DIPTERA. 367 



Dr. J. Leidy reports in the Proceedings of the Academy of 

 Natural Sciences of Philadelphia, for 1859, a case where a num- 

 ber of specimens which "appeared to be the larvae of the Blue- 

 bottle fly," were given him by a physician, having been vomi- 

 ited from the stomach by a child. Also, a second case where 

 numerous larvse of a species of Anthomyia, " were given to him 

 for examination by a phj'sician who had obtained them from 

 his own person. He had been seized with all the symptoms 

 of cholera morbus, and in the discharges he had detected nu- 

 merous specimens of this, to him, unknown parasite. It was 

 in the latter part of summer, and the larva, it is suspected, 

 had been swallowed with some cold boiled vegetables. Dr. 

 Leidy had observed the same kind of larva in another case, 

 accompanied with the ordinary phenomena of cholera mor- 

 bus." 



Isidore Geoffroy Saint Hilaire records a case of a larva of 

 the common fly found living in the skin of an infant ; while 

 Dr. Livingston, according to Cobbold, detected a "solitary 

 larva of a species Avhich had taken up its residence in his leg. 

 Dr. Kirk removed this parasite by incision ; and on a second 

 occasion he obtained a similar specimen from the shoulder of 

 a negro." 



There are about 2,500 species of North American flies de- 

 scribed, and it is probable tliat the number of living North 

 American species amounts to 10,000. In Europe there are also 

 about 10,000 known species, belonging to about 680 genera. 



The flies of this countr}', compared with the other groups, 

 have been but little studied, though the habits of many are so 

 interesting and the species very numerous. The diflferent parts 

 of the body vary much more than in the Hymenoptera and 

 Lepidoptera, and in such a degree as to often afford compara- 

 tively easy characters for discriminating the genera. 



Their habits are very variable. Fresh water aquaria are 

 necessary for the maintenance of aquatic larva. If quantities 

 of swamp mud and moss with decaj-ing matter are kept in boxes 

 and jars, multitudes of small flies will be hatched out. Leaf- 

 mining and seed-inhabiting species can be treated as micro- 

 lepidoptera, and earth-inhabiting larvie like ordinary cater- 

 pillars. Dung, mould in hollow trees, stems of plants and 



