2 INTRODUCTION. 



making a free adaptation of the admirable thesis propounded by the illus- 

 trious Oken, we find in their primeval shape the very bricks and mortar 

 out of which the entire superstructure of the organic world has been 

 erected. So early as the year 1805, long before the conception of the 

 unicellular nature of the Infusoria by Theodor von Siebold, this astute 

 philosopher, the co-originator with Goethe of the vertebrate theory of 

 the skull, had enunciated the opinion that the infusorial animalcules 

 consisted of simple cells or vesicles, and formed the protoplasmic basis 

 from whence all higher organisms were fashioned or evolved, and into 

 which condition of simple cells or vesicles these same higher organisms 

 were again resolved by the process of dissolution. The divine fiat, " Dust 

 thou art, and unto dust thou shalt return," thus received unconsciously at 

 the hands of Oken a practical and truly remarkable illustration. Finally, 

 among the world of Infusoria we arrive at that dim boundary line, too 

 subtle and obscure for arbitrary definition, that separates, or more correctly 

 blends into one harmonious whole, the two departments of the animal and 

 vegetable worlds ; and here, moreover, with all reverence be it said, we 

 approach, if anywhere, the confines of the organic and inorganic, and are 

 brought face to face with that already half-lifted veil behind which lies, 

 waiting to reward our patient search, the very clue to the deep mystery of 

 Life itself. 



Postponing to a succeeding chapter a detailed account of the structural, 

 developmental, and other vital phenomena pertaining to the Infusoria, as 

 made manifest by the light of modern investigation, it has been decided 

 that some space in the first instance might be advantageously devoted to a 

 brief epitomization of the more important epochs in the history of these 

 minute organisms, as accumulated step by step from the time of their earliest 

 discovery. As a matter of necessity, man's acquaintanceship with the puny 

 members of this organic group has been comparatively short, and is co-ex- 

 tensive only with the invention and practical application of the microscope. 

 None of the myriad forms — though in some few instances conspicuous in 

 their concrete state or discernible individually by the unassisted vision, as 

 mere moving points — yield up the secret of their separate organization and 

 life-history without the aid of that most invaluable and indispensable 

 auxiliary to biological discovery. In like manner, our present advanced, 

 though still far from perfect knowledge, of the Infusoria has been acquired 

 by slow degrees, and contemporaneously with the improvements made upon 

 that instrument, each successive stage of progress achieved in this direction 

 representing, indeed, but a reflex of the higher perfection of the appliances 

 placed from time to time at the disposal of the histologist through the 

 augmented skill of the optician. It is much to be regretted that authentic 

 evidence is wanting that can identify with absolute certainty the first 

 inventor of the microscope, or rather of those simple spheres of glass 

 or doubly convex lenses, mostly home made, employed over two centuries 

 ago, with which in the hands of the earliest investigators, as presently 



