86 



MANUAL OF PHYSIOLOGY. 



FlG. 41. 



cesses (vibratile cilia), which constantly move in a certain direc- 

 tion, so as to propel the creature rapidly through the water. The 

 internal part of the cell is very soft, almost 

 fluid, and coarsely granular in appearance, con- 

 taining many bodies which have obviously been 

 introduced from without. This soft internal 

 protoplasm (endosarc) moves slowly round in 

 a definite direction, completing its circuit in 

 one or two minutes, and thus carries on a cir- 

 culation which mixes the various matters con- 

 tained in it. At one point of the ectosarc, or 

 cortical layer, an orifice or mouth leading to 

 an oesophageal depression is found. This ori- 

 fice is lined by moving cilia, which, by their 

 vibrations, drive the food into the oesophagus, 

 whence it is periodically jerked into the soft 

 internal protoplasm or endosarc, together with 

 some water, and thus forms a food vacuole, 

 which is carried round in the circulation of the' 

 ectosarc. Besides a well-marked nucleus and 

 nucleolus in the central part of the cell, these 

 paramcecia have one or more clear spaces 

 placed near the surface at the extremities of 

 the animal. These vacuoles suddenly contract, 

 and disappear every now and then. When this contraction 

 occurs fine canals radiating from the contractile vacuole are dis- 

 tended with the clear fluid which has probably entered the vacuole 

 from without. Thus a permanent set of water vessels carry fluid 

 from the contractile vacuole throughout the eudosarc. 



In such an animal there is a distinct advance of function com- 

 pared with the amoeba ; a more elaborate and specialized method 

 of feeding; a more systematic and regular circulation of nutri- 

 ent matters ; a respiratory distribution of water by the contrac- 

 tile vesicle and its water canals ; more rapid motion ; and more 

 obvious sensation. 



In the bell animalcule, or vorticella, the same kind of division 

 of labor exists, but in one of its commonest conditions it is at- 



Diagram of Par- 

 amoecium, showing 

 digestive cavity. 

 (a a) Body space 

 filled with soft 

 protoplasm, into 

 which food is 

 taken. (6) Mouth, 

 (c) Anus, (d) Con- 

 tractile vesicle. 

 ( After Lachmann.) 



