414 



MICROSCOPIC FORMS OF ANIMAL LIFE. 



or when its cavity lias been distended by the ingestion of any 

 substance above the ordinary size. The body does not seem to 

 possess much contractile power in its own substance, its move- 

 ments being principally executed by the instrumentality of loco- 

 motive appendages ; one remarkable instance of contractility, 

 however, is presented by the stalk of Vorticella ( 268). The 

 locomotive appendages, which may all be considered as prolon- 

 gations of the tegumentary layer, are destitute of any more 

 minute organization, being, in fact, of the nature of cilia, though 

 sometimes of much larger dimensions, and employed in a dif- 

 ferent manner. The vibration of ciliary filaments, which are 

 either disposed along the entire margin of the body, as well as 

 around the oral aperture (Figs. 194, 195), or are limited to some 

 one part of it, this being always in the immediate vicinity of the 



FIG. 194. 



Fia. 195. 



Fig. 194. Kerona stturus : a, contractile cavity; 6, mouth; c, c, animalcules swallowed by the 

 Kerona, after having themselves ingested particles of indigo. 

 Fig. 195. Paramecium caudatum: a, a, contractile cavities; 6, mouth. 



mouth (Fig. 196), is the means by far the most frequently em- 

 ployed by the beings of this class, both for progression through 

 the water, and for drawing alimentary particles into the interior 

 of their bodies. In some their vibration is constant, whilst in 

 others it is only occasional, thus conveying the impression that 

 the Animalcule has a voluntary control over them ; but there is 

 strong reason for questioning the existence of any such self- 

 directing power. These cilia, like those of the zoospores of 

 Protophytes, can usually be distinctly seen only when their move- 

 ment is very much slackened in its rate, or when it has entirely 

 ceased. Sometimes, however, instead of a multitude of short 

 cilia, we find a small number of long slender filaments, usually 

 proceeding from the anterior part of the body (that nearest the 

 mouth), and strongly resembling the elongated cilia of Proto- 

 coccus (Fig. 68, H), or of Volvox (Fig. 70, i, K, L). But in other 



