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INTRODUCTION TO ZOOLOGY 



of each wing sloping away at a very marked angle from the 

 mid-line where the two meet (Fig. 235). They fly heavily, 

 and will often begin to run away before they take to flight. 



Fig. 235. 





-The Alder-fly {Siaiis lutaria). 

 (x2.) 



Fig. 236.— Eggs of Alder-fly. 



A, Natural size and position ; B, a few 

 enlarged and seen from the side. 



The body is thicker relatively to its length, and the antennae, 



though long, are shorter than in the Caddis-fly, for which it 



is sometimes mistaken ; also its wings are free from the 



small hairs which are characteristic of Caddises. 



„, _ The eggs are laid, not 



The Eggs. ... f r, i 1 ., 



m the water, but on a plant, 



a stone, or a piece of wood, sometimes 



some yards away from the stream or 



river in which the larvae will live. 



The eggs are cylindrical, and are to 



be found in early May deposited in 



clusters of some hundreds together, 



neatly arranged in a series with their 



outer pointed ends free. 



When the larvae hatch, 



they have to wriggle their 



way down to the water, and many of 



them are said to lose their way and 



never reach their goal. The larval 



aquatic life is spent chiefly on the mud 



at the bottom of the water, and it lasts 



about a year. The head of the larva 



bears two short antennae and has 



well-developed mandibles, with which it 



attacks the other aquatic larvae on which 



it feeds. The thorax is large and very 



clearly divided into three segments 



which bear three pairs of legs ; the abdomen has the usual ten 



The Larvae. 



Fig. 237-— The Larva of 



the Alder-fly. 



g, One tracheal gill. 



