PAKAMCECIUM. 11 



lets are forced, by the contractions of the body, out of the 

 inner end of the tube into the endosarc. 



e. One of the pellets, together with a little water swal- 

 lowed with it, forms a food vacuole, of which several (Fig. 

 2, g) may usually be seen in different parts of the body. 

 A food vacuole is a spherical space filled with water, and 

 containing solid particles of various kinds. As the vacu- 

 oles are carried around the body by the circulation of the 

 endosarc, the water and soluble parts are digested out, 

 until at last only the indigestible parts remain embedded 

 in the sarcode as a food ball (Fig. 2, z). 



f. The anus. After a time these particles accumulate at 

 a point (Fig. 2,/ 1 ) upon the dorsal surface about halfway 

 between the vestibule and the posterior end of the body. 

 The ectosarc becomes thin over them, and they are then 

 driven out of the body through a temporary anus, the 

 location of which is permanent. 



VIII. The contractile vesicle. If a specimen which is 

 pretty quiet be carefully watched, a large transparent 

 space will be seen at some point in the body, and after 

 remaining visible for some twenty or thirty seconds, it 

 will suddenly disappear and gradually reappear. In some 

 species there is one near each end of the body (Fig. 2, 

 b and c), and in others only one, near the middle. When 

 they first appear they are very small ; they gradually in- 

 crease in size until they are quite conspicuous, as shown 

 at c in Fig. 2. Uadiating channels then make their ap- 

 pearance and extend from the vesicle into the surround- 

 ing endosarc. The vesicle now suddenly contracts and 

 disappears, its contents being forced into the tubes, which 

 are visible for a short time longer, as at b in Fig. 2, and 

 then gradually disappear also. In a few seconds the vesi- 

 cle reappears at the same place. 



