THE SLIPPER ANIMALCULE. 21 



balls and minute fat globules, and various foreign bodies 

 that have been swept into the mouth with food. The feed- 

 ing habits of the animal are best studied after putting 

 some finely powdered carmine or indigo into the drop of 

 water with it. Bits of these indigestible substances will 

 be seen swept along the groove by its cilia, through the 

 mouth, if they be small enough, for this is the only 

 entrance requirement, and down a sort of short rudimen- 

 tary esophagus, at the bottom of which they collect into 

 a little pellet before being ingulfed by the protoplasmic 

 mass of the interior. Then they may be seen to circulate 

 slowly about the body, and, after considerable time, to 

 collect at a point about halfway between the mouth and 

 the posterior end of the body, where they are egested 

 directly through the body wall. 



The Life Process. This is essentially as in amoeba ; 

 but there are some interesting differences in its details. 



When any part of an animal becomes so modified as to 

 be better fitted for doing some one thing, that part is said 

 to be specialized. Thus in paramecium the cilia are 

 specialized for locomotion. One circlet of cilia that 

 fringing the groove leading to the mouth is still more 

 highly specialized for setting up currents in the water as 

 a means of capturing food. A mouth and short esophagus 

 are specialized for receiving food, and contractile vesicles 

 are specialized for circulating the fluids of the body. Every 

 time a vesicle contracts, it drives its liquid contents out into 

 the surrounding body mass. These specialized parts in the 

 one-celled paramecium foreshadow the locomotor, digest- 

 ive, and circulatory systems of the many-celled animals. 



Amceba and paramecium are representatives of the Pro- 

 tozoa, a large group of microscopic unicellular animals of 

 wide distribution. 



