ORGANS FOR BREATHING IN WATER-GRUBS. 155 



ry, they usually swim near the surface of the water, with 

 their heads downwards and their tails in the air, for a 

 purpose which will presently be obvious. These grubs, 

 called scurrs in the north, may be met with in abun- 

 dance during the summer in ditches or in water- 

 butts,* appearing like minute, whitish semi-transpa- 

 rent shrimps or fishes, when their^bodies are a little 

 bent, as they frequently are. 



Aquatic grubs of gnats in a glass vessel of water. 



The organs for breathing, which are very remark- 

 able in the grub of the gnat, are not situated along 

 the sides, as in caterpillars, but in the tail. A tube 

 for the purpose of respiration goes off from the termi- 

 nal ring of the body at an angle. Its main buoys, 

 also, are itsjail and its breathing-tube, both of which 

 end in a sort of ilmnel, composed of hairs, in tbrm of 

 a star, anointed with oil, so as to repel water. Swam- 

 merdam remarks that when, by handling it too rough- 

 \y, this oil is removed, the grub,' can no longer sus- 

 pend itself on the surface of the water; I have, on these 

 occasions, observed it put its tail in its mouth, and 

 afterwards draw it back, as a water-fowl will draw 

 its feathers through its bill to prepare them for resist- 



* iSee Insect Architecture, p. 20, bottom figure, on the right* 



