406 PROF. TH. W. ENGBLMANN. 



by the nerves, as Lister ^ and Poucliet ^ have specially shown 

 with respect to the reflex of the eye. 



Differing, however, from the above-cited cases, we have the 

 behaviour of the protoplasm of Pelomyxa palustris.^ 



This large fresh- water Amceba creeps about very actively in 

 the dark, but when suddenly exposed to the light (diffused 

 daylight is sufficient) the streaming of the granules ceases, and 

 in a few seconds it draws itself together into a sphere. If it 

 continues exposed to the light, movements recommence, but of 

 a weak sluggish nature only. If the darkness is changed quite 

 gradually to light (the change extending over about a quarter 

 of an hour), there is no excitation-effect. There is also no 

 excitation-effect when, after long illumination, the light is 

 suddenly shut off. 



It should here be noted that when portions of green leaves 

 of Phanerogams, Mosses, or Fern prothalli are put into strong 

 shade and kept there for some time, they assume a darker 

 colouring in consequence of the gradual change of position of 

 the chlorophyll grains which are contained in the protoplasm. 

 These heap themselves together under the influence of 

 light — especially of short-wave rays — at the sides of the cells 

 which are turned towards the surface of the leaf, while in the 

 dark they accumulate at the walls of the cells perpendicular to 

 the surface. Although these changes certainly depend upon 

 the movement of the protoplasm, it must remain uncertain 

 how far they express a direct influence of light on protoplasm, 

 or an indirect influence in consequence of the primary changes 

 which the light exerts upon the chlorophyll bodies."* 



1 Jos. Lister, " On the Cutaneous Pigment System of the Frog," ' Phil. 

 Trans. Roy. Soc.,' cxlviii, p. 627, 1859. 



^ G. Pouchet, "Sur les rapides changements de coloration provoques 

 experimentalement chez les poissons," 'Compt. rend.,' Ixxxii, p. 866, 1871. 

 Cp. also G. Seidlitz, * Beitrage zur Desceudenztheorie,' Leipzig, 1876, who has 

 collected the instances of colour changes among animals. 



^ Th. W. Engelmann, " Ueber Reizung contr. Protopl. durch plotzliche 

 Beleuchtung," 'Arch. L d. ges. Physiol.,' xix, p. 1. 



■* Cp. J. Bohm, ' Sitzgsber. d. Wiener Acad.,' xxii, p. 476, 1856; xxxvii, 

 p. 475, 1859; xlvii, p. 352, 1863, A. Famintzin, 'Jahrb. f. wissensch. Bot.,' 



