VI COLOURS OF CRUSTACEA AND ECHINODERMA 125 



the Challenger remarked on the fact that a bright 

 red pigment (which he called crustaceorubrin) should 

 occur in small surface forms like Daphnia, and 

 then reappear in the ocean depths. The probability 

 is, however, that this pigment is very widely dis- 

 tributed in the Crustacea, and that its apparent colour 

 depends upon the conditions under which it occurs. 



As to the simultaneous occurrence of red and 

 yellow lipochromes in the Crustacea, there is no 

 doubt that by various agents, and especially in the 

 presence of heat, both red and yellow pigments can 

 be extracted from the skin and shell of the lobster 

 and crayfish. I am, however, much inclined to doubt 

 the existence of both these pigments in the living 

 condition. Certainly the yellow, if it exists, has 

 practically no effect upon the coloration. The epi- 

 dermis of the lobster yields to water a beautiful 

 bright red solution, with no trace of orange, and does 

 not on filtering leave behind any orange or yellow 

 pigment. Lipochromes as such are of course not 

 soluble in water, but the red ones dissolve very 

 readily in solutions containing albumen. 



The red lipochromes, when in solution in water 

 containing proteid, are precipitated with the proteid 

 on boiling, but if alkali be added to the solution, 

 alkali-albumen is formed, and they are not precipitated 

 even on boiling. The fact that the red lipochromes 

 thus form compounds with alkalies which are soluble 

 in albuminous solutions, is one of considerable in- 

 terest to which we shall recur. 



2. The Soluble Blue Pigments. — These unstable 

 pigments constitute the cyanic series of Pouchet, 

 the lipochromogens of Krukenberg. They occur 



