PROTOZOA. 23 



has been caught, and is probably taken into the body 

 through the extension or flowing of the ectosarc over it. 



After the food is digested the excrement is sometimes 

 ejected simply by the unfolding of the protoplasmic body, 

 and at other times is discharged from the posterior part 

 of the body, as seen in fig. 5b. 



As already stated, the contractile vacuole is a cavity 

 which is filled with fluid and which contracts and dilates 

 quite regularly. According to the experiments of Grif- 

 fiths, 1 it performs at times an excretory function similar 

 to that of the kidneys in the more specialized animals, 

 but it is interesting to note that at other times no waste 

 nitrogenous matter is found in the vacuole, and it is most 

 likely, as stated by Griffiths, that the organ in its primi- 

 tive condition performs more than one kind of work, com- 

 bining, it may be, a respiratory with an excretory function. 

 Experiments on the more differentiated Protozoa, such as 

 Paramoecium and Vorticella, proved that the contractile 

 vacuole in these forms performed the function of a true 

 kidney, the product excreted being the same as in the 

 most specialized animals. 



Circulatory movements of the endosarc have already 

 been spoken of under the head of structure, and are men- 

 tioned here again since they belong with the physiological 

 activities of the Amoeba. PI. 9, fig. 8, represents the 

 granular endosarc flowing into the hyaline ectosarc, the 

 direction of the current being indicated by arrows. The 

 susceptibility of the organism to external forces is shown 

 in different ways ; whenever the glass slide on which the 

 Amoeba is crawling is touched or jarred, its pseudopodia 

 are partially or wholly drawn in and a more or less spher- 

 ical form is assumed, as seen in fig. g. 2 This irritability 



1 Proc. Roy. Soc. Edinburgh, XVI, iSSS-'Sg, p. 131. 



2 Amoeba radiosa. According to C. Scheel, Amoeba radiosa is the 

 young of A. proteus. See his Beitrage zur Fortpflanzung der 

 Amoben, in C. von Kupffer's Festschrift zum siebenzigsten Geburts- 

 tag, 1899, pp. 569-580. 



