79 INFUSORIA. PART nr. 



or used to push it forward. When the bristles or cilia 

 of this high group of Infusoria are used for crawling 

 their motions may be traced to the contraction of the 

 skin; but in the Infusoria that are never fatigued 

 though their cilia vibrate incessantly night and day, it 

 may be presumed that these motions are altogether 

 independent of the will of the animal, in as much as 

 there are innumerable cilia in the human frame that 

 are never at rest during the whole course of our exis- 

 tence, nor do their vibrations cease till a considerable 

 time after death a striking instance of unconscious 

 and involuntary motion. 



The cell which constitutes the body of the Infusoria 

 is filled with sarcode, which is the receptacle of the food, 

 and in that substance all the internal organs of the 

 animalcule are imbedded. In the higher genera it is 

 full of granular particles of different sizes and forms, 

 and it contains a nucleus in its centre, characteristic of 

 cellular protozoa generally. The nucleus is of a dull 

 yellow colour, and is enclosed in a transparent capsule, 

 which in the smaller Infusoria reflects light brilliantly. 

 It is generally of an ovoid form and single, but in 

 several species the nucleus is double, and in others 

 there are several nuclei. 



The Infusoria have a distinct mouth and gullet, and 

 for the most part another aperture for ejecting the in- 

 digestible part of their food, though some discharge it by 

 the mouth, others through any part of their surface. 

 A few of the larger Infusoria devour the smaller ; others 

 feed on minute vegetable particles, chiefly diatoms. 

 Solid substances that are swallowed are collected into 

 little masses mixed with water, and enter into clear 

 spherical spaces called vacuoles in various parts of the 

 sarcode, where they are partially digested. When the 

 animal has not had food for some time, clear spaces 

 only filled with a very transparent fluid are seen, vari- 



