HOW IXSECTS BREATHE. 147 



usually in the very foulest water, it has nothing to fear 

 from the attacks of more powerful insects, and does not 

 require to conceal itself. It is provided with a tail about as 

 long as the body, and perforated at the end. Two large 

 tracheae pass down the body, uniting posteriorly into one, 

 which, after forming several coils at the base of the tail, passes 

 up that organ, without being attached to it, and finally opens 

 at the end into a large spiracle, surrounded with a star of 

 hairs. The loose coils can, if necessary, be protruded up the 

 tail, so as to extend the tail, if necessary, to five or six 

 inches in length. 



By this curious apparatus the animal is enabled to breathe 

 air while remaining at some inches depth in water. 



In the larvae of Ephemera we met with a very different 

 type. These animals live in ponds and ditches, where, if they 

 were as defenceless, and at the same time as inactive as the 

 larvae of Er tst alts, they would soon fall a prey to some 

 enemy more powerful than themselves ; and though they are 

 so formed as to swim with rapidity, even this would be of 

 little avail if they had to remain at the surface of the water 

 to breathe. They are therefore provided with branchiae, and 

 are thus enabled to remain hidden among the thickets of 

 water-plants. 



The branchiae are attached by pairs to the sides of the ab- 

 dominal segments, making four to each segment. They 

 consist sometimes of two leaves, as in JE. vubjata, or of a 

 leaf and a bunch of hairs, as in E, fuscogrisea, or sometimes 

 of a narrow stalk clothed on each side with hair-like pro- 

 cesses, as in De Geer, vol. ii. pi. 16, f. 3. The leaves agree in 

 structure with the wings of the perfect insect, being formed 

 of a flattened bag into which trachea' send branches. 



Thus as we find many insects with abdominal legs in their 

 larval condition, so we find some which in the same state 



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