.T. 



THE ANIMALS OF THE FRESHWATER AQUARIUM 115 



of furnishing food approaches, however, it is suddenly shot out, 

 and proves to bear two prehensile " jaws " at its tip, by means of 

 which the animal is seized and brought within reach of the mouth. 

 The process, which is very interesting, should be carefully watched 

 in a captive form. The larva is naturally sluggish, moving about 

 but little, and spending most of its time lying in wait for its prey 

 in the mud at the bottom of 

 the pond. Very curious also 

 are its respiratory organs. 

 The posterior part of the ali- 

 mentary canal is furnished 

 with abundant air-tubes, and 

 in order that these may be 

 constantly supplied with fresh 

 oxygen, water is made to flow 

 in and out of this region by 

 gentle pulsations of the ab- 

 domen. If, however, the larva 

 be startled it suddenly ejects 

 this water of respiration, and 

 as a result it darts suddenly 

 forward, often with great 

 swiftness. A very peculiar 

 feature of the larva, as com- 

 pared with the caddis, is 

 that rudimentary wings are 

 present from the first. In the 

 other type of larva, respiration 

 is carried on in a somewhat 

 different fashion. In this case the end of the body is furnished 

 with three transparent leaf-like plates, whose primary function 

 is to enable the larvae to swim, but which seem also to have a 

 respiratory function. These forms are much more" active than 

 their allies, for not only do they swim through the water by means 

 of these delicate appendages, but they also climb actively about 

 by means of their long legs. The larva of Calopteryx virgo, the 

 demoiselle dragon-fly, is a good example (see Fig. 52). 



As already mentioned, no striking change in form occurs 



FIG. 52. Mature nymph of the demoiselle 

 dragon-fly (Calopteryx virgo}. 



