82 THE VITAL FUNCTIONS. 



of ascertaining the nature of the organization of 

 these cnrious beings ; but as no mode presented 

 itself of dissecting objects of such extreme minute- 

 ness, it was only from the external appearances they 

 presented under the microscope, that any inferences 

 could be drawn with regard to the existence and 

 form of their internal organs. In most of the larger 

 species, the opaque globules, seen in various parts 

 of the interior, were generally supposed to be either 

 the ova, or the future young, lodged within the 

 body of the parent. In the Rotifer, or wheel ani- 

 malcule of Spallanzani,* a large central organ is 

 plainly perceptible, which was by some imagined to 

 be the heart ; but which has been clearly ascertained 

 by Bonnet to be a receptacle for food. Muller, and 

 several other observers, have witnessed the larger 

 animalcules devouring the smaller; and the infer- 

 ence was obvious that, in common with all other 

 animals, they also must possess a stomach. But 

 as no such structure had been rendered visible in 

 the smallest species of infusoria, such as monads, 

 it was too hastily concluded that these species 

 were formed on a different and a simpler model. 

 Lamarck characterized them as beino; 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 on the subject by Professor 

 Ehrenberg, whose researches have recently dis- 



* Vol. i. p. 53, Fig. 1. 



