ii AQUATIC BEETLES 39 



bladder are cut, no more gas is formed. Oxygen 

 could not be made to diffuse into the air-bladder of a 

 Pike, which was filled with atmospheric air and sur- 

 rounded by pure oxygen, but when the epithelium 

 was killed by maceration in distilled water, oxygen 

 readily passed through by diffusion. Bohr accord- 

 ingly adopts Moreau's view, viz. that oxygen is not 

 passed into the air-bladder by diffusion, but is formed 

 within it by " specific secretion." 



The Gyrinus larva feeds upon water-insects, and 

 possibly upon other aquatic animals. Failing these, 

 it will eat the tender parts of submerged plants. It 

 has been noticed that well-fed larvae produce larger 

 Beetles than those which have had a poor supply. 



The pupa of Gyrinus is so well hidden that few 

 naturalists have ever seen it. Modeer, quoted by 

 De Geer (Tom. IV. p. 364), says that about the 

 beginning of August the larva creeps out of the 

 water by climbing up the water-plants, and then spins 

 a grayish cocoon pointed at both ends. Enclosed in 

 this cocoon it changes to a pupa, and emerges as a 

 perfect Insect towards the end of the same month. 

 Modeer adds that the pupa is very liable to the 

 attacks of Ichneumons. 



Dytiscus.i 



No one can hunt long for water-insects without 

 coming across the rapacious Dytiscus. There are 



' Dytiscus is the name originally given to this insect by 

 LinniEus, and used in most systematic books, but Dyticiis., 

 which has the same meaning (fond of diving), has also been 

 applied to it by some authors. 



