410 BULLLEIN OF THE UNITED STATES FISH COMMISSION. 



first apxiear, many of them donbtless have some foundation in substan- 

 tial fact. 



Professor Leidy, before the Academy of Natural Sciences of Philadel- 

 phia, has recently stated it as his belief that oysters probably feed on 

 the zoospores of certain algte, such as those of JJlva latissima (sea cab- 

 bage), which he knew from personal observation to be green, and which 

 he thought might possibly be the cause of the green coloration of the 

 soft parts of the animal frequently observed in both the American and 

 European species, and which, I am convinced from observation, origi- 

 nates from the same source in both species. Yery possibly the spores 

 of UJva may be the cause, but, judging from what I have seen and 

 heard from oystermen, as well as from what I have read in various pub- 

 lications relating to this matter, I am not inclined to regard this as the 

 only source of the green observed in the oyster. Without being able to 

 state positively what it is, we may take it for granted that the color 

 is of vegetable origin, and therefore quite harmless. That it is not 

 copper we may be equally certain, for any such quantity of a copj)er 

 salt as would produce the green gills and patches on the mantle, such 

 as are often observed, would without doubt be as fatally poisonous to 

 the oyster as to a human being. The source of the green has recently 

 been investigated by two French savants, MM. Puysegur and De. 

 caisue, whp found that when perfectly white-fleshed oysters were sup- 

 plied with water containing an abundance of a green microscopic plant, 

 the Navicula ostrearia of Kiitzing, their flesh acquired a corresponding 

 green tint. These investigators also found that if the oysters which 

 they had caused to become impregnated with this vegetable color were 

 placed in sea- water deprived of the microscopic green vegetable food, 

 the characteristic color would also disappear. Whether this will fin- 

 ally be found to be the true explanation remains to be seen, as some 

 recent investigations indicate that it is possible that a green colora- 

 tion of animal organisms may be due to one of three other causes besides 

 the one described above as the source of the green color of the oyster. 

 Patrick Geddes, in a recent number of Nature, has pointed out that 

 "the list of supposed chlorophyl containing animals * * * breaks up 

 into three categories : first, those which do not contain chlorophyl at all, 

 but green pigments of unknown function {Bonellia, Idotea, d;c.) ; secondly, 

 those vegetating by their own intrinsic chlorophyl {Convohita, SpongiUay 

 Hydra)', thirdly, those vegetating by proxy, if one may so speak, rear- 

 ing copious algje in their own tissues, and profiting in every way by 

 the vital activities of these." The last is one of the most interesting and 

 important of modern biological discoveries, that living animal bodies 

 may actually attbrd a nidus for the propagation of green microscopic 

 plants, and not be injured but rather be benefited thereby. The oxygen 

 thrown oti" by the parasitic vegetable life appears to be absorbed by the 

 tissues of the animal, while the carbonic dioxide gas thrown off" by the 

 latter is absorbed by the vegetable parasite, thus affording each other 



