228 BULLETIN OF THE BUREAU OF FISHERIES. 



In such cases the problem of color is transferred from the animal to the plant, which 

 relieves the present discussion of any particular consideration of the matter. It may 

 suffice, therefore, to say that in such cases color is only of secondary or incidental bio- 

 logical significance, and is meaningless in relation to any problem of adaptation or 

 protection. In the words of Duerden, "The rich profusion and beauty of color in 

 coral polyps certainly seems to have no protective or warning significance" (op. cit., 

 p. 16). 



But even in organisms in which color is constitutional there is little or no relation 

 to environmental influences. For example, many actinians aud alcyonarians living 

 under identical conditions have very different color features; and, on the other hand, 

 species of widely differing habitats and diverse environments exhibit closely similar 

 aspects of coloration. Furthermore, a species which shows remarkable color variations 

 in a given habitat will often show the same variations through its entire range of dis- 

 tribution. As an example of this may be cited the well-known case of the common 

 Metridium maroinatum. The world-wide distribution of this species (assuming with 

 McMurrich its identity with M. dianthus), and the very similar aspects of coloration, 

 illustrates the point under consideration, showing that conditions of environment or 

 habitat have little to do with the character or variation of colors, at least so far as this 

 species may have any significance. 



The influence of conditions of nutrition, as already shown by me in former papers 

 (op. cit.), act in similar manner on Anthozoa. Actinians kept in the aquarium very 

 soon show color changes indicative of lowered states of vitality, unless pains be taken 

 to obtain approximately natural conditions. In the celebrated Naples aquarium this 

 has been more successfully done than I have seen elsewhere. Here certain species of 

 actinians have thrived for years with little loss of vitality or change of coloration. 



PHOSPHORESCENCE. 



Among the many various and complex phenomena of life few are more unique or 

 obscure than that of phosphorescence, or vital luminosity, the former name being more 

 or less a misnomer, since except in appearance there is little or nothing in common 

 between the phenomena to which it was originally applied, and those associated with 

 living things. However, the term has become so generally associated with all sorts of 

 luminous phenomena of similar appearance, and devoid of appreciable heat, that its 

 use is likely to continue; and if care be taken to discriminate no serious confusion is 

 likely to arise. 



The occurrence of phosphorescence in many species, and in a wide range throughout 

 the entire class, makes some reference to the subject more or less incumbent. While 

 probably much more general in tropical and subtropical waters it is yet fairly common 

 elsewhere, being well known throughout the region concerned in this report. 



Much speculation has been aroused concerning its use or significance, and various 

 and conflicting theories projected. No attempt will be made here to review the subject 

 historically, nor to cite the various differences of opinion which have grown up. 



