174 NATURAL HISTORY OF AQUATIC INSECTS CH. 



as long as the body, and tapers very gradually to its 



free tip. Here we find a 

 curious radiate structure, 

 rather like the peristome 

 of a moss-capsule, which 

 seems adapted for open- 

 ing and closing. There 

 is, however, no orifice 

 which the most careful 

 scrutiny has succeeded 

 in discovering. A deli- 

 cate membrane extends 

 between the teeth, and 

 prevents any passage in- 

 wards or outwards of air 

 in mass. The tube en- 

 closes a large trachea, the 

 continuation of one of 

 the main tracheal trunks. 

 This is stiffened by a 

 spiral coil, but at inter- 

 vals we find the coil de- 

 ficient, while the wall of 

 the tube swells out into 

 a thin bladder. How- 

 ever the tube is turned, 

 a number of these 

 bladders come to the 

 surface. As the pupa 

 lies on the surface of 

 the mud, the filament 



floats on the top of the water, and the air 



X '00 



FIG. 58. Pupa of Ptychoptera paludosa, 

 with long respiratory tube. A second 

 (rudimentary) tube is also seen. '1 he 

 figures to the left show the extremity of 

 the tube, and a portion of the middle, 

 both highly magnified. The trachea 

 lies in the tube. Both thin out at the 

 bladder-like swellings, and come close 

 together, as if to allow a free inter- 

 change of gases. 



