i io PARAMCECIUM, STYLONYCHIA, AND OXYTRICHA 



into the vacuole, and finally discharged into the surrounding 

 medium. 



The process of feeding can be very conveniently studied 

 in Paramcecium by placing in the water some finely-divided 

 carmine or indigo. When the creature comes into the 

 neighbourhood of the coloured particles, the latter are swept 

 about in various directions by the action of the cilia : some 

 of these are however certain to be swept into the neighbour- 

 hood of the buccal groove and gullet, the cilia of which all 

 work downwards, i.e. towards the inner end of the gullet. 

 The grains of carmine are thus carried into the gullet, where 

 for an instant they lie surrounded by the water of which it is 

 full : then, instantaneously, probably by the contraction of 

 the tube itself, the animalcule performs a sort of gulp, and 

 the grains with an enveloping globule of water or food-vacuole 

 are forced into the medullary protoplasm. This process is 

 repeated again and again, so that in any well-nourished 

 Paramoecium there are to be seen numerous globular spaces 

 filled with water and containing particles of food or in the 

 present instance of carmine or indigo. At every gulp the 

 newly formed food-vacuole pushes, as it were, its predecessor 

 before it : contraction of the medullary protoplasm also takes 

 place in a definite direction, and thus a circulation of food- 

 vacuoles is produced, as indicated in Fig. 21, B, by arrows. 



After circulating in this way for some time, the water of the 

 food-vacuoles is gradually absorbed, being ultimately excreted 

 by the contractile vacuoles, so that the contained particles 

 come to lie in the medulla itself (refer to figure). The circu- 

 lation still continues, until finally the particles are brought to 

 a spot situated about half-way between the mouth and the 

 posterior end of the body : here if carefully watched they 

 are seen to approach the surface and then to be suddenly 

 ejected. The spot in question is therefore to be looked 



