58 INTERNAL ANATOMY OF INSECTS. 



differ in form. In the larva and pupa of Ephemera vul- 

 gata there are six of these double false gills on each side 

 of the abdomen, the three last segments being without 

 them ; each branch consists of a long fusiform piece, ra- 

 ther tumid and terminating in a point, which is fringed 

 on each side with a number of flattish filaments, blunt 

 at the end. An air- vessel from the trachea enters the 

 gill at its base ; is first divided into two larger branches, 

 each of which enters a branch of the false gill. These 

 branches send forth on each side numerous lesser rami- 

 fications, one of which enters each of the filaments a . In 

 another species (E. vespertina) each false gill presents 

 the appearance of a pair of ovate leaves with a long 

 acumen, and the air-vessels represent the midrib of the 

 leaf, with veins branching from it on each side b ; and, to 

 name no more, in E.fusco-grisea, one branch represents 

 the leaf of a Begonia, the sides not being symmetrical, 

 with its veins, while the other consists only of numerous 

 branching filaments c . In other aquatic larvae, as in that 

 of the common May-fly (Sialis lutaria\ these appendages 

 consist of several joints d . 



By the above apparatus these aquatic animals are en- 

 abled to separate the air from the water, as the fish by 

 their gills ; but how this separation is made has not been 

 precisely explained. The false gills in many species are 

 kept in continual and intense agitation. When they 

 move briskly to one side, Reaumur conjectures they may 

 receive the air, and when they return back they may 



3 PLATE XXIX. FIG. 5. De Geer ii. 624. 

 b Ibid. FIG. 4. De Geer Ibid. 647. 

 c Ibid. FIG. 3. De Geer Ibid. 653. 

 d Ibid. FIG. 6. De Geer Ibid. 727. 



