in NUTRITION 267 



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 circulation 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 upon 

 as a potential anus, or aperture for the egestion of faeces or 

 undigested food-matters. It is a potential and not an actual 

 anus, because it is not a true aperture but only a soft place 

 in the cortex through which, by the contractions of the 

 medulla, solid particles are easily forced. 



Of course when Paramcecium ingests, as it usually does, 

 not carmine but minute living organisms, the latter are 

 digested as they circulate through the medullary protoplasm, 

 and only the non-nutritious parts cast out at the anal spot. 

 It has been found by experiment that this infusor can digest 

 not only proteids but also starch and perhaps fats. The 

 nutrition of Paramcecium is therefore characteristically 

 holozoic. 



It was mentioned above that the cortex is radially striated 

 in optical section. Careful examination with a very high 

 power shows that this appearance is due to the presence in 

 it of minute spindle-shaped bodies (A and B) closely arranged 

 in a single layer and perpendicular to the surface. These 

 are called trichocysts. 



When a Paramcecium is killed, either by the addition of 

 some poisonous reagent or by simple pressure of the cover 

 glass, it frequently assumes a remarkable appearance. Long 

 delicate threads suddenly appear, projecting from its surface 

 in all directions (c) and looking very much as if the cilia had 



