4 Dragon-Flics : their Life-History. [Sess. 



flies, testifying not only to their voracity but to their sluggish 

 habits as well, is the curious modification of the labium or 

 lower lip, long ago termed a " mask," — a term, however, which 

 does not indicate its full character. Of this almost unique 

 organ I have made preparations from three different species. 

 It is seen to conceal the mouth entirely, is sometimes flat, 

 sometimes arched, and serves the function of an arm and hand, 

 furnished in the largest species with two very strong claws or 

 pincers, and within them two movable parts supplied with a 

 row of teeth. Imagine your arm attached to your chin or 

 neck, and you have an idea of this powerful prehensile organ. 

 It has two joints : the first forms the attachment under the 

 head, and, along with the second, thrusts the apparatus out- 

 wards with astonishing rapidity for seizing prey, or withdraws 

 it to its resting position. The second joint, when the appa- 

 ratus is folded up, reaches backward to the second pair of 

 legs, and when thus folded the strong claws are, with the 

 prey they may have seized, brought into close contact with 

 the mouth. In the Agrionidae the mask is triangular in out- 

 ward appearance, and the claws show a development approach- 

 ing the large claws of the crab. There is also a fringe formed 

 by a few strong hairs. In the type shown, midway between 

 these two, that of the Libellulidse, the mask is arched, and the 

 prehensile portion is divided into three nearly equal parts, the 

 outer two of which are movable. With their closely applied, 

 serrated edges, they remind one of the sides of a patent exca- 

 vator, which take up everything found inside, after they are 

 drawn together. 



Eespiration in dragon-flies is performed by the valvular 

 apparatus, formed by three membranous plates, in connection 

 with the duct or canal at the extremity of the abdomen. This 

 apparatus — guarded from accident by the spinous processes 

 mentioned, and in Libellula by strong hairs set at right angles 

 to them in addition — causes alternately a strong inrush and an 

 expulsion of water. The water, on being drawn in, comes in 

 contact with the thin walls of the tracheae, its oxygen is ex- 

 hausted, and it is then expelled to admit a fresh supply. The 

 currents resulting from these operations are easily seen, if the 

 water in which the larvae are placed is turbid or slightly 

 muddy, as the particles are then observed to be drawn to and 



