738 NATURAL HISTORY OF AQUATIC ANIMALS. 



putrefactive changes, one which I find almost uniformly present is a filiform or thread-like organ- 

 ism allied to Spirillum. It, however, was always found in the stomach in great abundance, and 

 especially in the pyloric portion of the intestine in which the crystalline style is lodged. This 

 organism is probably harmless; a similar one is frequently found in both fresh and salt water, 

 and has at times been developed in prodigious numbers in the reservoirs from which the supplies 

 of water were drawn for a large city, without any evidence of its having produced a harmful 

 effect upon those who drank of the water. 



VIEWS OF LEIDY, PUYSEGUR, AND DECAISNE. Professor Leidy, at a recent meeting of 

 the Academy of Natural Sciences of Philadelphia, stated it as his belief that Oysters feed at 

 times on the zoospores of certain algae, as those of Ulna latissima (sea cabbage), 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 as sometimes observed in certain localities. 

 Very possibly this may be the case, but judging from what I have seen and heard from oyster- 

 men, as well as from what I have read in various publications relating to this matter, I am not 

 inclined to regard this as the only source of the unusual green tint of the flesh of the Oyster. 

 I hope to be able to show that it is probably of vegetable origin, and therefore quite harmless. 

 That it is not copper we may be equally certain, as Professor Lewis' tests have shown, for 

 any such quantity of a copper salt as would produce the green gills, heart, and cysts in 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 Decaisne, who found that when perfectly white-fleshed Oysters 

 were supplied 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 imbued with this vegetable green 

 were placed in sea- water deprived of the microscopic vegetable food the characteristic color would 

 also disappear. Whether this will finally be found to be the explanation in all cases remains to 

 be seen, as some recent investigations appear to indicate that it is possible that a green coloration 

 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. 



GEDDES UPON CHLOBOPHYL-CONTAINING ANIMALS. 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, etc.); secondly, those vegetating by their own 

 intrinsic chlorophyl (Convoluta, Spongilla, Hydra); thirdly, those vegetating by proxy, if one may 

 so speak, rearing copious algae in their own tissues, and profiting in every way by the vital 

 activities of these." This latter is one of the most interesting and important of modern biological 

 discoveries, that living animal bodies may actually afford a nidus for the propagation of green 

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

 off by the parasitic vegetable organism appears to be absorbed by the tissues of the animal host, 

 while the carbonic acid gas thrown off by the latter is absorbed by the vegetable parasite, thus 

 affording each other mutual help in the processes of nutrition and excretion. This singular 

 association and interdependence of the animal host and vegetable guest has received the some- 

 what cumbrous name of Symbiosis, which may be translated pretty nearly by the phrase "asso- 

 ciated existence." This is not the place for the discussion of the purely scientific aspect of this 

 question as already ably dealt with by Dr. Brandt, Patrick Geddes, Geza Entz, and others, and 



