3B6 DIPTERA. 



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

 tate, cylindrical, smooth puparium is formed 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 trachea?, with the enclosed pupa, which escapes from 

 the puparium through a curved seam or lid in the anterior 

 end, and not l)y a slit in the back. This group includes the 

 Pipuncalida; , SyrphidcK, Conopidoi, (E stridoe^ Mus- 

 cidce and Pup ip a r a . 



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

 indirectly the Tachinidai are beneficial since the}- prey on cat- 

 erpillars ; wiiile the greater number act as scavengers in the 

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

 a wider geographical range than other insects. None of the 

 larger families are exclusively tropical; the 3Inscidoi 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, day 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 larvte have been 

 swallowed and produced sickness. Among those most fre- 

 quently vomited are larvas of various Muscids, especially An- 

 thomj'ia. " C. Gerhardt 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 Teichomyza fusca Macquart, 

 which is exceedingly abundant in the public urinals in France, 

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

 larvae described and figured b}' 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 urinar}^ pas- 

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

 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. 



