252 PEBSH-WATEK AQtTAEIA. 



they progress with a series of jerks or plunges. Frequently, 

 when a larva or pupa is suddenly reraoved from its aquarium, 

 it will be seen to discharge a tiny stream of water into the 

 air. The water under siich circumstances is sometimes shot 

 no little distance. I was examining lately some of these insects 

 which I had placed in a little water in an ordinary plate, and 

 while lifting gently, with a pair of forceps, the tail part of 

 one of the larvae, some water was driven upon the globe of 

 the lamp by the light of which I was working ; and I do not 

 think I shall be exaggerating when I say that, had not the 

 water been stopped in this way, it would have been thrown 

 nearly 3ft. The insect was not much more than lin. long. 

 Sometimes, when a larva or pupa is returned to its aquarium, 

 it wiU shoot water into the air. In this case the creature seems 

 so anxious to get quickly away from its captor, that it discharges 

 its stream before it is fairly under the surface of the water. 

 If one of these insects is placed upon its back in a little water 

 contained in a plate, the expansion and contraction of its 

 abdomen can be plainly seen as it takes in and discharges 

 the water necessary for respiration. These animals are able 

 to swim upon their backs. 



The lai-vse and pupse of the Agrionides have three rather 

 large leaf-like appendages at the end of their abdomens. 

 These appendages, which are furnished with tracheal tubes 

 connected with others contained within the bodies of the 

 insects, extract the oxygen from the water and supply it to 

 the internal tracheae. The animals often use these gill-like 

 plates in the same way that fish do their tails, and thus they 

 swim somewhat slowly thi-ough the water. 



As the larvae and pupse of Dragon-flies grow, it is neces- 

 sary for them, from time to time, to change their skins. 

 This change of skin is rather frequent, and very complete; 

 so complete, indeed, that sometimes the aquarium-keeper will 

 think that there are two larvae in the same vessel where the 

 night before there was only one. After a certain number of 

 changes of skin, the wing-cases begin to appear, and then 

 the creature has passed from the larval state into that of 

 the pupal. As the time draws near for the nymph to become 



