II THE PIGMENTS OF ORGANISMS 43 



Looking at the distribution of blue pigments 

 more in detail, we find that while blue and purple 

 colours are common in the Flowering Plants, there 

 is much uniformity in the pigments, which seem all 

 to belong to the anthocyan series. In the lower 

 plants blue pigments are more numerous. Thus 

 various blue and purple pigments have been described 

 among Bacteria — the blue or purple colour which 

 develops on decaying meat is a good example. 

 These pigments have been compared by some to 

 natural aniline dyes. With these, and as yet of little 

 interest except to the chemist, we may put the 

 bluish-green colours of certain Fungi. 



A more interesting pigment is phycocyan, which 

 occurs in the bluish-green Algse (Cyanophycese). It 

 is a beautiful pigment, blue in transmitted and blood- 

 red in reflected light, and is said by Molisch to be of 

 albuminoid nature. It is soluble in water, and has 

 been obtained in crystalline condition. 



In animals blue pigments seem to be more 

 numerous than in plants. They are found in various 

 Protozoa, as in Nassula and Stentor ; in the former 

 it seems possible that the pigment is taken up from 

 the blue-green Algae of the food. In the Coelentera 

 blue pigments are exceedingly common, especially 

 in shallow-water forms in warm seas, and in the 

 pelagic jelly-fish. In worms and in Echinoderms 

 we find that, although blue colours occur, the pig- 

 ments producing them do not appear to have been 

 isolated. Similarly in insects, where blue is very 

 common, blue pigments have not yet been described, 

 although it is improbable that the blue in all cases 

 is structural. 



