1 8 OYSTERS AND DISEASE. 



all over the bodies of his oysters, kept in artificial tanks, and which culminated in 

 December in a more marked greening of the gills and labial palps, at the same time 

 that the oysters became thin, watery, and transparent. 



Our friend Dr. P. P. C. Hoek, of Helder, who happened to be working in our 

 laboratory soon afterwards, examined these green oysters with us ; and he has since 

 written to us about a diffused greenness (which we find to be the same as that from 

 Nieuport) which has broken out among the oysters stored on the farms at Bergen-op- 

 Zoom, on the East Scheldt. Dr. Bottemanne, Inspector of Fisheries at Zeeland, has 

 kindly sent us specimens of these green oysters from the Scheldt, and we find them to 

 be, like those sent from Nieuport by Dr. Pompe van Meerdervoort, very thin oysters, 

 in poor condition, with emaciated livers. Fig. 6 on PI. IV. shows one of the largest 

 of these Dutch oysters, and illustrates the characteristic colour of gill ; but in most 

 cases associated with this green colour we find a much smaller body, a shrunken liver, 

 .and a transparent watery mantle. Evidently mal-nutrition is one cause of the diffused 

 pale greenness of these Dutch oysters. The reason of the mal-nutrition in these localities 

 must be studied by some one on the spot ; but it very probably lies in the practice 

 of keeping the oysters in artificial cement tanks, into which water is only occasionally 

 admitted. Even although the sea-water contains the usual amount of food, still Diatoms 

 and other minute forms of life cannot be so abundant on the cement of the tank as 

 they are on the mud forming the bottoms of estuaries, " claires," and pits. 



Figs. 7 and 8 show, under a high power, sections of the external surface of the 

 mantle, where (Fig. 7) a certain amount of green pigmentation of the epithelial cells is 

 seen, in addition to several large coarsely-granular eosinophilous cells. There are also 

 (Fig. 8), in the connective tissue under the epithelium, groups of large green globules, 

 which are evidently MacMunn's " entero-chlorophyll." Fig. 10, showing a transverse 

 section of the intestine unstained, is of considerable interest, as it shows that the green 

 colour of the alimentary tract of this variety is due to a pigment in the epithelial cells. 

 Thus the green colouration of this oyster is not similar to that found in the American 

 oysters. Nor do we consider that it is identical with the green of the Marennes oyster, 

 as the pigment is here (as our figures show) more generally diffused through the 

 epithelium, and not aggregated in " macroblasts." The distribution and general appear- 

 ance of these minute pigment granules recalls that of the green granules in the 

 intestinal epithelium of Chcstopterus, as described and figured by Ray Lankester ; * but 

 the two pigments are quite distinct in their nature. It is evident, from recent work by 

 Professor Lankester, Miss Newbigin, and others, that entirely distinct animal pigments 

 may seem histologically very much alike in position and appearance.! 



4. Falmouth Green Oysters. — From time to time in the past, since 17 13, when 

 a case of poisoning at the HagueJ was attributed to oysters unlawfully coloured with 



* Quart. Jour. Micros. Sci., vol. XL., p. 447. 



\ See Miss Newbigin's recent Paper in Quart. Jour. Micros. Sci., Nov. 1898. 



XSee O'Shaughnessy— Ann. and Mag. Nat. Hist., vol. XVIII., 1866. 



