INFtrSCEIAL ANIMAICTJLES. 67 



which, under such circumstances, we may consider due to the exist- 

 ence of their eggs, upon, or about such vegetable matters, or to the 

 presence of the animals themselves in a dried state. 



The Rotatoria especially delight to live in still water, among 

 growing aquatic plants, such as Conferva, Letmia, Ccratophyllum, 

 Hottonia, «&c., to which they frequently adhere. They inhabit both 

 fresh and salt water, but are more numerous in the former. 



Immersion in water is, however, not necessary to their existence; 

 for they are to be found also in damp or moist earth, as in the 

 earthy deposit from the rain-water spouts of houses, in the detritus 

 of walls, roofs, &c., upon mosses and Lichens, such as the tufts of 

 Bryum, and about the mosses groT\dng on the roots of trees, such as 

 the Hypnum. From such plants as mentioned, they may be sepa- 

 rated, by washing with a little water. 



It is a curious fact, however, that they sometimes establish their 

 residence within the cells of mosses and Algae, where they are apt 

 to be made prisoners in the progress of growth of the plants. 



Their capability of being completely dessicated, and of being sub- 

 sequently revived, has been previously spoken of in Section VIII. 

 Ehrenberg has seen, in the Hydatina, life prolonged eighteen to 

 twenty days; but its duration will greatly depend on the circum- 

 stances of temperature, &c., imder which the Rotatoria are placed. 

 By far, the majority of Rotatoria have the power of locomotion, but 

 several genera form exceptions, their members mostly being fixed 

 by means of a conti'actile pedicle. 



These attached forms are enveloped by an outer tubular case, 

 within which, they can entirely withdraw themselves by means of 

 their pedicles, or, from which, they can extrude the greater part of 

 their body, when in search of food ; they thus enjoy a certain lati- 

 tude of motion, suitable to their peculiar condition. 



The locomotive Rotatoria, on the other hand, exhibit great activity 

 and variety in their movements. The greater number swim along 

 in a uniform manner, by means of the ciliated rotary organ ex. Bra- 

 chionus ; others, in addition, crawl like leeches, by alternately 

 advancing, and using as fixed points, the head and the suctorial 

 extremity of the tail, ex. Rotifer ; whilst a few skip or leap after 



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