ON CERTAIN GREEN PIGMENTS IN INVERTEBRATES. 425 



in addition a faint band in the green, probably corresponding 

 to the band in this position in acidified solutions. But a 

 similar band is represented in the normal solution of chaeto- 

 pterin, and apparently is absent in the alkaline solution only 

 because this is more dilute. The balance of evidence, therefore, 

 seems to me to be in favour of an affinity between the two 

 pigments. 



In their distribution, however, the two pigments seem to 

 differ markedly. Chsetopterin occurs in the Annelid Chseto- 

 pterus. " Enterochlorophyll," which is undoubtedly at least 

 nearly related, occurs in Mollusca and Echinoderma — not to 

 mention other doubtful cases. In these three sets of animals, 

 certainly not nearly related, the pigment when carefully 

 studied has been found to occur in eudodermal tissues, in 

 connection with the alimentary tract or its outgrowths. 

 There is, I believe, much evidence that bonellin is related to 

 chsetopterin and enterochlorophyll, and yet we find it described 

 as occurring in the epidermis and in " subepidermic cells 

 apparently belonging to the connective tissue,^^ — that is, in 

 ectodermal and mesodermal tissues. The latter position is 

 that also described for Professor Herdman^s (1) thalassemin — 

 a pigment differing markedly from bonellin. In view of these 

 facts tlie possibility suggests itself that in Bonellia a pigment 

 similar to chsetopterin occurs in the cells lining the gut; that, 

 instead of being eliminated intact with the fseces, as is entero- 

 chlorophyll in Patella, the pigment undergoes modification, 

 forming a green derivative which is deposited in granules in 

 the epidermis and underlying tissues. When Bonellia is 

 placed in alcohol both the original pigment and its derivative 

 may dissolve out, resulting in the formation of the solution 

 called alkaline bonellin. The suggestion seems to me to be 

 supported by a comparison with Professor Herdman's thalas- 

 semin. 



(2) Relation to Thalassemin. 

 The fact that although a green colour is common in the 

 Echiuridse, the peculiar pigment bonellin has only been 



VOL. 41, PAKT 3. NEW SKKIES. G G 



