RAT-TAILED LARV^. 375 



terminal tube is a pair of spiracles,, surrounded by 

 five radiating hairs which prevent the access of the 

 water, and thus enable the creature to breathe freely 

 whilst its body is immersed probably to a depth of 

 several inches. These rat-tailed larvse^ as they are 

 called, are also furnished with about seven pairs of 

 tubercular feet, and when full-grown, they quit the 

 water and undergo their metamorphosis in the earth. 

 The larva-skin then hardens to form the case of the 

 pupa, but respiration is no longer performed through 

 the elongated tail, instead of which the air finds a 

 passage through four small horn-like organs which 

 make their appearance in the neighbourhood of the 

 head. One of the commonest of the Flies which 

 proceed from these rat-tailed larvse is the Eristalis 

 tenax, the large brownish-black, bee-like Fly, with its 

 scutellum and two spots at the base of its abdomen 

 diill orange, which we see so commonly hovering, in 

 company vdth the more delicate little Syrphi and 

 some smaller species of its own genus, over the plants 

 in our gardens in the summer months. 



Besides these, this tribe includes a curious group 

 of flies, which, although they are quite destitute of 

 any weapons with which to inflict wounds and suck 

 blood, are yet objects of the greatest terror to our 

 domestic animals. These are the (Estrida, or Bot- 

 flies, in which the proboscis is very rarely present, 

 whilst in the few species which possess such an organ, 

 it is of very small size. Nevertheless they are as 

 persevering in their attacks upon cattle as the Tabani 

 or Breeze-flies, to which I have already referred; and 

 so well do the animals threatened know that their 

 persecutor has anything but their welfare in view, 

 that they exert every stratagem to prevent the insect 



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