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 STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 413 



one of the colleges (Cambridge), and were transferred to a 

 small experimental greenhouse in the laboratory where the 

 temperature was from 65 F. in the morning to 75 F. in the 

 evening. The flies were allowed to oviposit in moist bread in 

 which the process of fermentation had begun. He found 

 that the times for the developmental stages approxi- 

 mately agreed with those obtained by me at about the same 

 temperature, and that the whole development was completed in 

 about three weeks. At an average temperature of 70 F. the 

 eggs were all hatched in twenty-four hours. The first larval 

 stage lasted thirty-six hours, the second larval stage four 

 days, and the third stage was complete in five and a half 

 days; the whole larval period, therefore, occupied eleven 

 days. The average period occupied in the pupal stage was 

 ten days; some pupae incubated at a temperature of 77 F. 

 hatched in three days. 



It may be stated now, therefore, without fear of contra- 

 diction, that flies are able to breed during the winter months, 

 if the necessary conditions of food, temperature, and moisture 

 are present. It is probably from these winter flies that the 

 early summer flies are produced, as I have previously sug- 

 gested. 



CORRIGENDUM. 



My attention has been very kindly called by Prof. W. A. 

 Riley to a slight mistake that I have made in my account of 

 the venation of the wing (Part I, p. 412). By an oversight 

 I have termed transverse nervures the two small veins 

 m.cu. (medio-cubital) and cu.a. (cubito-anal). These are 

 really parts of the original longitudinal veins M. 3 and Cu. 2. 

 A study of such a series of dipterous wings as those figured 

 by Comstock in the papers there quoted (Comstock and 

 Needham, 1898), or in his ' Manual for the Study of Ento- 

 mology/ will show that these apparent transverse or cross- 

 veins are morphologically equivalent to branches of the 

 primary veins. 



THE UNIVERSITY ; 



MANCHESTER. 



