PROTOPLASMIC MOVEMENT. 405 



corpuscles and other amcfiboicl cells of Vertebrata and 

 Invertebrata,^ the common Amoebae, many Rhizopods, In- 

 fusoria, and vegetable cells. ^ In green cells from which 

 light is shut off, the movement stops, but only with the 

 whole vegetation of the plant ; in Char a, for instance, 

 as shown by Dutrochet,^ only after twenty-four to twenty- 

 six days. 



In special cases the intimate structure of the protoplasm 

 obviously alters with long exposure to light or the reverse. 

 The Plasmodium of vEthalium creeping upon the surface of 

 tan while in the dark will withdraw itself again into the deeper 

 layers upon exposure to bright light, and while in the light it 

 puts forth only short much crowded processes, in the dark 

 long, narrow, thin branches are developed.* Here then 

 illumination appears to act similarly to artificial stimuli. It 

 is also well known that changes in the illumination cause 

 changes in the contractile pigment cells which occur in 

 the skin of many Fishes, Amphibia, and Reptiles — changes 

 which bring about a change in the colour of the whole 

 animal. The black pigment cells, for instance, in the frog's 

 cutis, which in the dark are much branched, contract 

 gradually upon exposure to a bright light to small spheres, 

 in consequence of which the skin appears lighter in colour. 

 But it appears that in this case the action of the light 

 upon the contractile elements is indirect, and is transmitted 



' Author's and other observations. 



- Cp. Jul. Sachs, " Ueber den Einfluss des Tageslichtes, &c.," * Botan. 

 Ztg.,' 1S63. W. Hofmeister, 'Die Lehre von der Pflanzeuzelle,' p. 49, 

 1S67. G. Kraus, " Ueber Versuche mit Pflauzeu in farbigem Lichte," 

 ' Sitsungsber. d. naturf. Gesellsch.,' Halle, v, 20 May, 1876 ; ' Botan. Ztg.,' 

 1876, p. 504 (yellow light is without influence upon Hydrocharis, 

 Triauea, Chara, Vallisneria, Elodea, Pilobolus, Urtica dioica, 

 Navicula). 



3 Dutrochet, ' Compt. rend.,' ii, p. 779, 1837. 



■* Hofmeister, 'Die Lehre von der Pflanzenzelle,' p. 21, 1867; Baranetsky, 

 " Influence de la lumiere sur les plasmodia des Myxomycetes," 'Mem. Soc. 

 des Sciences Nat. Cherbourg,' xix, p. 321, 1875 (finds the blue rays specially 

 active, the yellow not). 



