ON CERTAIN GREEN PIGMENTS IN INVERTEBRATES. 427 



on Scottish coasts^ is remarkable in having the epithelium 

 which covers the visceral hump coloured a bright vivid green, 

 which passes into brown at the margin of the mantle skirt. 

 Tlie epithelial layer which is turned in to cover the dorsal 

 surface of foot, is also coloured by the same pigment. The 

 pigment occurs as minute granules in the epithelial cells, and 

 in life varies from blue to green in colour. Sections of the 

 mantle skirt show that it is the superficial cells only which are 

 pigmented. At its margin the green pigment passes gradually 

 into a brown one of similar disti'ibution. The pigment of the 

 shell, it will be remembered, is deep brown. The green pig- 

 ment readily dissolves in sea water, in distilled water, or in 

 formalin. It is also soluble in alcohol, but is then apt to be 

 mingled with enterochlorophyll derived from the liver and gut. 

 When a number of limpets are preserved in formalin, the 

 formalin becomes clear greenish blue. The solution re- 

 sembles that of thalassemin in its colour, in turning distinctly 

 blue on the addition of acid, in being, at least in part, de- 

 colourised by alkalies, which tend to turn the pigment yellow. 

 The pigment also, of course, resembles thalassemin in its so- 

 lubility in water ; it differs from it in that I have not succeeded 

 in obtaining any band in its spectrum, and in that it is very un- 

 stable. In view of the effects of reagents on enterochlorophyll, 

 it does not seem to me improbable that this pigment is a 

 derivative of enterochlorophyll. There can be little doubt 

 that the brown pigment of the margin of the mantle is derived 

 from the green, and that it is identical with the pigment of the 

 shell ; this suggests the possibility that the enterochlorophyll 

 of the gut and liver, instead of being entirely eliminated with 

 the fseces, may give rise in the Mollusca to the bright pigments 

 of shell and mantle. There seems little doubt that soluble 

 green pigments, like those of Acmsea and Thalassema, are 

 widely distributed in Invertebrates ; whether they usually 

 originate in the way suggested here must, of course, remain at 

 present undetermined. Such a green pigment occurs, as I 

 believe, in many Annelids, notably in Eulalia viridis, 

 especially in the eggs, but is there not easy to extract. 



