INTERNAL ANATOMY OF INSECTS. 59 



emit it a . This brisk motion probably disengages it from 

 the water. In many species, when in repose, they are 

 laid upon the back of the animal b , but in others they are 

 not c . 



The larvae of the Agrionida appear to respire like 

 those of the Ephemera, &c. by means of long foliaceous 

 laminae or false gills filled with air-vessels ; but instead 

 of being ventral, they proceed from the anus. They are 

 three in number, one dorsal and two lateral, perpendi- 

 cular to the horizon, of a lanceolate shape, beautifully 

 veined, with a longitudinal middle nervure, from which 

 others diverge towards the margin, which are probably 

 bronchia. They are used by the animal, which swims 

 like a fish, as fins, but it does not appear to imbibe the 

 water like the other Libellulina, nor to propel itself by 

 ejecting it, a circumstance which furnishes an additional 

 argument for the more received opinion, that this action 

 in them is for the purpose of respiration as much as for 

 motion d . 



The larvae and pupae of the Libellulina, receive the 

 water and air that they respire by a large anal aperture, 

 which is closed at the will of the animal by five hard, 

 moveable, triangular, concavo-convex pieces, all very 

 acute and fringed with hairs. These pieces are placed 

 so that there is one above, which is the largest of all ; 

 one on each side, which are the smallest, and two below; 

 when these are closed they form together a conical point 6 . 

 Sometimes only three of these pieces are conspicuous f : 



a Reaum. vi. 465. b Ibid. t. xlii./. 4, 5. De Geer ii. 623. 



c Ibid. 648. *. xvii./. 11, 12. 



d VOL. III. p. 154. De Geer ii. 697. t. xxi./. 4, 5, 12. 



e De Geer Ibid. 666. t. xix./. 6. 



f Reaum, vi, 393. t. xxxvi./, 8, 9, 1. 1. 



