44° THE RAT-TAILED WORM FLY, 



were almost all entirely tranquil, and Reamur soon 

 discovered the real use of their long tails. On ex- 

 amining the vessel, he found that each of the ani- 

 mals, in whatever situation they were placed, ex- 

 tended its tail exactly to the surface ; that, like 

 other aquatic insects, the respiration of air was ne- 

 cessary to their existence ; and that the tail, which 

 is tubular, and open at f:he extremity, was the organ 

 by which this operation was performed. In this 

 experiment, the distance from the bottom to the 

 surface was two inches, and, of course, the tails 

 were of an equal lengh. To discover how far 

 the animals could extend their tails, this most in- 

 genious and indefatigable philosopher gradually aug- 

 mented the height of the water, and the tails unL 

 formly rose to the surface till it was between five 

 and six inches high. When the water was raised 

 higher the animals immediately quitted their sta- 

 tion at the bottom, and either mounted higher in 

 the water, or fixed themselves upon the sides of the 

 vessel, in situations which rendered it convenient 

 for them to reach the surface with the points of 

 their tails. — These tails consist of two tubes, both 

 of which are capable of extension and contraction. 

 The first tube is always visible; but the second, 

 which is the proper organ of respiration, is exerted 

 only when the water is raised beyond a certain 

 height. Through this tube the air is conveyed 

 into two large trachea: or wind-pipes within the 

 body of the animal, and thus maintains the prin- 

 ciple of life. When the tails are below the sur- 

 face, the animals occasionally emit small bubbles o( 



