10 



OUTLINES OF NATURAL HISTORY. 



rounding water, and particles of food are brougiit to the 

 mouth of the animal. 



Fig. 2. — A, Paramcecium, sliowing the " cilia " covering tlie surface, and tlie 

 rudimentary organs of circulation (u v). B, Tlie same, di\'iding trans- 

 versely into two halves. C, The same, dividing longitudinally. 



Immediately within the delicate external membrane 

 which cover.s the body, is a layer of "a firmer and more 

 consistent character ; and this, in turn, gradually melts 

 into a soft, semi-fluid central mass, which constitutes the 

 greater portion of the body, and which contains numerous 

 small solid particles floating in it. 



The animal is provided -with a distinct mouth, and a 

 short, funnel-shaped gullet, but the mouth does not open 

 into a stomach, or even into a distinct body-cavity. 

 Hence the food simply passes through the mouth into 

 the semi-fluid central substance of the body, and the in- 

 digestible parts of it are expelled by a second oldening 

 placed near the mouth. 



The most important internal organs, and indeed almost 

 the only ones, are one or two little chambers (fig. 2, A, v v), 

 which open and shut at regular intervals, perhaps five or 

 six times in a minute, and which appear to drive the 

 fluid which they contain through all parts of the body. 



