144 



emerge as soon as the temperature approaches the critical point. 

 On the other hand, on many warm days no emergence whatever took 

 place. 



Data were obtained on the rate of multiplication of blow-fiies. 

 The number of descendants of each female kept under open-air con- 

 ditions, and protected as far as possible from enemies, was about 130 

 during the season. Under natural conditions it may be assumed that 

 this number is still smaller. The average duration of the life-cycle in 

 summer during these experiments was 30 days. The low rate of 

 increase observed, as compared with the theoretical rate discussed by 

 Howard, seemed to be almost entirely due to a high mortality occurring 

 among newly emerged flies of generations subsequent to the winter 

 one, individuals of Avhich showed great powers of endurance. No 

 definite conclusions can yet be drawn as to the cause of the mortality 

 observed, but it was found that the death of many flies occurred after 

 wet, cold and windy days and of still more in hot weather, or as a 

 result of direct exposure to the sun. 



Records were made during the seasons of 1914 and 1915 of the species 

 entering rooms. The following were observed : — Psychodidae, 

 Syrphidae, Platystoma seminationis, Tephrochlamys canescens, Blepha- 

 roj)tera serrata, Scatopliaga stercoraria, Fannia manicata, F. armata, 

 F. scalaris, Azelaria macquarti, Hydroiaea irritans, Anthomyia 

 pluvialis, Digonochaeta spinipennis, Microchrysa polita, Sargus cup- 

 rarius, S. iridatus, Thereva pleheia, Lonchaea vaginalis, Helomyza olens, 

 Mijdaea urbana, M. obscurata, M. meditabunda, M. impyuncta, 

 M. tdigtnosa, Coenosia iigrina, Pegomyia bicolor, Phaonia variegata, 

 P. erratica, Chortop)hila fugax, Graphomyia maculata, Musca autumnalis 

 (corvina), Brachycoma devia, Phryxe vulgaris and Voria ruralis. The 

 majority of these enter houses accidentally, but C. erythrocephala, 

 S. calcitrans, F. canicularis, and M. domestica do so for a definite 

 purpose. C. erythrocephala is attracted by food on which to oviposit. 

 S. calcitrans enters for shelter and may occasionally attack persons in 

 the room. F. canicidaris is numerous throughout the season, but it is 

 probable that the individuals do not remain long indoors. M. domestica 

 enters houses persistently and remains indoors until ready to oviposit. 

 The first six individuals of M. domestica observed to enter a room 

 appeared in 1915 on 6th June, five of which were males. All were newly 

 emerged, a fact which supports the view that the wdnter is passed in the 

 pupal stage. Between June and September the captures in the same 

 room included 60 per cent, males, while in October 60 per cent, were 

 females. During this month the flies tended to remain in the room for 

 much longer periods. House-flies kept outside in cages laid few eggs, 

 the temperature conditions being apparently unfavourable. No eggs 

 were ever found to be deposited on food in kitchens. 



Observations on the habits of various flies under natural conditions 

 showed that the form and situation of the traps, the baits used, the 

 weather conditions,and the season of the year, all influenced the number 

 and species of flies captured. The traps, which were of the mosquito- 

 net and galvanised iron types, were placed in difterent positions and 

 were baited wdth human excrement, decaying animal matter, or fruit. 

 Traps in the open, baited with excrement or decomposing animal 

 matter, attracted 39"5 per cent, and 37'6 per cent, respectively of the 

 total number caught ; dark receptacles in open situations caught 



