412 MARION I. NEWBIGIN. 



(2) Mode of Occurrence. 



Dr. MacMunn describes enterochlorophyll in various Echi- 

 noderms as well as in the Mollusca; my own observations 

 were made entirely on the Mollusca. As the pigment occurs 

 in relatively small amount, it is necessary to choose a form 

 which can be obtained in large quantity. The garden snail 

 (Helix aspersa) and the common limpet (Patella vulgata) 

 both fulfil this condition^ but I soon found that the snail 

 contains a very much smaller amount of pigment than the 

 limpet, and in consequence^ in spite of the greater difficulty 

 in dissection, the latter was employed in all the later observa- 

 tions. 



In the limpet the pigment has been described by Dr. Mac- 

 Munn in the '' liver" and in its secretion; I find it also in the 

 cells of the gut, in the contents of the gut, and in very pure 

 condition in the fseces. In all these situations it can be re- 

 cognised by the microchemical reaction already described for 

 chsetopterin (p. 393) — the vivid green colour with hydrochloric 

 acid. 



In order to study the distribution of the pigment in the 

 "liver" and intestine, portions of the visceral hump were 

 hardened in formalin, and sections cut through both the 

 digestive gland and the coils of the intestine. The sections of 

 the gut show with low power a band of brownish-green pig- 

 ment placed in the epithelial cells near their inner margin 

 (see fig. 9). When examined under a higher power (fig. 10) 

 the pigment is seen to occur in minute closely packed granules, 

 brownish green in mass, green when viewed singly. They in 

 all respects resemble the granules in the cells of the gut in 

 Chsetopterus, but the amount of pigment is much smaller. 

 The sections of the tubules of the digestive gland (fig. 11) do 

 not show cells having this peculiar granular appearance. The 

 large cells near their inner surface contain several of the 

 characteristic raoUuscan pigmented vesicles, usually of a 

 brownish-yellow colour, while scattered through the proto- 



