ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 215 



the flies of subsequent generations only live a few days, and never reach 

 sexual maturity. 



The estimations of the multiplication of flies during the fly season 

 are much exaggerated. Among blow-flies confined in large open cages 

 and protected from many enemies and certain adverse conditions, the 

 descendants of each female only numbered 180 individuals. Amongst 

 " wild " flies the increase must be considerably smaller. The normal 

 duration of life among blow-flies is about thirty days in the summer. 

 A considerable mortality often follows cold, wet, and windy days. 

 Oppressive sultry weather is productive of the greatest mortality. Flies 

 die if exposed to very hot sunshine. 



During the season many difl^erent flies enter rooms, most by accident, 

 but C. erythrocephala, Stomoxys calcitrans, F. canicularis, and M. domestica 

 by intention. The different species vary in their occurrence at different 

 seasons. Those that require a high " critical " temperature for emerging 

 from pupse appear late and disappear early. The disappearance of flies 

 in autumn is not due to the effect of cold on the adults, but to the non- 

 emergence of flies from pupse. The conditions limiting numbers 

 include the destruction of larvae and pupse by Braconid and Chalcid 

 parasites and other enemies, lack of food for the larvae, the appetite of 

 other species of larvae, the enemies of the adults, and the weather. 

 Baited traps in the open catch many flies ; dark or shaded receptacles 

 catch few. Only about 16 p.c. of the flies that visit human excre- 

 ment and decaying animal matter are males ; they seldom venture 

 into dark receptacles. All the species of flies that visit excrement and 

 decaying animal matter also visit fruit. There is great contamination 

 of fruit (on trees and exposed for sale) with fsecal and putrefactive 

 bacteria carried by flies and wasps. 



The activities of flies are most affected by temperature. The larvae 

 of Hydrotxa dentipes devour other fly larvae. Burial of dead animals 

 does not prevent the development of the larvae present on them, nor 

 the emergence of the flies. It is probable that wasps act not infrequently 

 as agents in disseminating pathogenic and putrefactive bacteria. 

 Contact with infected adults of M. domestica is not essential in the 

 transmission of Empusa disease. The house-fly may be infected by 

 C. erythrocephala, H. dentipes, and F. caniculaiHs which occasionally die 

 of the disease. 



Various mites attach themselves to flies for several days. They 

 may act as carriers of Nematodes. The Pseudo-scorpions {Ghelifer 

 nodosus and C. scorpioides) sometimes occur on flies for several days. 

 Braconid larvse pass the winter in fly puparia, and so do some Chalcids. 



Gynandromorphous Butterflies.* — E. A. Cockayne discusses gynan- 

 dromorphism in Agriades coridon, ab. roysto?imsis. There is some 

 evidence that it runs in families at Royston on the borders of Hertford- 

 shire and Cambridgeshire. Careful dissection was made of twenty-five 

 undoubted cases, and the peculiarities of the genital system (always 

 female internally and externally) are described. As regards external 



* Trans. Entomol. Soc, London, 1916, pp. 213-63 (9 pis. and 9 figs.). 



