366 DIPTERA. 



In the second group, the Diptera cydorapha, the true coarc- 

 tate, cylindrical, smooth puparium is ibrruecl by the contraction 

 of the larva skin, but is very different in shape from the ma- 

 ture larva ; while this puparium remains in vital connection by 

 means of tracheae, with the enclosed pupa, which escapes from 

 the puparium through a curved seam or lid in the anterior 

 end, and not by a slit in the back. This group includes the 

 PipunculiddB , Syrphidm, Conopidce, (Estridai, Mus- 

 cidce and Pupipara. 



Certain Diptera are injurious to crops, as gall producers, but 

 indirectly the Tacliinidce, are beneficial since they prey on cat- 

 erpillars ; while the greater number act as scavengers in the 

 water and on laud, and thus as sanitary agents. Diptera enjoy 

 a wider geographical range than other insects. Kone of the 

 larger families are exclusively tropical; the Muscidce and 

 mosquitoes are found in the circumpolar regions in abundance, 

 as well as in the tropics. They are the earliest to appear in 

 spring and the latest to disappear in autumn. They are 

 active at all times, in rain or sunshine, clay or night, though 

 the greater number prefer the sunshine. 



From their habit of living in vegetables, flowers, and other 

 substances sometimes eaten by persons, physicians occasion- 

 ally are called to treat cases where dipterous larvae have been 

 swallowed and produced sickness. Among those most fre- 

 quently vomited are larvae of various jMuscids, especially An- 

 thomyia. " C. Gerhard t records a case in which a patient, after 

 four days illness, vomited about fifty larvae of some dipterous 

 insect, probably a large species of Muscidae. A. Laboul- 

 bene describes and figures in the Annals of the Entomologi- 

 cal Society of France, a larva of Trichomyza fusca Macquart, 

 which is exceedingly abundant in the public urinals in France, 

 and which lives in human urine. He identities it with the 

 larvae described and figured by Davaine in 1857, as having been 

 evacuated from the intestines of a woman after she had suffered 

 much pain. (Zoological Record for 1867.) Four other cases 

 are on record of larvae having been voided by the urinary pas- 

 sages, or found living in urine, though, as suggested to us by 

 Dr. Hagen, it is possible that in such cases, the worms were 

 not voided, but lived in the urine previous to the time they 

 were detected by the reporters of such cases. 



