DIPTERA. 63 



the CEstriis terrifies a bullock to such an extent as to render it un- 

 manageable. 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 arti- 

 ficial 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 be- 

 tween 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 mcreases in growth, and eventually becomes a fly in its 

 turn. Those parts of the animal's body in which the larvse are lodged 

 are easily to be recognised, as above each larva may be seen an eleva- 

 tion, a sort of tumour, termed a bot— a bump, as Reaumur calls it, 

 comparing it more or less justly to the bump caused on a man's head 

 by a severe blow. 



Fig. 46, taken from a drawing in Reaumur's Memoirs, represents 

 the bots of which we speak. 



The country people are well aware of the nature and cause of 

 these bots. They know that each one contains a worm, that this 

 worm comes from a fly, and that later it will be transformed into a 

 fly itself Each of these bots has in its interior a cavity, occupied by 

 a larva, which, as well as the bot, increases in size as the larva be- 

 comes developed. 



It is generally on young cows or young bullocks— in fact, on 

 cattle of from two to three years of age— that these tumours exist, 

 and they are rarely to be seen on old animals. The fly, which by 

 piercing the skin occasions these tumours, always chooses those 

 whose skin offers little resistance. Each tumour is provided with a 

 small opening, by which the larva breathes. 



In order to examine the interior of the cavity, Reaumur opened 

 some of these tumours, either with a razor or a pair of scissors. He 

 found them in a most disgusting state. The larva is lodged in a regu- 

 lar festering wound, matter occupying the bottom of the cavity, and 

 the head of the worm is continuallv, or almost continually, plunged 

 m this hqmd. " It is most likely very well off there," says Reaumur ; 

 and he adds that this matter appears to be the sole food of the larva. 



