200 NATURAL HISTORY OF AQUATIC INSECTS CH. 



extremity of the foremost pair of feet is not cylin- 

 drical as in the rest, but flattened, and the hooks 

 project from it like the fingers from a hand.^ 



The larvae of Eristalis were first brought to Reau- 

 mur singly, and had been found on the ground. He 

 did not then know that the larva is really aquatic. 

 One day however he emptied a bell-glass which con- 

 tained water as well as the remains of many Insects 

 and leaves. The mud at the bottom was black and 

 putrid. In it were seen more than two hundred long- 

 tailed larvae. He washed them in clean water, when 

 they were seen to be of whitish colour. They were 

 divided into parcels, and put into separate vessels, 

 which were filled with water to a depth of two inches. 

 Before long the use of the long tail appeared. At 

 first the larvae moved about in various ways, some 

 swimming through the water, others creeping on the 

 side of the vessel or at the bottom ; but in less than a 

 quarter of an hour all were at rest, their long slender 

 tails just reaching the surface. Some had the hinder 

 end of the body nearly vertical and in line with 

 the tail ; others were creeping on the bottom, the tail 

 being nearly at right angles with the body. Some 

 had the tail straight, while in others it was thrown 

 into a single or double curve. 



Since the water in the vessel was about two inches 

 deep, the tails were of that length also — very long for 

 larvae whose bodies were at most two thirds of an 

 inch in length. To ascertain whether the}' could 

 lengthen them >'et more, Reaumur added water to 



1 The larva can sometimes be seen to creep upon tlie under- 

 side of the surface-film by means of its feet. 



I 



