i THE PROTOZOA 15 



water, which is driven down the gullet, and small globules of 

 water containing food particles pass into the protoplasm, 

 forming small vacuoles, inside of which the food is digested. 

 These vacuoles pass through the protoplasm, and finally once 

 more reach the gullet, into which any indigestible particles 

 are ejected, to be carried away by the water. 



Here, as in Amoeba, there is a large contractile 

 Excretion. ', ,. ' . , ,. . , 



vacuole, by means of which liquid excreta are got 



rid of. The process of Respiration takes place over the whole 

 surface of the body. 



Response Vorticella is exceedingly sensitive to any con- 

 to Stimuli, tact -stimulus ; directly it is touched, the bell 

 Movement, contracts,' drawing down its disc and cilia, and 

 becoming almost globular; at the same time, the stalk con- 

 tracts into a tight spiral (Fig. 4, B) t thus bringing the bell close 

 down to the object to which the stalk is attached. The 

 power of contractility of the stalk is concentrated in a special 

 strand of protoplasm, that can be seen in the extended stalk, 

 running round inside the cuticle in a very open spiral (Fig. 

 4, A). On contraction, this fibre becomes much shorter and 

 thicker, thus drawing the coils of its spiral close together, and 

 throwing the elastic cuticle into corresponding folds (Fig. 4, B). 

 Such a differentiated portion of protoplasm, having this 

 power of contracting in a definite direction, causing definite 

 movements of the body attached to it, is essentially a muscle, 

 so that the " contractile axial fibre " of the stalk may be 

 looked upon as a foreshadowing of the muscular system 

 which becomes so complex in higher animals. 

 Eeproduc- As in Amoeba, Vorticella can reproduce by the 

 tion. simple fission of the body into two, the cleft 

 beginning at the 

 free surface, and 

 spreading down- 

 wards to the base 

 of the bell ; the 

 fission does not, E 



however, involve FIG. 6. Vorticella. (After Saville Kent. ) 



the Stalk. One of EI, The beginning of binary fission of a bell ; BJ2, com- 

 the two daughter pletion of the process ; E3, the barrel-shaped new 



bells, Whilst Still ^dual swimming away. 



attached to the parent stalk, develops a circlet of cilia near its 



