92 THE VITAL FUNCTIONS. 



is performed in the agastric tribes, or those 

 destitute of any visible stomach ; unless we sup- 

 pose that their nourishment is imbibed by direct 

 absorption from tlie surface. 



Ever since the discovery of the animalcula of 

 infusions, naturalists have been extremely de- 

 sirous of ascertaining the nature of the organi- 

 zation of these curious beings : but as no mode 

 presented itself of dissecting objects of such 

 extreme minuteness, it was only from the ex- 

 ternal appearances they present 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 

 animalcule 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 inference was obvious that, 

 in common with all other animals, they also 

 must possess a stomach. But as no such struc- 

 ture had been rendered visible in the smallest 

 species of infusoria, such as monads, it was 



* V\)l. i. ]). fi'2, Fis:. 1 . 



