PROTOZOA. 15 



It may be that, in the earliest condition of living pro- 

 toplasm, nourishment was simply taken into the mass by 

 a process analogous to absorption, and that the additional 

 strength acquired in this way, together with a subsequent 

 deficiency in the food supply, gave rise to a desire to go 

 in search of food and therefore originated the function of 

 locomotion. In the development of the more specialized 

 animals the. passive, absorbent stage is not represented, 

 so that the function of locomotion precedes the function 

 of taking and digesting food. 



The function of reproduction is shown in PL i, figs. 

 4-6a, also in PL 2, rigs. 3~4a. The body becomes con- 

 stricted (PL i, fig. 4), and this constriction continues un- 

 affected by the change in form which each of the halves 

 undergoes until only a mere thread connects the two 

 parts (PL i, fig. 5 ; PL 2, fig. 3) ; this finally separates 

 and each half rounds itself off immediately and creeps 

 away as an independent organism (PL i, figs. 6, 6a ; PL 

 2, figs. 4, 4a). This process of reproduction is known as 

 division or fission. It will be noticed that the two youth- 

 ful forms resemble the parent before constriction of its 

 body has taken place. 



We cannot fail to recognize in Protamoeba an organism 

 performing the important vital functions of the more spe- 

 cialized animals. We shall presently see how this knowl- 

 edge of its life history is a natural introduction to the 

 more differentiated Amoeba (PL 9), which is regarded by 

 all biologists as an animal; and for this reason we prefer 

 to place the Protamoeba among animals rather than 

 among plants or neutral organisms. 



Portions of the sea bottom at great depths are covered 

 by a vast gelatinous mass known as the Bathybius slime. 

 This slime is, in part, made up of an infinite number of 

 protoplasmic cytodes of various sizes, and imbedded in 

 these are calcareous bodies called coccoliths, which are 

 now considered to be vegetable in origin and therefore 

 foreign to the true Bathybius. 



