HOW INSECTS BREATHE. 149 



with branchiae in the form of hairs, situated on the thorax 

 and anterior portion of the abdomen, which is most exposed 

 to the action of water. 



The only other aquatic larvae which I propose to mention 

 are those of the Libellulidce or dragon-flies : they are slow, 

 awkward insects living in ditches and shallow ponds, and, 

 like the preceding, are provided with branchiae. But why? 

 Covered with a tough leathery skin, large and armed with 

 powerful jaws, they are well able to protect themselves, and 

 are, in fact, entirely carnivorous. The reason, however, 

 is evident. Unable to overtake their prey by the chase, they 

 lie in wait, hidden by the mud at the bottom of the water, 

 and seize any unwary little creature that may pass within 

 reach. It is evident that they would stand a good chance 

 of dying of starvation if they were compelled to leave their 

 hiding-places, and remain at the surface of the water for 

 air. Moreover, if their branchiae were situated on the 

 anterior part of the body, like those of Parapoynx, or on the 

 abdomen, as in Ephemera, a large surface would necessarily 

 be uncovered, which would serve as a warning to the little 

 creatures which constitute their prey. They are therefore 

 situated at the tail, and in the genus Agrion are in the 

 form of elongated leaflets in which the tracheae ramify as 

 usual. 



In the larvae of JEschna and Libellula (dragon-flies),* on 

 the contrary, the respiratory organs are formed on a type which 

 is without a parallel, and which, though so familiar with the 

 fact, I can never contemplate without a feeling of awe and 

 admiration. The water is sucked in through the posterior 

 orifice into the rectum or lower part of the intestinal canal, 

 on the walls of which the tracheae ramify in great numbers, 



* Burmeister's Man. p. 169 ; Leon Dufour, Ann. de Sci. Nat. 1S52, 

 p. 91. 



