304 SKIN PIGMENTS OF NUDIBRANCHS 



Solutions of the blue material were compared in the case of the 

 three species: Chromodoris zebra from Bermuda, Chromodoris por- 

 iercE from La Jolla, California, and Chromodoris universitatis from 

 Laguna Beach, California. An extract from specimens of any of 

 these species in aqueous formaldehyde, is bluish purple in color, turned 

 pink by acids at about pH 5.6, and changed to blue (with some pre- 

 cipitation of a greenish flocculent material) by alkali.^ In some other 

 qualitative respects the substances extracted from the three species 

 also agree, notably in yielding positive tests for the presence of manga- 

 nese, and in being decolorized, reversibly reduced, by putrefactive 

 bacteria; but the most important data are derived from the absorption 

 spectra. In formaldehyde solution the Chromodoris zebra pigment 

 gives a narrow, sharply bounded absorption band centering on 620 to 

 6TI1XH. In alcoholic extract, neutral or faintly acid, the absorption 

 band likewise centers at 622/i/i. 



The extracts are stable for at least several years (especially if 

 shielded from bright sunlight), hence it is unnecessary to employ 

 freshly prepared solutions of the pigments. Chromodoris porter ce pig- 

 ment, in the comparison spectroscope, gave an absorption which could 

 not be distinguished from that of Chromodoris zebra, and, as deter- 

 mined by successive dilutions, the absorption maximum was also at 

 about 620/iAi. This is likewise true of the pigment of Chromodoris 

 universitatis. 



It is believed, consequently, that the blue pigment which has a 

 special importance for the coloration of the genus Chromodoris is a 

 very similar body, chemically, in widely dispersed species of this 

 genus ;^ and since the habits of the various species differ considerably, 

 it must be reckoned as a distinct probability, therefore, that the pig- 

 ment has primarily no relation to the habits of these animals, but is 

 an expression, merely, of the fundamental chemistry of the Chro- 

 modorid stock. 



^ cf. Crozier, W. J., 1916, /. Biol. Chem., xxiv, 255. In alcoholic solution the 

 green material is soluble. 



^ Chromodoris portercB were obtained from the Scripps Institution, and Chro- 

 modoris portercB and Chromodoris universitatis from Professor W. A. Hilton of 

 Pomona College; the author is grateful for this assistance. 



