164 NATURAL HISTORY OF AQUATIC INSECTS CH. 



other. There are few better examples of adaptive 

 resemblance. 



The pupa of Dixa is coiled into a nearly circular 

 disc, the abdomen being bent forwards beneath the 

 thorax. It has a pair of respiratory trumpets behind 

 the head, and either floats in a vertical position at 

 the surface of still water, or lies surrounded by the 

 vegetation which grows on the margin. It moves 

 but little, so far as I have seen. 



The larva is of a full black colour, and very incon- 

 spicuous upon decaying vegetation. It may be found 

 from spring to late autumn, though in the height of 

 summer, when the transformation occurs, the larvae 

 become scarce. Though very few English naturalists 

 have seen them, they are probably common enough. 



DlCRANOTA. 



At the bottom of muddy pools and slow streams 

 there may often be found small red worms, half 

 buried in the mud. They attain a length of perhaps 

 a couple of inches. The head-end is concealed in 

 mud. The tail-end, which is more slender, projects, 

 and waves to and fro in the water, as if to effect the 

 aeration of the blood. If withdrawn from the mud, 

 the worms throw themselves into tight coils, and 

 sometimes form a tangled mass at the top of the mud. 

 The red colour is due to haemoglobin in the blood, 

 which courses along fine vessels, as in the Earthworm, 

 to which this animal, which is called Tubifex, is 

 rather closely related. Tubifex moves or withdraws 

 itself into its burrow by means of hooks projecting 



