INTRODUCTION. Vll 



the geologist nevertheless loves to search out the 

 first or oldest traces of life upon our globe; and 

 so the microscopist delights to view the simplest 

 exhibitions of structures and faculties, which reach 

 their completion in the frame and mind of man. 

 That one great plan runs through the whole uni- 

 verse is now an universally accepted truth, and 

 when applied to physiology and natural history, 

 it leads to most important results. 



The researches of recent philosophers have shewn 

 us that nature cannot be understood by studying 

 the parts of animals with reference merely to their 

 utility in the economy of the creature to which 

 they belong. We do, indeed, Und an admirable 

 correspondence between structures and the services 

 they perform; but every object in creation, and 

 every part of it, is in harmonious relation to 

 some grand design, and exhibits a conformity to 

 some general mode of operation, or some general 

 disposition and direction of forces, which secures 

 the existence of the individual or the species, and 

 at the same time works out the most majestic 

 schemes. Microscopic researches, such as are witliin 

 the reach of millions, offer many of the most 

 beautiful illustrations of these truths; and although 

 the following pages are confined to such objects 

 as are easily obtainable from ponds, and relate 

 almost exclusively to the Infusoria, the Rotifers, 



