610 SCIENTIFIC RECORD FOR 1884. 



casts suspiciou ou the value of the former. There are likewise many 

 other failures thau those mentioned of constituents of groups to embody; 

 the requisites of the diagnoses of such groups. On the whole, then, we 

 cannot concede that the new arrangement is Superior to those that have 

 preceded. It is, nevertheless, of some value as an incentive to further 

 study of the subject, in order to test the value of various propositions. 



The Eyes of Bivalve Mollnslis. — If the edges of the mantle of even our 

 common bivalve moUusks, such as the oyster, the hard clam, and the 

 soft clam, are very closely examined, specks may be found which prove 

 to be rudimentary eyes. These organs have been recently examined by 

 Dr. Benjamin Sharp, of Philadelphia, who has studied them in the 

 oyster, the hard clam, the soft clam, the common mussel {Mytilus edulis), 

 the big clam [Mactra solidissima), and two razor-fishes [Solen ensis and 

 Solen vagina). The pigmented cells found in these parts are essentially 

 the same in all. The smallest of the cells were found in the oyster, and 

 the largest in the hard clam. Experiments on these forms show their 

 sensitiveness to light and shadow, and the cells showing the retinal 

 character described leaves little doubt as to the power of vision. No 

 nerves could be demonstrated passing direct to these cells, and proba- 

 bly those distributed to the general epidermis serve in transmitting thii 

 impressions. The visual power is so low that nerves have not yet been 

 specialized for this purpose." {Proc. Acad. Nat. iSc. Phila., 1884, p. 10). 



The Greening of Oysters and its Cause.— There is always a reason or the 

 appearance of a reason for a given phenomenon engendered by popular 

 opinion, and one was devised to explain the cause of the green color so 

 prevalent in the British oysters especially. The reasoning in this case 

 was very facile. 



Oysters are green; copper in oxidization becomes green. Therefore 

 the green color of oysters is due to the absorption of copper; conse- 

 qeutly the bottom of the sea, or the sea itself, is pregnant with copper. 

 The oysters have a " coppery taste," and thus give proof of the exist- 

 ence of copper. 



Science doubted and suggested explanations, but not until lately has 

 the question been approached in a severe critical and experimental man- 

 ner. An old suggestion was then proved to be practically correct. The 

 most recent and skilled of the inquirers into the cause and origin of the 

 greening of the oysters are Mr. Puys6gur, an assistant commissioner of 

 the navy department of France, and Mr. John A. Ryder, of the United 

 States Commission of Fish and Fisheries. 



Mr. Puysegur has recalled the history of conjecture and research on 

 the cause of the green color of oysters and given the results of his own 

 investigations. 



He tested the popular view that the color was the result of suffusion 

 with copper. Even a meritorious chemist, Mr. Gaillard, had found cop- 



