Numerous cases of this sort have come under my observation, but it often requires a profound knowledge of entomology to determine the species. Several examples of œstridean larvæ occur amongst them. For one example of _Œstrus hominis_ I am indebted to Mr Higginson, of Liverpool, who obligingly supplied me with notes of the case. Dr Kirk presented me with a small bot which he removed from Livingstone’s leg. I afterwards deposited the African bot, in his name, in the Hunterian collection. Bates speaks of an Œstrus in Brazil producing boils in human flesh. Westwood quotes similar instances. Of these, one was extracted from the thigh by Dr Brick. Mr Doubleday, the entomologist, extracted one from his own leg, and M. Goudot, another entomologist, was also victimised in the same way. Both of these _savans_ were travelling in America at the time. Two cases from South America were also recorded by Howship. In one the larva lodged in the back; in the other in the scrotum. Humboldt noticed that the Indians were much infested by Œstridæ. Three cases are severally recorded by Roulin, Guérin, and Audouin. Mr Stroop also mentions a case in which an Œstrus was removed from an ulcer on the shoulder of a boy in Texas. Another kind of bot known as the Macaco worm (_Cuterebra noxialis_) occasionally attacks man, but more frequently cattle and dogs. For one example, taken from the leg of a negro, at Belize, British Honduras, I am indebted to Dr Dobson (A. M. D., Netley). Hope’s list records five cases of bots of _Œstrus hominus_, one of _Œ. Guildingii_, one of _Œ. bovis_, and thirteen others (belonging to the same genus) as having been noticed in man. Since his time many additional cases have been recorded by J. M. Duncan and others. In like manner a legion of cases in which the maggots of various Muscidæ have been noticed, either in, upon, or from the human body. At a meeting of the American Academy in April, 1859, Dr Leidy showed some larvæ of the bluebottle fly vomited by a child; five larvæ of the flower-fly (Anthomyia) from a physician’s own person (which had produced choleraic symptoms); and nine examples of _Cuterebra noxialis_. I have myself encountered numerous insect larvæ in medical practice. Amongst others I have obtained the larvæ of _Anthomyia canalicularis_ in six or eight separate instances. One set of specimens, identified by Wunderlich, was sent to me by Dr Brandt, of Oporto. Drs Duffin, W. Fox, and Leared have supplied me with others. The larvæ described in Farre’s case, not being setose, must be referred to one or other of the Muscidæ proper. Mr Hope gave nearly forty cases of this kind, referable to eight different species of fly, and, as already implied, I have myself collected a great variety of the maggots of Muscidæ passed by the bowel, besides others obtained either from beneath the skin or from open ulcerations.