146 ZOOLOGY. 



the common stem. The first indication we can detect of 

 this new formation is a very slight movement in the 

 water, a little quivering around what we must yet call 

 the basal part. Presently there appear waved hairs, 

 which seem very flexible, and the motion of which re- 

 sembles that of a fringe of loose silk moved through the 

 water, an action very different from the regular waves of 

 perfect cilia. These waving hairs increase rapidly in 

 length, and in the vigour and rapidity of their undula- 

 tions, which gradually become decidedly rotatory, produc- 

 ing at length strong currents in the surrounding water, 

 and imparting a tremulous motion to the whole bell. 



"It is evident now that the separation is imminent, 

 for the minute point of connexion cannot long withstand 

 the rushing current of those rotatory paddles. At length 

 the bell suddenly shoots away, gliding with great swift- 

 ness through the water, borne by its numerous paddles, 

 and whirls about fora while in a headlong giddy manner. 

 At length it chooses a place of rest, becomes stationary, 

 fixes itself by that end which had formerly been the 

 mouth, but is now closed up, and presently begins to rise 

 by the development of a slender stalk which, though 

 minute at first, increases in length until it attains the 

 original dimensions." 



In reproduction by gemmation, the bell is not split in 

 two, a bud being produced near its extremity by the 

 expansion of the cortical layer. This bud is at first 

 nourished by the parent animal, but when it obtains its 

 circle of cilia it detaches itself, and swims about for a 

 time, then develops a stalk, and becomes fixed as before. 



213. At certain seasons the Yorticella coats itself with 

 a cyst (Gr. kustis, a bladder) of gelatinous matter, the 

 cilia and stalk disappearing. After a time the cyst 

 bursts, and a number of germs are set free, which, after 

 swimming about for a time, develop stalks and become 

 bell-animalcules like the original. This is denominated 

 reproduction by encystation ; whether it is sexual or 

 otherwise, has not been ascertained. 



