1 6 PROTOZOA 



whether for assimilation, for accumulation, or for the direct 

 liberation of energy for the vital processes of the organism. 



Not only food from without, but also reserves formed and 

 stored by the protoplasm itself, must be digested by some zymase 

 before they can be utilised by the cell. In all cases of the 

 utilisation of reserve matter that have been investigated, it has 

 been found that a zymase is formed by the cell itself (or some- 

 times, in complex organisms, by its neighbours) ; for, after killing 

 the cell in which the process is going on by mechanical means 

 or by alcohol, the process of digestion can be carried on in the 

 laboratory.^ The chief digestion of all the animal-feeding Protista 

 is of the same type as in our own stomachs, known as " peptic " 

 digestion : this involves the concurrent presence of an acid, 

 and Le Dantec and Miss Greenwood have found the contents 

 of food-vacuoles, in which digestion is going on, to contain 

 acid liquid. The ferment- pepsin itself has been extracted by 

 Krukenberg from the Myxomycete, " Flowers of tan " {Fulign 

 varians,-p. 92), and by Professor Augustus Dixon and the author 

 from the gigantic multinucleate Amoeba, Pelomyxa ^palustins 

 (p. 52).'' The details of the prehension of food will be treated of 

 under the several groups. 



The two modes of Anabolism — true " assimilation " in the 

 strictest sense and " accumulation " — may sometimes go on con- 

 currently, a certain proportion of the food material going to the 

 protoplasm, and the rest, after allowing for waste, being converted 

 into reserves. 



Movements all demand catabolic changes, and we now pro- 

 ceed to consider these in more detail. 



The movements of an Amoeboid ^ cell are of two kinds : 

 " expansion," leading to the formation and enlargement of out- 



1 See Hartog, "On Multiple Cell-division, as compared with Bi-partition as 

 Herbert Spencer's limit of growth," in Kcp. Brit. Ass. 1896, p. 833; "On a 

 Peptic Zymase in Young Embryos," ibid. 1900, p. 786; "Some Problems of 

 Reproduction," ii. Quart. Journ. Micr. Sci. xlvii. 1904, p. 583. 



'■^ "On the Digestive Ferment of a large Protozoon." Ec2i. Brit. Ass. 1893, p. 801. 



■' See for studies of the movements of Protoplasm, Berthold, Frof.oplasmn- 

 i)ieclmnik (1886) ; Biitschli, Investigations on Microscojnc Foams and on Proto- 

 plasm, English ed. 1894 ; Verworn, General Physiology, 1899 ; Le Dantec, La Maiierc 

 Vivante, 1893 1 ; and Jensen, " Unters. ueb. Protoplasmamechanik," in Arcli. Cles. 

 Phys. Ixxxvii. 1901, p. 361 ; Davenport, Experimental Morpiliology, i. 1897 ; H. S. 

 Jennings, Contr. etc. 1904. 



