18 VIEWS OF THE MICROSCOPIC WORLD. 



flow towards these organs, furnish a continual supply of fresh air. According to 

 Mantell, " recent discoveries have shown that cilia exist also in the internal organs 

 of man and other vertebrated animals, and are agents by which many of the most 

 important functions of the animal economy are performed." 



When an animalcule is examined, this delicate member easily eludes observation, 

 but if the creature is placed in a drop of water colored with indigo or carmine, the 

 little whirls and currents created by the action of the cilia are readily detected 

 under the microscope; and upon the evaporation of the water from the glass slide, 

 a fine streak upon the surface indicates its existence and position. 



These slender organs are variously arranged in different species of Infusoria. In 

 some they are extended in rows throughout the entire length of the animalcule, 

 and in others are distributed over the whole surface of the body. Fringes of cilia 

 encircle the mouths of some, while in many kinds, the circles of cilia forming into 

 bands, surround certain projections issuing from the upper part of the body. Nu- 

 merous species are furnished with only two of these filaments projecting from the 

 mouth, and nearly equal to the body in length. The base of each cilium terminates 

 in a bulb, and when the organ is in motion its point describes a circle, while the 

 globular base simply rolls round upon the surface to which it is attached. An idea 

 may be gained of this motion by holding the arm out stiffly and swinging it round, 

 so as to describe a circle in the air with the point of a finger ; the arm then corre- 

 sponds to one of the cilia, and the ball of the shoulder-joint to the bulb upon which 

 the cilium turns. The motion is doubtless performed by muscles, and Ehrenberg 

 considers that he has not only discovered their existence in some of the larger In- 

 fusoria, but also the arrangement of the fibres that compose them. 



The bands and coronets of cilia which encircle certain classes of animalcules 

 present, when in motion, a singular appearance. Though each organ is stationary 

 and revolves only around its bulb, yet the combined action of the circular rows is 

 such that they appear to revolve together, like a wheel upon its axle, and so com- 

 plete is the illusion that the name of wheel-animalcules, or Rotatoria, is given to 

 those which possess this peculiarity. 



Besides these organs, stiff hairs or bristles are found upon animalcules, which, 

 unlike the cilia, are devoid of rotation, but serve as supports to the body, and also 

 aid these living atoms in climbing. Animalcules are also found with hook-like pro- 

 jections extending from the under side of the body, which are capable of motion to 

 some extent, but do not possess the peculiar movement of the cilia. Many Infusoria 

 are also endowed with another kind of member, that more completely subserves 

 the purpose of motion, and which they have the power of protruding or withdraw- 

 ing at pleasure, as the snail extends and retracts its horns. These organs are soft, 

 and by some species can be thrust out from every part of the body; while in others, 

 that are partially covered by a shell, they are confined to the uncovered portions. 



The power of extension possessed by Infusoria over these organs is much 

 greater, in proportion to their size, than in the case of snails and animals of a 

 similar nature. 



In those Infusoria that are gifted with the highest organization, as the wheel- 

 bearing animalcules, there appears to be a member resembling a claw, by means of 

 which they attach themselves firmly to any object within their grasp. The claw 

 is appended to an extended portion of the body, resembling a foot. 



CLASSIFICATION. Dr. Ehrenberg divides this living world into two great classes, 



