THE VORTICELL^. 45 



projecting. From the middle of the under part^ a long 

 tendril, or spirally contractile pedicle, or stalk, proceeds, 

 and is fixed to a common base, with numerous other in- 

 dividuals, — the whole forming a group, or cluster. The 

 size of the body, without the stalk, is about one twenty- 

 fourth of a line. The pedicle by which the body is 

 fixed to its position, is furnished with a long muscle, by 

 means of which it can be suddenly contracted into a 

 spiral coil, apparently at the will of the animal, (pi. iii, 

 fig. 3); the Vorticella has thus considerable latitude of 

 motion, though restrained within the limits of its tether. 

 This contractile action is continually going on, — now 

 in one or two individuals only, then in several; and 

 often the whole group suddenly shrinks down into a 

 confused mass, and the next instant expands, and every 

 little bell becomes fully developed, with its cilia in rapid 

 oscillation. 



YoRTICELLiE FED WITH CARMINE, (pi. IH, figS. 1, 2, 



3, 4, 6). The circular eddies, or whirlpools, produced 

 in the surrounding fluid by the zones of cilia are visible 

 in ordinary conditions; but they are rendered much 

 more distinct if a few particles of colouring matter are 

 introduced into the water; and by this means another 

 interesting part of the structure of these animalcides 

 is made manifest. Let us try the experiment. I place 



