INTRODUCTION. 35 



the swift, equal to, at least, two hundred and fifty miles 

 in an hour or to be in England at six in the morning, 

 and in Africa before noon, to some of the crawling 

 reptiles that cannot pass over half the number of inches 

 in double the space. Then we find them calculated 

 to move through many kinds of media, through the 

 air, through the water, under the earth, into the sub- 

 stance of timber, and even of stone. Nor does the 

 apparent size or strength appear to signify much ; for 

 with the exception of the points of the piercers that 

 enable them to mine their way, the bodies of the 

 animals that work into the hardest substances are 

 generally soft as well as small. Their passages too are 

 made over all sorts of surfaces, whatever may be their 

 texture or position. The water-flea, (gyrinus natator,) 

 whirls his fairy circles on the pool, with the same ease 

 and the same rapidity as if he were moved by the wind 

 in free space : and when a number of them are gam- 

 bolling upon a glassy pool, they seem, as the exquisite 

 gloss of their black wing-cases glitters in the sun, as 

 if they were sparks of fire rather than living creatures 

 that can move only in consequence of muscular action. 

 The gentle ripple that follows their course, as they 

 wheel and play together, seems to be occasioned rather 

 by their agitating the air than by any action of theirs 

 upon the water, and the glitter of the wing-cases is so 

 constant that in those gyrations, from which they get 

 their specific name, their wings can hardly be used; 

 and yet, small as they are, they must have the means 

 of covering their feet and bodies with an oily coat, to 

 repel the water, in the same manner as ducks and 

 other water fowl preserve their feathers from the same 

 element. 



