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INTRODUCTION TO ZOOLOGY 



CHAP. 



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 (Sialis lutarid). 

 (x2.) 



FIG. 236. -Eggs of Alder-fly. 



A, Natural size and position ; 7J, a few 

 enlarged and seen from the side. 



The Eggs. 



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 

 in 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. 



