THE EPHEMERIDJE. 53 



feeding upon vegetable matter. It is stated by 

 some writers that the former feed upon the clay, 

 in which their holes are made. Swammerdam, 

 the celebrated Dutch naturalist, found that sub- 

 stance in their stomach and intestines. " It is 

 therefore most probable," says Mr. Westwood, 

 " that when the larva has assimilated the decaying 

 vegetable matter contained in the mud, the earthy 

 particles are discharged. The larva is provided 

 with six legs, and what are regarded by some 

 writers as a row of fins on each side of the body. 

 These fin-like appendages, however, are, with 

 greater probability, considered by other writers to 

 be the organs of breathing answering to the 

 lungs of land animals, and to the gills of fishes. 

 They are constantly in motion, and are pervaded 

 by little tubes, very curiously arranged, through 

 which the air is supposed to pass. The general 

 form of the larvse resembles that of the perfect 

 insect, with the exception, of course, of wings, and 

 the likeness becomes more and more apparent 

 after each moulting. Its last change, in the water, 

 is into the pupa state, and when this has taken 

 place and the atmosphere is of the proper tem- 

 perature, the insect rises to the surface, and, 

 emerging from its confinement in the pupa skin, 

 appears in the form of a delicate fly. But its 

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