ORGANS FOR BREATHING IN WATER-GRUBS. 155 



usually swim near the surface of the water, with their 

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

 pose which will presently be obvious. These grubs, 

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

 dance during the summer, in ditches or in water- 

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

 parent 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 terminal 

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

 are its tail and its breathing-tube, both of which end in 

 a sort of funnel, composed of hairs in form of a star, 

 anointed with oil, so as to repel water. Swammer- 

 dam remarks that when, by handling it too roughly, 

 this oil is removed, the grub "can no longer suspend 

 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- 



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



