144 INSECTS DIPTEBA DIAGRAM G, 



making a cocoon, or changing their skin. At the end of about 

 eleven days, the fly emerges from the chrysalis. 



The old skin of the larva splits at one end, as if it could not 

 contain the /inimal within it. The fly when ready to emerge, 

 swells its head, which makes the chrysalis split ; it swells itself 

 again to get rid of the covering which surrounds it ; and at last 

 it stands on its legs ; but it is pale in colour, its wings are soft, 

 and it cannot fly, and remains quiet in one place. But in a few 

 minutes its wings have dried, its skin has become dark, and it 

 flies away. 



The oestrus is a fly the larva of which has very singular habits. 



The fly lays its eggs on living 

 animals, horses, oxen, or 

 sheep. As soon as the larva} 

 are hatched, they bury them- 

 selves under the skin, where 

 they remain, and sometimes 

 CEstrus. Larva of oestrus, form a small tumour in which 



the larvse are found when they are opened ; they only leave it 

 when they are about to go into the pupa state, when they fall on 

 the ground, and there undergo their last metamorphosis. 



But some cestri lay their eggs on the fore legs of the horse, 

 where he can reach them with his tongue. When he begins to 

 feel a little pain there, he licks the spot, and swallows the young 

 larvae. Their strong outer skin cannot be digested by the 

 gastric juice, and therefore the larva does not die. It attaches 

 itself to the surface of the stomach, and continues to live there 

 until the time for its first metamorphosis, when it drops into the 

 food, and is expelled from the body, when it becomes a fly at the 

 end of a certain time. 



The gadfly, instead of having a proboscis like the flies has a 

 sucker like the gnats. It pierces horses to feed on their blood, 

 but always makes a large wound from which it flows in 

 abundance. The gadfly also attacks man ; its puncture is not 

 dangerous, but it may communicate either to animals or to man 



