INFUSORIA. 101 



plex structure. Others, like Miiller, Cuvier, and Lamarck, have con- 

 sidered them to be gifted with an organization extremely simple. We 

 shall probably find that the truth lies between these two extremes. 



In the superior Infusoria, besides the granules, the interior globules, 

 vesicles full of liquid, vibratile cils, and a tegumentary system, more 

 or less complex, we find the substance which is called Sarcoda. 



The digestive apparatus of the Infusoria has been the subject of 

 numerous observations, and has been provocative of very animated 

 discussions. In the inferior order of the class, which comprehends 

 the very smallest animalcules, it has not been found possible to observe 

 the organization of the digestive apparatus in a satisfactory manner. 

 Some writers think they have no mouth, what has been taken for that 

 organ being only hollow dimples on the surface of the body ; others 

 recognize the existence of a buccal orifice, sometimes furnished with 

 a solid armature. As to the arrangements of the interior cavities in 

 which digestion takes place, we know nothing certain. 



The digestive apparatus is better understood in the superior Infusoria, 

 called ciliate, namely, those provided with vibratile cils. These cils 

 seem to determine the currents of the liquid, leading the nutritive cor- 

 puscles suspended in the water towards the entrance of the digestive 

 apparatus. They form, in some sort, the prehensile organs which seize 

 the aliment. The cils are, at the same time, the organs intended 

 to facilitate respiration; in short, these little whips playing upon 

 the water unceasingly round the Infusoria, is just the action required 

 for the absorption of the oxygen contained in the water. These 

 cils, then, serve at once for the propulsion of the animal, for its 

 nutrition, and for its respiration, presenting a remarkable example of 

 cumulative functions in physiology. 



The corpuscles of nutritive substances directed towards the buccal 

 orifice by the vibratile cils soon disappear in the interior of the animal. 

 Availing himself of this fact and the transparency of the animal, Herr 

 Gleichen, a German physiologist of the last century, conceived the 

 happy idea of colouring the water which contained these animalcules 

 with a finely-powdered carmine; he traced the colouring matter in 

 the bodies of some of them. But it was reserved for Ehrenberg to avail 

 himself of the same artifice in order to study the internal structure 

 and mode of absorbing nutritive matter in these minute creatures. 

 This physiologist fed many groups of Infusoria, some of them with water 



