5 66 



THE LOWEST ANIMALS. 



ROSEL's trumpet-animalcule, Stentor (magnified 200 diameters). 



oral cilia set up currents which 

 converge to the mouth -funnel, 

 and carry in other infusoria, 

 diatoms, <'tc. 



The bell-animalcules usually 

 possess stalks, and are either 

 solitary or form branching colo- 

 nies. Vorticella, whose outline 

 is like that of a wine-glass, is 

 provided at the rim with an 

 incomplete circlet of cilia, one 

 end of which passes down into 

 the mouth-funnel at the margin 

 (r) of the disc; the stalk con- 

 tains a contractile band (m) 

 which produces a rapid jerking 

 motion by throwing the stem 

 into coils ; in the body-mass lie 

 the nucleus (n) and contractile 

 vacuole (v). Reproduction takes 

 place by transverse division into 

 two. Ehrenberg observed twelve 

 individuals to originate from one 

 within twenty - four hours, so 

 that, calculating on this basis, 

 one million individuals would be 

 produced within twenty days. 

 The common-branched bell-ani- 

 malcule (Carchesium) divides 

 more rapidly, namely, once in an 

 hour; each again being soon 

 ready for division, so that one 

 thousand could arise in ten hours, 

 and a million in twenty hours ; 

 but, as a matter of fact, only 

 two hundred have actually been 

 observed to have been formed in 

 one day, owing to the intervals 

 between successive divisions be- 

 coming longer. The vigour of 

 the exhausted stock becomes 

 rejuvenated, however, by the 

 fusion or conjugation of two 

 individuals into one. 



The nodding bell-animalcule 

 (Epistylis) forms little branching 



