580 



have undertaken the investigation, whose chief results I have the 

 honour now to lay before the scientific world. 



The two genera Murex and Purpura have yielded the species 

 observed. In very distant localities, as at Mahon in Minorca, Murex 

 brandaris, M. trunculus, and Purpura hcemastoma have furnished 

 results which observations conducted at Boulogne on Purpura la- 

 pilluSy at Pornic (Vendee) on the same species and Murex erinaceus, 

 and at La Rochelle and L'lle de Rhe, have confirmed. At Marseilles, 

 Murex brandaris has yielded altogether similar results ; and this 

 concordance of all the observations permits me to offer them with 

 much confidence. 



What is the organ which produces the dye ? 



The analogy which some chemists imagine they have found 

 between the colour of alloxan or of murexide and the purple of the 

 Mollusca, has led them to misconceive the nature of the organ which 

 produces the colouring matter. It is indubitable that uric acid 

 treated with nitric acid gives a beautiful reddish purple colour when 

 the residue is exposed to ammoniacal vapour ; and this reaction 

 furnishes a means of detecting the renal organ in mollusks. But 

 from this circumstance no one could be justified in concluding that 

 the purple dye was either the secretion of the kidney or the result of 

 a modification of the urine. 



Careful dissection of the purpuriferous mollusca proves that the 

 purple dye is secreted by a very limited portion of the mantle, which 

 can in no way be confounded with the true renal organ, as which 

 the organ of Bojanus is now generally regarded ; the position and 

 the structure of the purpuriferous organ are indeed totally different 

 from those of the kidney. 



Small in extent, this part occupies very nearly the space bounded 

 by the branchiae and the rectum, beyond whose extremities it 

 hardly extends anteriorly, while posteriorly it, at most, reaches the 

 organ of Bojanus. It forms neither a sac nor a reservoir, as it has 

 been stated to do j and these phrases, as well as ' purpuriferous vein,' 

 should be rejected, because the organ is simply extended over the 

 surface. 



Large elongated cells, placed perpendicularly side by side on the 

 surface of the pallial cavity in the direction of its greatest diameter, 

 compose its tissue. They form about two or three layers, the most 



