STIMULI AND THEIR ACTIONS 



387 



undisturbed, and their protoplasm flows slowly but constantly 

 without exception in a centripetal direction. But, if the shaking 

 be more intense, they assume a varicose appearance, their centri- 

 petally streaming protoplasm collecting into many small spindles 

 and globules, of which the smaller flow into the adjacent larger 

 ones, while the larger ones constantly approach the central 

 protoplasmic body; upon long-continued action all protoplasm 

 flows into the cell-body. 1 This curious formation of droplets 

 upon pseudopodia is a peculiarity of strongly and continually 

 stimulated protoplasm which is general in Rhizopoda that are 

 provided with filose pseudopodia ; it is only a special case of the 

 general law that strong stimuli cause naked protoplasmic masses 



FIG. 180. Orbitolites. A part of the surface of the shell, with extended, thread-like pseudopodia. 

 A, Unstimulated ; B, after vigorous shaking. 



to assume the spherical form. The same tendency toward the 

 formation of globules, which all stimulated protoplasm as a whole 

 shows, is also noticeable in its individual parts. 2 



Ciliary motion is increased greatly by rhythmically inter- 

 mittent shocks, so that Infusoria stimulated in this way rush 

 madly through the water for a considerable time after the 

 stimulation has ceased. A real tetanus, however, in which the 

 cilia remain bent in the position of contraction, appears not to 

 occur, at least thus far such has not been observed. The 

 rhythmic motion of the cilia continues, and is changed in its 

 rate and amplitude only. 



1 Of. Verworn('92,l). 



2 Gf. herewith the phenomena of necrobiosis, p. 329, Fig. 142. 



C C 2 



