146 HOW INSECTS BREATHE. 



vided with branchiae, while those that are powerful and 

 active are without any. Thus the strong predacious larvae 

 ofDyticus and Mydrophilus respire air by means of openings 

 situated at the tail. They hang suspended from the surface 

 of the water, and the attitude which is necessary for respi- 

 ration is also exactly that which gives them the best view 

 of their prey swimming about in the water below. The 

 larvae of some gnats (Culex), though not so large, usually 

 live in places — such as water-butts, cow-troughs, shallow 

 pools, &c, — where they are " monarchs of all they survey ;" 

 and having little therefore to fear from the attacks of larger 

 animals, are provided with a short tube projecting at an 

 angle from the tail, and terminating in a spiracle at the end, 

 and, several hairs by which the insect hangs suspended 

 from the top of the water, and makes from thence short 

 excursions in search of food. 



The larvae of the Trpulidce are found in the most varied 

 situations ; many of them live in water, and one of them is 

 very peculiar. It is quite transparent, and, therefore, rather 

 difficult to find, though not uncommon in clear grassy pools. 

 It floats horizontally and almost motionless, though, when 

 alarmed, it can swim away with rapidity. The breathing 

 organs are four silvery kidney-shaped organs, two placed 

 anteriorly and two posteriorly. This larva is figured by 

 Reaumur, Histoire des Insectes, vol. v. pi. 6, f. 7, 9. I 

 have often met with it in ponds on commons. The pupa is 

 very different, being provided with two pear-shaped branchiae 

 which project like ears from the thorax, and give it a rery 

 peculiar appearance. It floats perpendicularly and has two 

 leaf-like fins at the tail. 



Perhaps, however, the most remarkable Dipterous larva 

 is that of Eristalis tenax, Meig. It is a thick, fleshy, 

 unarmed, sluggish grub, and yet breathes air. Living 



