DIPTEEA. 63 



heads and necks extended, their tails trembling, and held in 

 a line with the body, to rush to the nearest river or pond, while 

 such as are not attacked disperse. It is asserted that the buzzing 

 alone of the CEstrus terrifies a bullock to such an extent as to 





Fig. 45. Bot-fly (Oestrus bmis). 



render it unmanageable. As for the insect, it simply obeys its 

 maternal instinct, which commands it to deposit its eggs under the 

 skin of our large ruminants. 



Let us now explain how the eggs of the CEstrus deposited in 

 the skin of the bullock accommodate themselves to this strange 

 abode. The mother insect makes a certain number of little 

 wounds in the skin of the beast, each of which receives an egg, 

 which the heat of the animal serves to bring forth. It is a 

 natural parallel to the artificial way which the ancient Egyptians 

 invented of hatching the eggs of domestic fowls, and which has 

 been imitated badly enough in our day. 



Directly the larva of the Bot-fly is out of the egg and lodged 

 between the skin and the flesh of its host, the bullock, it finds 

 itself in a place perfectly suitable to its existence. In this happy 

 condition the larva increases in growth, and eventually becomes a 

 fly in its turn. Those parts of the animal's body in which the 

 larvae are lodged are easily to be recognised, as above each larva 



