300 



ELECTRO-PHYSIOLOGY 



CHAP. 



body, while the entire pseudopod was gradually withdrawn. 

 Since we shall frequently have occasion to refer to these rhizo- 

 pods (which are exceptionally well adapted to electrical excita- 

 tion experiments) it is advisable here to introduce some further 

 remarks as to their structure. The fairly large globular body of 

 Actinosphaerium exhibits two distinct layers a darker, central, 

 richly nucleated mass (endoplasm), and a lighter, vacuolated. 

 cortical layer (Fig. 97). Each vacuole is filled with fluid, 

 bounded by a wall of homogeneous, finely granular protoplasm : 



H-- 



FIG. 97. Actinosphcerium cichorne. Polar effects of excitation with passage of a constant 



electrical current. (Venvorn.) 



this same protoplasm forms part of the bristle-shaped pseudopodia 

 which stand out from the body in all directions, and exhibit a 

 characteristic differentiation of structure an " axial ray " of firmer 

 consistence covered by the somewhat fluid protoplasm like a rind. 

 The contraction phenomena described by Ivtihne manifest them- 

 selves in a constant manner to a given mode of excitation. " In 

 consequence of stimulation the axial ray of a pseudopod in the un- 

 excited state of almost homogeneous enveloping protoplasm, gathers 

 itself together, while streaming towards the body upon the axial ray, 

 in small, solitary, fusiform or globular varicosities, between which 



