70 THE VITAL FUNCTIONS. 



are totally unprovided with either pedicle, arms, or tenta- 

 cula; others, furnished with these latter appendages, are 

 equally destitute of such a cavity; and those helonging to a 

 third family possea* a kind of pouch, or false stomach, at 

 the upper part of the pedicle, apparently formed by the 

 mere folding in of the integument. This is the case with 

 the Gcronia, depicted in Fig. 250, whose structure, in this 

 respect, approaches that of the Hydra, already dcscri])cd, 

 where the stomach consists of an open sac apparently formed 

 by the integuments alone. Thence may a regular progres- 

 sion be followed, through various species, in which the aper- 

 ture of this pouch is more and more completely closed, and 

 where the tube which enters it branches out into ramifica- 

 tions more or less numerous, as we have seen in the Rhizos- 

 toma.* It is difficult to conceive in what mode nutrition 

 is performed in the agastric tribes, or those destitute of any 

 visible stomach; unless we suppose that their nourishment is 

 imbibed by direct absorption from the surface. 



Ever since the discovery of the animalcula of infusions, 

 naturalists have been extremely desirous of ascertaining the 

 nature of the organization of these curious beings: but as no 

 mode presented itself of dissecting objects of such extreme 

 minuteness, it was only from the external appearances they 

 present under the microscope that any inferences could be 

 drawn with regard to the existence and form of their inter- 

 nal organs. In most of the larger species, the opaque glo- 

 bules, 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,t 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. JNlullcr, and several other observers, 

 have witnessed the larger animalcules devouring the smaller; 

 and the inference was obvious, that, in common with all 



* See Peron, Annates du Museum, xiv. 330. 

 fVol. i. p.58, Fit,^ 1. 



