198 



SYSTEMATIC ZOOLOGY 



Fig. 194. Ephemera, a May 



fly and larva. (Aftei Guerin 

 and Percheron, from Parker 

 and Haswell's Text-book.) 



divided into seven orders ; thus the group as it stands here 

 includes insects which differ considerably in structure, such as 

 the May flies, dragon flies, stone flies, and certain kinds of lice. 



These animals, with the exception of the 

 wingless lice, have two pairs of thin, mem- 

 branous wings, usually richly veined. In 

 the May flies, the mouth parts are rudi- 

 mentary, but in the others they are adapted 

 for biting. A very important characteristic 

 of this order is found in the development, 

 in which there is an incomplete metamor- 

 phosis. 



The May flies (Figs. 194 and 194 bis) 

 are very delicate insects, living near the 

 water and at- 

 tracted in the 

 evening by 

 bright lights. 

 The wings are 

 thin and trans- 

 parent, the 

 anterior pair 

 relatively large, the posterior small or 

 absent. To the posterior end of the 

 abdomen two or three long filaments 

 are attached. The adult insect, or 

 imago, generally lives only a few 

 hours, but the aquatic larvae, or 

 nymphs, may live from one to three 

 years, and are generally provided with 

 tracheal gills. 



The dragon flies (Fig. 195), some- 

 times called darning needles, or mos- 

 quito hawks, have the two pairs of 

 wings of nearly equal size. The larvae 

 are aquatic, and are readily distinguished from other aquatic 

 larvae by the mouth parts, particularly the second maxillae 

 fused into a lower lip ; this is very large and as it covers 

 the other mouth parts is called the mask ; its powerful jaws 



FlG. 194 bis. Ephemera 



a May fly. Af, ana! filaments. 



(From Claus and Sedgwick's 



Text-book.) 



