2] 



EFFECT OX METABOLISM AXD MOVEMENT 



101 



the thick region, together with all the proximal lying proto- 

 plasm, begins to flow towards the centre. The whole plasma 

 thread retracts. 



Again, if an individual of Difflugia (Fig. 15) be slightly 

 shaken, the pseudopodium contracts into the shell ; if it be 



FIG. 14. Cyphoderia margaritacea, showing the retraction of its pseudopodium as a 

 result of irritation at the point indicated by the arrow. (From VERWORN, '921) 



FIG. 15. Difflugia urceolata ; at a, stimulated by a weak local irritation ; at 6, by a 

 somewhat stronger one. (From VERWORN, '89.) 



violently shaken, the following changes occur : drops of a less 

 highly refractive substance seem to gather on the surface of 

 the filamentous pseudopodium and unite to form a sheath sur- 

 rounding a more highly refractive axis. At the same time, 

 axis and sheath retreat into the central mass. In this case, 

 then, we have a segregation of dissimilar protoplasmic sub- 

 stances, and a tendency to collect about centres along the 



