ANIMALCULES. 



721 



The Ciliated Infusorians are classed according to the arrangement of their 

 cilia. These sometimes cover the whole surface of the body, as in the 



Slipper animalcule (Fig. 8, A), 

 which is very common in pond 

 water or in infusions of hay, and 

 measures from 

 inch in length, 

 the distinction 



A 3 



Fig. 8. CILIATED INFUSORIA. 

 A, Paramoecium. 

 JS, Stentor. 



g to ih of an 

 In this Protozoan, 

 between the outer 

 part of the body and the inner 

 granulated part is very clear, and 

 the mouth and tube leading from it 

 are very evident. In the outer 

 "skin" a number of small oval 

 bodies can be seen pointing out- 

 wards. These, which are known as 

 trichocysts, are minute bags contain- 

 ing threads which can be shot out 

 of them and are probably used as a 

 defence against enemies. These 

 structures recall the stinging threads 

 of the Coelenterates, but are still 

 more wonderful as the products of a 

 single cell. 



In the next division of the 

 Ciliated Infusorians, very fine cilia 

 cover the surface of the body, while 

 longer ones encircle the mouth. The Trumpet animalcules (Fig. 8, B), 

 usually about $ of an inch in length, are found moving about freely in 

 the water or attached, either singly or in groups, to some submerged 

 object by the narrowed end of the body. The 

 lower part of the body is sometimes protected 

 by a kind of sheath or case. The wide opening 

 at the free end which surrounds the mouth is 

 fringed with long and strong cilia. In order to 

 multiply, these Trumpet animalcules divide into 

 two, a new mouth and oral fringe forming on the 

 parent animal before division. 



The Infusorians of the next division have smooth 

 bodies, the cilia being usually confined to the 

 region round the mouth ; in some cases, how- 

 ever, a second band of cilia surrounds some other 

 part of the body. Some of the attached Infusorians 

 of this kind surround themselves with a slipper- 

 shaped case of protoplasm, which helps to protect 

 the soft part of the body, and can, when necessary, almost entirely cover it. 

 As a rule, however, the mouth end, with its circle of cilia, protrudes from 

 the aperture of the case in search of food. Other forms attach themselves 

 by stalks which are contractile, and can, by coiling up spirally, quickly with- 

 draw the animal from any threatening danger. 



The Bell animalcules, when watched under the microscope, afford a very 

 interesting example of the complexity of life and movement which may be 

 attained by the single cell. When the water in which they are is. for any 

 47 



Fiff,9. GROUP OP BFMJ 

 ANIMALCULES (V orticellidae). 



