'(122) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 363 



to this with interesting results. He submitted M. domes- 

 tica for five hours to a temperature of - 1*5 C., and they 

 continued to move. Exposed for eight hours to a temperature 

 of first - 3 C. and then - 2 C. they moved their legs. On 

 being submitted for twelve hours to a temperature first of 

 3'7 C. and then 6'3 C., they appeared to be dead, but 

 on being warmed they recovered. When exposed for three 

 hours to a temperature of 10 C. which was then raised 

 to 6 C., they died. These experiments show that M. 

 domestica is able to withstand a comparatively low degree 

 of temperature. 



Light. The female of M. domestica deposits the eggs 

 in dark crevices of the substance chosen for the larval nidus 

 and as far away from the light as possible. Beclard (1858) 

 showed that the eggs develop more quickly under blue and 

 violet glass than under red, yellow, green, or white. The 

 larvse are negatively heliotropic, as Loeb (1890) has also 

 proved in the larvae of the blow-fly. As I have previously 

 shown, the distinction between light and darkness is probably 

 appreciated by the larvas by means of the sensory tubercles 

 of the oral lobes. 



2. Hibernation. 



This question is intimately connected with the preceding 

 physiological facts. The disappearance of the flies towards 

 the end of October and in November is a well-known fact, 

 and an endeavour to discover the reason for this has been 

 made in the present investigation. 



I have found that the majority of flies observed were killed 

 off by the fungus Empusa muscae Cohn which is described 

 in the present paper. Of the remainder some hibernate and 

 some die naturally. This natural death may be compared, 

 I think, to the like phenomenon that occurs in the case of 

 the hive-bee Apis mellifica, where many of the workers 

 die at the end of the season by reason of the fact that they 

 are simply worn out, their function having been fulfilled. 

 The flies which die naturally have probably lived for many 



