Sensory reactions of Holothuria surinamensis. 275 



made with distilled water, alcohol, and formalin. Their properties 

 were practically identical with those of the materials obtained b}»" 

 MacMunn (1889) from the integument of H. {nigra) forslioli and ^wZ« 

 (cf. also Dubois, 1906).^) The coloring matter is largely confined 

 to the superficial layer of the integument, from which it was very 

 easily dissolved. The solutions were yellow by transmitted light, 

 and exhibited a pronounced blue-green fluorescence very similar to 

 that of nranium-glass. The pigment of H. captiva was much darker 

 than that of surinamensis. Solutions in alcohol, formalin, or acetone 

 gave identical absorption spectra, showing no bands, but a general 

 absorption in the green-blue, which was greater in the case of 

 H. captiva; MacMunn (1889) found absorption bands only with ex- 

 tracts from H. poli. The pigment was not affected by acids -) 

 (hydrochloric, sulphuric, nitric, formic, acetic), but an excess of 

 sodium or potassium hydroxide caused complete precipitation in the 

 form of a light green-brown collodial mass, which dried in black 

 flakes.'^) The coloring matter is chemically changed in the presence 

 of hydroxides, as the well washed precipitates were only very 

 slightly soluble in distilled water. They were likewise insoluble 

 in ether, chloroform, carbon tetrachloride, benzene, or carbon bisul- 

 phide, and only partially soluble in xylol. A slight excess of hydro- 

 chloric or acetic acid redissolved the precipitate, and such re-solu- 

 tions had the absorption spectrum and other properties of the 

 original extracts. The green color was not removed by boiling 

 (tho fluoresence was greatly reduced thereby), nor by treatment 

 with hydrogen peroxide. When alcoholic solutions were exposed to 

 the light and air for several weeks, they gradually became colorless, 

 while control solutions in stoppered flasks retained their original hue. 

 2) The fluorescent pigment of Holothuria has been described at 

 length, because I believe that either the pigment is itself the essen- 

 tial photo-sensitive material, or else that it acts as a sensitizer for 

 the true photo-receptor. It is assumed that there is present in the 

 integumentary cells of Holothuria a substance that is chemically 



1) According to Beiot (1906) the yellow-brown pigment of H. tubulosa 

 is not fluorescent. 



2) The prolonged action of nitric acid weakens the color, first 

 destroying the fluoresence. 



3) The continued action of concentrated sodium hydroxide destroyed 

 the green color after several days ; the residue was soluble in acids, but 

 these solutions were colorless. 



