_Eristalis_--The larvæ of _Eristalis_ are the so-called rat-tailed maggots, which develop in foul water. In a few instances these larvæ have been known to pass through the human alimentary canal uninjured. Hall and Muir (1913) report the case of a boy five years of age, who had been ailing for ten weeks and who was under treatment for indigestion and chronic constipation. For some time he had vomited everything he ate. On administration of a vermifuge he voided one of the rat-tailed maggots of _Eristalis_. He admitted having drunk water from a ditch full of all manner of rotting matter. It was doubtless through this that he became infested. It is worth noting that the above described symptoms may have been due to other organisms or substances in the filthy water. _Piophila casei_, the cheese-fly (fig. 99), deposits its eggs not only in old cheeses, but on ham, bacon, and other fats. The larvæ (fig. 98) are the well-known cheese skippers, which sometimes occur in great abundance on certain kinds of cheese. Indeed, some people have a comfortable theory that such infested cheese is especially good. Such being the case, it is small wonder that this species has been repeatedly reported as causing intestinal myasis. Thebault (1901) describes the case of a girl who, shortly after consuming a large piece of badly infested cheese, became ill and experienced severe pains in the region of the navel. Later these extended through the entire alimentary canal, the excrement was mixed with blood and she suffered from vertigo and severe headaches. During the four following days the girl felt no change, although the excretion of the blood gradually diminished and stopped. On the fourth day she voided two half-digested larvæ and, later, seven or eight, of which two were alive and moving. That these symptoms may be directly attributed to the larvæ, or "skippers," has been abundantly shown by experimental evidence. Portschinsky cites the case of a dog fed on cheese containing the larvæ. The animal suffered much pain and its excrement contained blood. On _post mortem_ it was found that the small intestine throughout almost its entire length was marked by bloody bruises. The papillæ on these places were destroyed, although the walls were not entirely perforated. In the appendix were found two or three dead larvæ. Alessandri (1910) has likewise shown that the larvæ cause intestinal lesions. According to Graham-Smith, Austen (1912) has recorded a case of myasis of the nose, attended with a profuse watery discharge of several weeks duration and pain, due to the larvæ of _Piophila casei_.