4] TOXQTAXIS 89 



density of the salt solution in which it has been reared. Finally, 

 MASS ART has shown, by a new method, that several soluble 

 organic compounds can permeate the bounding cell-film of 

 Flagellata. Thus, if after permanently plasmolyzing Polytoma 

 uvella by a 0.02 MW % solution of KNO 3 , a 0.01 MW % solu- 

 tion of saccharose be added to the solution, the protoplasm soon 

 regains its normal form, apparently by absorption of saccharose, 

 since the cell- wall is impermeable to KXO 3 . By the same 

 method, potassium acetate, calcium butyrate, calcium phosphate, 

 glycerine, ammonium tartrate, asparagine, glycose, sodium 

 benzoate, salicin, and phloridzin can be shown to permeate the 

 protoplasm of this flagellate. All these facts point to the con- 

 clusion to which physicists had arrived concerning dead animal 

 membranes, that protoplasm admits the slow penetration of the 

 dissolved salts, and thus effects the eventual equilibration of 

 internal and external densities. 



In conclusion, a word may be said concerning variability in 

 capacity of acclimatization. The data afforded upon this sub- 

 ject by RICHTER ('92) are the most valuable. He was able to 

 acclimatize Tetraspora to 16% (0.27 MW %) NaCl, while 

 Spirogyra would not withstand, under like treatment, 0.5% 

 (0.0085 MW %). It is clear then that, just as the resistance 

 capacity varies, so also does the acclimatization capacity. 



4. CONTROL OF THE DIRECTION OF LOCOMOTION BY 

 DENSITY : TONOTAXIS 



Three authors only, so far as I know, have concerned them- 

 selves with this phenomenon, STAHL ('84), PFEFFER ('84, '88), 

 and MASS ART ('89, '91). STAHL ('84) observed that plasniodia 

 of Myxomycetes withdrew from solutions either denser or less 

 dense than the normal, and concludes that the action is not a 

 simple, directly explicable one, but is rather a highly compli- 

 cated irritability phenomenon. The observations of PFEFFER 

 were incidental to his study of chemotaxis. He found that 

 high concentrations of many substances acted repulsiv.ely, and 

 he was at first ('84, p. 455) inclined to attribute this repulsion 

 to osmotic action, but later ('88, p. 624) he believed this view 

 disproved. The disproof he considered to lie in this, that 



