46 OUTLINES OF NATURAL HISTORY. 



before it assumes its final characters. The eggs are laid 

 in the water, and the young insect, when hatched, presents 

 the appearances seen in fig. 17, B. It exhibits a head, 

 thorax, with three pairs of legs, and abdomen ; but it 

 shows no traces of wings. It swims about actively in the 

 water, and devours smaller insects by means of its powerf id 

 jaws. It breathes by means of a tuft of valvular appen- 

 dages placed at the end of the abdomen, which can be 

 opened so as to allow the water to gain access to the 

 intestine, the sides of which are furnished with folds con- 

 taining within them breathing-tubes. When the blood 

 has been thus purified, the water is thrown out from the 

 intestine, and the jet thus produced drives the animal in 

 the opposite direction. After a while the insect passes 

 into a second stage (fig. 17, C), in which it resembles the 

 preceding in most respects, but has rudimentary Avings (iv) 

 placed upon the back of the thorax. It is still active and 

 voracious. Again after a while, the aninral drags itself 

 out of the water, and climbs upon some plant. Its skin 

 then dries, and splits along the back, and the perfect 

 insect, with its fully developed wings (fig. 17, A) is set 

 free, and flies away to lead an active existence in the air. 

 These remarkable changes constitute what is known as the 

 "metamorphosis" of the insect (Greek, me^a, indicating 

 change, and morphe, shape). 



jEsluia grandis is the largest of British Dragon-flies, at- 

 taining a length of about two and a haK inches. Its gen- 

 eral colour is yeUowish-brown, with two yellow lines on 

 each side of the thorax, and the abdomen variegated with 

 green or yellow spots. At all periods of its life, and 

 especially in its winged state, it is a most active and 

 voracious insect, living upon other insects ; in its final 

 stage, in spite of its ferocity and destructiveness, it is one 

 of the most beautiful and graceful of insects, from its 

 large and brilliant eyes, its lustrous wings, and the ease 

 and power with which it performs the most rapid evolu- 

 tions in the air. 



Kecapitulation of Essential Characters. — The 

 body is composed of a succession of rings, and is divis- 



