PRIMARY FUNCTIONS OF THE ORGANISM 33 



described a more or less permanent pseudopodium 

 which extends from one edge of the cell-body 

 freely into the water " and waves back and forth, 

 serving as a sort of feeler or antenna." l In yet 

 another form, Masti- 

 gamceba, there is a per- 

 manent lash or flagellum 

 projecting from one por- 

 tion of the body, the 

 rest of the creature .re- 

 taining " amoeboid " 

 movements. In the 

 group of Protozoa called 

 " Flagellate," the ame- 

 boid habit is not found, 

 but the animal moves 

 very swiftly by the 

 lashing of one or more 

 permanent whiplike fla- 

 gella. In these three 

 types we see three dif- 



J L f, flagellum ; p, pseudopodium. 



ferent grades of Special- (From Calkins, after Schultze.) 



FIG. 11. Mastigamceba aspera: 



1 In the comparisons that follow, the reader must not understand that 

 one type has been transformed into another in any way whatever. 

 The different steps have been arranged side by side much as one might 

 form an exhibit of different models of the telephone or the phonograph 

 from the first crude type to the modern improved machine. In one 

 sense, though not in a material or genetic sense, the perfected phono- 

 graph has been derived from the earlier model. In the case of specializa- 

 tion of cells, however, as we shall see from the consideration of differ- 

 entiation in development there is often a very direct genetic relationship 

 between cells of a specialized type and those of the most generalized 

 types. 



D 



