1 84 HOLMES. [VOL. II. 



The pigment spots of Amphithoe apparently contain but 

 one kind of pigment. The whole system of chromatophores is 

 much less complicated than that which Gamble and Keeble : 

 found in Hippolyte varians, and the power of sympathetic color 

 changes in relation to surrounding objects much less perfectly 

 developed. Amphithoe may be said to adapt its color to its 

 environment, but in only a rather rough way compared with the 

 remarkable protective color changes of Hippolyte. Specimens 

 taken from the eel-grass are very apt to be of a greenish color, 

 and specimens taken from among masses of red seaweed are 

 usually colored somewhat like their environment. While on 

 the eel-grass, they are usually exposed to the light and the pig- 

 ment spots are in a contracted condition. This allows the green 

 color of the tissues to be seen, and the animal has, consequently, 

 a greenish aspect. In the masses of red seaweed the animal 

 is usually more shaded and the pigment spots become expanded, 

 giving the animal a reddish tint which helps to conceal it in its 

 environment. Moreover the alimentary canal in specimens 

 found in the red seaweed often contains a greater or less 

 quantity of this alga, and this also helps to color the animal in 

 a protective manner. So far as the green color of the tissues 

 is concerned there appears to be no difference between the 

 animals from different habitats. The change from green to 

 reddish, or the reverse, completes the range of adaptive color 

 variations in this species so far as they are induced by changes 

 in the environment. And this kind of color change is the 

 one best adapted to afford protection to the species in its usual 

 habitat. 



The pigment spots of Amphithoe change very slowly ; it 

 generally requires some hours to effect a change from the 

 expanded to the contracted condition. It was found by several 

 experiments that exposure to bright light causes the pigment 

 spots to contract, while specimens that have been kept in the 

 dark for several hours generally have the pigment spots much 

 expanded. 



1 Quart. Journ. ilficr. -SV/., 1900. 



