and the terms _gastricola_, _cuticola_, and _cavicola_, sufficiently indicate the places which they inhabit; the first kind lodging in the stomach, the second frequenting the skin, and the third establishing themselves in some of the cavities of the body. Dr. Livingstone doubtless alludes to some kinds of oestri when he mentioned the numerous intestinal worms which infest animals in Southern Africa: "All the wild animals," says the celebrated traveller, "are subject to intestinal worms. I have observed bunches of a tape-like thread-worm and short worms of enlarged sizes in the rhinoceros. The zebras and elephants are seldom without them, and a thread-worm may often be seen under the peritoneum of these animals. Short red larvæ, which convey a stinging sensation to the hand, are seen clustering round the trachea of this animal, at the back of the throat; others are seen in the frontal sinus of antelopes; and curious flat leech-like worms are found in the stomachs of leches" (a new species of antelope).[4] A species, peculiar to the horse in Europe, usually lives in its 174 stomach in summer; and when its development is complete, the winged insect follows the course of the food, and goes out from the anus to breathe the open air. The mother fly, excited by the sentiment of maternity, flies round the breast of the first horse that she meets, and lays her eggs there on some hairs which are not beyond reach of the animal's tongue. The horse wishing to get rid of these foreign bodies, licks them off, and thus they are introduced into the mouth, and from the tongue pass to the stomach. These eggs are hatched in the midst of the gastric juice, the larvæ leave them, and the young gadflies find in the juices of the stomach the milk which serves to nourish them. These larvæ pass through their metamorphoses in the stomach, and when the young fly has assumed its perfect form, with its delicate wings, its sucker, and its facetted eyes, it leaves the stomach, follows the path traced by the food, arrives some fine day at the rectum, presents itself at the place of exit, and takes its flight. Thus the fly can take its journey through the intestines on a portion of the digested food. When she has once taken her flight she is very near the end of her life, and after a moment of love she gives up her place to others. There is another gadfly which finds a _crèche_ in the sheep; but instead of lodging in its stomach, it instals itself in the nostrils, which are more easily reached. This second species goes through its evolutions in the vestibule. This is the species which sometimes introduces itself into the body of man. Many instances of this have been known, and our late colleague Spring gave a very interesting account of one of them in the 175 bulletins of the Belgian Academy.