INFUSORIA. 409 



of various forms and stages of growth, represented in 

 fig. 217. 1 



Ehrenberg included in his family of Infusoria, Rhizop- 

 oda, Unicellular, and other Algse, embryonic forms, and 

 Rotifers. Most naturalists, however, now admit that the 



Fig. 217. — Noctiluca miliaria. 



organization of the Rotifers is of a far higher nature than 

 had been suspected by Ehrenberg ; and some assert that 

 their proper place in the classification of animals is the 

 annulose sub-kingdom ; the true nature of many of the In- 

 fusoria is still a disputed question. In outward form they 

 may be said to vary almost indefinitely ; but anatomically 

 their bodies should be regarded as consisting of three dis- 

 tinct structures. The cuticle or integument (" pellicula " of 

 Carter), on which are borne the cilia and other locomotive 

 apparatus ; the cortical layer or parenchyma of the body 

 (" diaphane " of Carter) ; and the chyme mass, occupying 

 the abdominal cavity, or interior of the body (sarcode or 

 " abdominal mucus " of Carter), within which the par- 

 ticles of food rotate. The term "ventral" is usually ap- 

 plied to that side of the body on which the mouth is 

 placed. 



In the well-known Paramcecium we have the true and 

 most widely distributed type of the Infusoria. The 

 general structural character of this minute animal is 

 common to the species ; indeed, its structural features may 

 be accepted as a fair definition of the whole group. The 

 Paramcecium is surrounded on its external covering by 

 cilia, wbich are constantly in action, and enable it to move 

 about in its watery element in a most remarkably active 

 manner. At one point the body appears to be slightly 



(1) See Gosse's Naturalist's Rambles : Huxley, Micro. Journal, 1855. 



