TRACHEAL GILLS. 



535 



only applied externally to the viscera, but partially traverse them 

 and serve at the same time to support them. 



Tracheal gills are present in the form of leaf-like or filiform 

 appendages on the body of the larvae of PhryganidcBj EphemeriGix 

 (fig. 444), and in the rectum of the larvae of JSschna and Libellula. 



FIG. 4U. a, Larva of Hp^em^ra with seven pairs of tracheal gills ~Kt, slightly magnified. 

 Tk, An isolated tracheal gill, strongly magnified, b, Tracheal system of an Agrion larva 

 (after L. Dufour) ; Tut, trachoal trunk ; Na, accessory eyes. 



In the last case the walls of the rectum are very muscular, and 

 are capable of regularly pumping in and out water, thus giving rise 

 to a kind of respiratory movement. 



