THE INFUSORIA. 



certain radiating canals, which extend from the cavities mtQ the 

 surrounding sarcode, and disappear again before diastole occurs? 

 There is no doubt that the clear space is a chamber filled with 

 fluid in the cortical layer ; and since good observers maintain that 

 there is an aperture of communication, through the cuticula, 

 between the ' contractile chamber ' and the exterior, this fluid 

 can be little more than water. Perhaps the whole should be re- 

 garded as a respiratory or secretory mechanism : in one shape or 

 another, it is eminently characteristic of the Infusoria. Besides 

 this singular apparatus, there lies embedded in another part of 

 the cortical layer a solid mass, of an elongated oval shape (Fig. 

 5, A, B, d), which has been called the " nucleus," though it must 

 be carefully distinguished from the " nucleus " of a cell. Upon 

 one side of this, and, as it were, stuck on to it, is a little rounded 

 body (Fig. 5, B, d'), which has received the name of the 

 " nucleolus." The animal swims about, driven by the vibration 

 of its cilia, and whatever nutriment may be floating in the water 

 is appropriated by means of the current which is caused to set 

 continually into the short gullet by the cilia which line that 

 tube. 



But it is a singular circumstance, that these animals have an 

 alimentary canal consisting of a mere gullet, open at the bottom, 

 and leading into no stomach or intestine, but opening directly 

 into the soft central mass of sarcode. The nutritious matters 

 passing down the gullet, and then into the central more fluid sub- 

 stance, become surrounded by spheroids of clear liquid (Fig. 5, 

 A, d), consisting apparently of the water swallowed with them, so 

 that a well-fed Paramoecium exhibits a number of cavities, each 

 containing a little mass of nutritious particles. Hence formerly 

 arose the notion that these animals possess a number of stomachs. 

 It was not unnaturally imagined that each of the cavities in 

 question was a distinct stomach ; but it has since been dis- 

 covered that the outer layer of the sarcode is, by means of some 

 unknown mechanism, kept in a state of constant rotation; so 

 that the supposed stomachs may be seen to undergo a regular 

 circulation up one side of the body and down the other. And 

 this circumstance, if there were no other arguments on the same 

 side, is sufficient to negative the supposition that the food- 



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