STIMULI AND THEIR ACTIONS 



363 





long finger-shaped pseudopodia by the fact that drop-like projec- 

 tions form on the surface of the pseudopodial plasma, beginning at 

 the place of stimulation. If such a pseudopodium be stimulated only 

 slightly at the tip by contact with a needle, the reaction extends a 

 short distance only, the surface of the pseudopodium becoming 

 slight!} 7 " undulating (Fig. 156, a). But if it be stimulated more 

 strongly, the reaction is 

 stronger and is transmit- 

 ted considerably farther 

 (Fig. 156, b). The re- 

 action diminishes in extent 

 as the distance from the 

 place of stimulation in- 

 creases, and finally it is 

 extinguished. 1 Very slight 

 conduction is found in 

 many rhizopods that have 

 thread-like pseudopodia, 

 e.g., OrUtolites (Cf. Fig. 98, 

 p. 238). Here even with 

 the strongest stimulation, 

 such as cutting across a 

 pseudopodium, the excita- 

 tion is limited to the im- 

 mediate vicinity of the 

 place stimulated, the pro- 

 toplasm there being drawn 

 together into one or more 

 small globules. These 

 globules glide centripetally 

 for a very considerable dis- 

 tance along the pseudo- 

 podial thread, which thus 

 begins to shorten, while 



the globules gradually dis- Fio.l^.-Difflugiaurceolata. Three finger-shaped, hyaline 



Solve and allow their Sub- pseudopodia are projected out of the urn-shaped shell 



n . , made of sand-grains. At a feebly stimulated locally, 



Stance tO DOW into the at & somewhat more strongly stimulated. 



central body (Fig. 157). 



Their movement is not to be regarded as a conduction of the 

 excitation, 2 but only as the expression of the transport of sub- 

 stance by the stimulated protoplasmic mass to the cell-body ; for 

 the protoplasm in the vicinity of the globules exhibits no pheno- 

 mena of excitation, but streams on quietly in a centrifugal direction. 



1 Cf. Verworn ('89, 1). 



2 In the first edition of this book this was so regarded; but later studies upon 

 the Rhizopoda of the Red Sea have convinced me that conduction of excitation 

 and transport of substance are to be separated from one another in naked proto- 

 plasmic masses. Cf. Verworn ('96, 3). 



