NUTRITION IN THE INFUSORIA. 93 



too hastily concluded that these species were 

 formed upon a different and a simpler model. 

 Lamark characterized them as being throughout 

 of a homogeneous substance, destitute of mouth 

 and digestive cavity, and nourished simply by 

 means of the absorption of particles through the 

 external surface of their bodies. 



The nature and functions of these singular 

 beings long remained involved in an obscurity 

 which appeared to be impenetrable ; but at 

 length a new light has been thrown upon the 

 subject by Professor Ehrenberg, whose re- 

 searches have recently disclosed fresh scenes of 

 interest and of wonder in microscopic worlds, 

 peopled with hosts of animated beings, almost 

 infinite in number as in minuteness.* In en- 

 deavouring to render the digestive organs of the 

 infusoria more conspicuous, he hit upon the for- 

 tunate expedient of supplying them with coloured 

 food, which might communicate its tinge to the 

 cavities into which it passed, and exhibit their 



* The results of Ehrenberg's labours were first communicated 

 to the BerHn Academy ; they have since been published in two 

 ■works in German : the first of which appeared at Berlin in 

 1830, under the title of " Organisation, Systejnatik und Geo- 

 graphisches Verhultniss der Infusionsthierchen." The second 

 work appeared in 1832, and is entitled " Zur Erkenntniss der 

 Organisation in der Richtung des kleinsten Raumes." Both are 

 in folio, with plates. An able analysis of the contents of the 

 former of these works, by Dr. Gairdner, is given in The Edin- 

 burgh New Philosophical Journal for 1831, p. 201, of which I 

 have availed myself largely in the account which follows. 



