TRACHEA!, (ilLLS. 



535 



only applied externally to the viscera, but partially traverse them 

 and serve at the same time to support them. 



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

 appendages on the body of the larvie of Phryganidce, Ephemeridce 

 (tig. 444), and in the rectum of the larva- of ^Kschnti and Libellula. 



FIG. 441. a, Larva of Ephemera vrith seven pairs of ti-acheal Kills Kt, slightly 



Tk, An isolated tracheal gill, strongly magnified. I, Tracheal system of an Agrimi Inrva 

 (after L. Dufour) ; Tst, tracheal trunk ; Nn, accessory ej T es. 



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. 



