that spread Disease. 3 1 



so in the case of house-flies, it is more practicable to attack the 

 next generation than the present generation, that is to say, to 

 prevent the development of the larvae rather than to attempt to 

 destroy the winged flies, and this can be done by taking measures 

 such that moist rubbish and stable manure are not allowed to 

 accumulate and serve as breeding places for the flies. 



A single female of the common house-fly lays from 120 to 150 

 eggs at a time, and may deposit five or six batches during its life ; 

 and since in very hot weather the entire life-cycle may be com- 

 pleted in about three weeks, it is easy to account for the enormous 

 swarms of flies sometimes seen. 



The attention of visitors is drawn to a pamphlet entitled " The 

 House-Fly as a Danger to Health," which can be purchased in the 

 Museum for a penny. 



Blow-flies are not included in the series exhibited, for although 

 they are flies that enter houses and settle on food, particularly 

 cold meat and fish, they are not dangerous in the same sense as 

 the common house-fly. They are not attracted to dung-heaps and 

 other exposed faecal matter, and they breed in flesh, such as the 

 carcase of a recently dead animal. Blow-flies are a nuisance 

 principally from their habit of laying their eggs in any cold joint 

 of meat to which they have access. The eggs soon develop into 

 maggots or gentles, and owing to the power which these larvae 

 have of liquifying the meat around them, the joint becomes putrid 

 much more rapidly than if it had not become " fly-blown." 



SHEEP BOT-FLY. 



In one of the two sloping-faced table-cases in the middle of 

 the floor of the Hall are shown a specimen of the bot-fly of the 

 sheep, Oestrus avis Linn., three larvae, and enlarged coloured 

 drawings ( x 6) of the larva, pupa and adult female. The larvae 

 or maggots of this fly live parasitically in the cavities in the front 

 part of the head of the sheep, and when about to become pupae, 

 escape from the nostrils and fall to the ground. After a time the 

 winged flies escape, and lay their eggs in the nostrils of sheep. 



In Algeria, especially in districts in which sheep are few and 

 the human population fairly dense, the sheep bot-fly attacks the 



