18 VIEWS OF THE MICROSCOPIC WORLD. 



is the most remarkable, and is common to all Infusoria, is a slender filament like 

 a hair, situated near the mouth, and from its striking resemblance to an eye-lash 

 is known by the name of cilium, the Latin word for eye-lash. 



The cilium is employed by the animalcule for the purpose of motion, and also 

 for that of procuring food. Using this member as an oar, the creature moves 

 swiftly through the water, and so curious is the action of this propeller, that the 

 very stroke which effects a progressive motion, causes at the same time a current to 

 set towards the mouth of the animalcule, bearing its prey and food within its reach. 



In addition to the offices of the cilia* just described, they are supposed by some 

 naturalists to be the principal instruments for respiration to the Infusorial world ; 

 inasmuch as similar appendages are found encircling the gills or beard of the 

 oyster and muscle, and other animals of the like nature. It is by means of the 

 gills that these creatures inhale the air contained in the water, and the cilia by 

 causing currents to 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 per- 

 formed." 



When an animalcule is examined, this delicate member easily eludes observa- 

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

 mine, 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 animal- 

 cule, 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. Numerous 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 corresponds 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 Infusoria, but also the arrange- 

 ment 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 



* Cilia, the plural of cilium. 



