368 THE ATHERICERA. 



the Fly breaks out of its prison is exceedingly curious. 

 Dr. Reissig states that, when ready to escape, the Flies 

 of the genus Tachina, upon which his observations 

 were made, convert their heads into a sort of hydraulic 

 press, by pumping all their fluid into its interior, 

 until it is swelled up into a globe of considerably 

 greater breadth than the rest of the body, the pressure 

 thus obtained being sufficient to split off a sort of 

 cap at the end of the dried larva-skin, forming an 

 aperture through which the insect can emerge. When 

 the expansion has reached its maximum, the head 

 forms a perfect globe, from the surface of which only 

 the last joints of the antennae and the proboscis with 

 its palpi project ; and it is interesting to find that the 

 palpi, which in the perfect fly would seem to be of little 

 or no use, are very serviceable in this operation, for 

 their extremities, being pressed into the side of the 

 larva-skin, at the precise point where the circular cleft 

 of the cap is to be produced, assist greatly in its form- 

 ation. Dr. Reissig also states that, by the same pro- 

 cess, flies which have emerged from their pupae in the 

 interior of hard substances, are enabled to make their 

 way into the free air, and adds, that he observed a 

 specimen of a Tachina, which he had enclosed in a 

 narrow glass tube, attempt more than a hundred times 

 to expel the cork by the expansion of its head. 



Having commenced this section with one of its 

 species which is generally regarded as a plague, it 

 may perhaps be as well to continue a little while in 

 the same strain, for there are several other species 

 belonging to this tribe whose habits are still more 

 disagreeable to us than those of the common House- 

 fly. In fact this little insect, although sufficiently 

 troublesome, does very little actual damage either to 



