TRICHOCYSTS in 



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 Paramoecium 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 

 starch is probably converted into dextrin, a carbo-hydrate 

 having the same formula (C 6 H 10 O 5 ) but soluble and 

 diffusible. Oils or fats seem to be partly converted into 

 fatty acids and glycerine. The nutrition of Paramoecium is 

 therefore characteristically holozoic. 



It was mentioned above (p. 108) that the cortex is ra- 

 dially striated in optical section. Careful examination with 

 a very high power shows that this appearance is due to the 

 presence in the cortex of minute spindle-shaped bodies (A 

 and B, trcJi) closely arranged in a single layer and perpen- 

 dicular to the surface. These are called trichocysts. 



When a Paramoecium is killed, either by the addition of 

 osmic acid or some other poisonous reagent or by simple 

 pressure of the cover glass, it frequently assumes a remark- 

 able appearance. Long delicate threads suddenly appear, 

 projecting from its surface in all directions (c) and looking 

 very much as if the cilia had suddenly protruded to many 

 times their original length. But these filaments have really 

 nothing 'to do with the cilia; they are contained under 

 ordinary circumstances in the trichocysts, probably coiled up ; 

 and by the contraction of the cortex consequent upon any 

 sudden irritation they are projected in the way indicated. 



