10 



Dragon-Flies : their Life-History. [Sess. 



magnified, they are seen to be possessed of two strong claws, 

 sometimes divided into four at the tips, and two rows of 

 formidable-looking spines on the inner or under side of the 

 leg. 



Metamorphosis frequently induces remarkable changes in 

 the system of nutrition of insects, but such is not the case 

 with dragon-flies, further than that in the larval condition 

 the food consists of aquatic insects, whereas in the mature 

 form it consists of winged insects. They eat their prey com- 

 pletely, not contenting themselves by merely sucking its 

 juices. An examination under the microscope of the con- 

 tents of the digestive tube easily verifies this statement, there 

 being found in every case the remains of heads, eyes, legs, 

 wings, and antenna — the indigestible portions being rejected 

 as nearly dry pellets in the course of nature. The change, 

 however, in the respiratory system, produced by metamor- 

 phosis, is sufficiently striking, being now carried on, as in 

 many other insects, through direct contact with the air by 

 means of spiracles, of which there are several pairs — two to 

 each segment — close to each other, on the under side of the 

 abdomen, where the dorsal and ventral surfaces really join. 

 They are oval in form, and are supplied on both sides with a 

 delicate fringe of hairs. 



Many instances have been cited of the migration of dragon- 

 flies. Some species are often seen at sea, far from land, in 

 calm weather, in troops which are no doubt migratory : our 

 common Libellula quadrimaculata, which inhabits the cold 

 and temperate regions of the northern hemisphere, has been 

 frequently seen in immense migratory swarms. At a certain 

 season of the year the northern winds sweep a host of a 

 species into Havannah and its environs. Kirby & Spence, in 

 their introduction to ' Entomology,' note the following instances : 

 " Meinecken states that, on a clear day, he once saw in a 

 village in Anhalt, about 4 in the afternoon, such a cloud of 

 dragon-flies (Libellula clepressa) as almost concealed the sun, 

 and not a little alarmed the villagers, under the idea that they 

 were locusts." Mr Woolnough of Hollesley, in Suffolk, once 

 witnessed such an army of the smaller dragon-flies (Agrion) 

 flying inland from the sea as to cast a slight shadow over a 

 field of four acres as they passed. But the greatest on record 



