(60) 



500 C. GOEDON HEWITT. 



which were mixed, when in a rotting condition, with earth to 

 make a more solid mass. Although they can be reared in 

 such food-stuffs as bread soaked in milk and boiled egg, when 

 these are kept at a temperature of about 25 C., I was unable 

 to rear them to maturity in cheese, although they fed on the 

 substances for a few days and then gradually died, my failure 

 may have been due to the nature of the cheese which was 

 used, only one kind being tried. In addition to rearing the 

 Iarv88 on isolated human faeces, such as are frequently found 

 in insanitary court-yards and similar places, they were found 

 in privy middens, and also on a public tip among the warm 

 ashes and clinker where the contents of some privy middens 

 had also evidently been emptied ; I bred the flies out from 

 this material. 



III. FACTORS OF DEVELOPMENT. 



The rate of development depends primarily on the tempera- 

 ture of the substance on which the larvae are feeding. This 

 was shown in my experiments in which the larvae were reared 

 in horse-manure kept in a moist condition in an incubator at 

 a constant temperature of 35 C. At this temperature the 

 development is completed in eight to nine days. I found that 

 a higher temperature of 40 C. was too great for the larvae as 

 they were simply cooked and perished at such a temperature. 

 This has been confirmed by Griffith (I.e.), who found that 

 the life-history was completed in the same time on incubating 

 at a temperature of about 22 23 C. I do not think that a 

 shorter time than this for the development that is, from the 

 deposition of the egg to the emergence of the perfect insect 

 from the pupae will ever occur in this country, as we rarely 

 enjoy prolonged spells of hot weather which would bring 

 about such conditions as regards temperature. It is interest- 

 ing to note that Smith (1907) gives the time of development 

 in horse-manure in India under natural conditions as eight 

 days; he also bred M. domestica from an artificial latrine 

 containing human excreta mixed with earth, which confirms 



