INFUSORIAL ANIMALCULES. 



43 



PURSE ANIMALCULE. A species of this animalcule is represented in figure 58. 



Its body, which is white and round, is covered with cilia, 

 arranged in circular rows, and the double fringes that sur- 

 round the large opening which constitutes its mouth are 

 longer than the rest. Its stomachs, which resemble in 

 shape small purses, are not connected together in a chain ; 

 but are attached to the interior of the animalcule, by slen- 

 der stems. These Infusoria are found with the dust-monad 

 and tablet-animalcules, which they devour in great num- 

 bers, and in the specimen delineated, several of these crea- 

 tures are seen within its body. The natural length of this 

 species of purse-animalcule is one-one hundred and " 

 of an inch. 



Fi. 58. 



WHEEL-ANIMALCULES, OR ROTATORIA. 



These interesting animalcules, of which there is a great variety, constitute one 

 of the great classes into which the Infusorial world is divided. They live, for 

 the most part, in water ; but it does not appear to be necessary to their existence 

 that they should be enveloped by this fluid. They are frequently found to reside 

 in moist earth, and some species are known to dwell in the cells of mosses and 

 sea-weed. We have already observed that these Infusoria have received their 

 name from the apparent revolution of their crowns of cilia, and that in addition 

 to this marked peculiarity, they are distinguished from the Polygastric animal- 

 cules by possessing a single stomach, and in being furnished, for the most part, 

 with jaws and teeth. The Rotatoria, though endowed with the power of chang- 

 ing the shape of their bodies, by contraction and expansion, cannot do so by the 

 growth of buds, or self-division, like many kinds of the first class. At the lower 

 extremity of the body is a short stem, or tail, by which the animalcule fastens 

 itself to some fixed object, at its pleasure, and thus prevents the upper part of 

 the body from partaking of the motion of the cilia. This class of Infusoria are 

 viviparous* and also multiply from eggs, which, in some species, are equal in 

 length to one-third of the extent of the body. For an unknown period of time, 

 the eggs retain the living principle within them, exposed to heat and cold, to 

 moisture and to drought: they are borne upon the wings of the wind, over sea and 

 land, bursting into life, and filling the water with their swarming multitudes, 

 whenever a concurrence of circumstances favorable to their development calls 

 them into existence. Nor is this tenacity of life confined to the egg ; the ani- 

 malcule itself, as we have previously shown, slumbers for months, in apparent 

 death, and is repeatedly revived. 



* Producing young in a living state. 



