PHYSIOLOGY OF THE INVERTEBRATA. 285 



After dissecting the nephridia from the bodies of a large 

 number of fresh limpets, the secretions of the left nephridia 

 were examined separately from those of the right nephridia. 



Both secretions were examined chemically by two separate 

 methods as follows : 



(a) The clear liquid from the nephridia was treated with a 

 hot dilute solution of sodium hydroxide. On the addition of 

 HOI a slight flaky precipitate was obtained after standing 

 for some time. These flakes when examined microscopically 

 were seen to consist of small rhombic plates and other 

 forms. On treating the secretion alone with alcohol, 

 rhombic crystals were deposited, which were soluble in 

 water. When these crystals were treated with nitric acid 

 and then gently heated with ammonia, reddish-purple 

 murexide was obtained. 



(6) The second method for testing the secretion of the 

 nephridia of Patella was as follows : The secretion was boiled 

 in distilled water, and then evaporated carefully to dryness. 

 The residue so obtained was treated with absolute alcohol 

 and filtered. Boiling water was poured upon the residue, 

 and to the aqueous filtrate an excess of pure acetic acid was 

 added. After standing about seven hours, crystals of uric 

 acid (OjH^NiOa) were deposited, and readily recognised by 

 the chemico-microscopical tests mentioned above. 



The secretions of both the left and right nephridia yield 

 uric acid. It has been suggested by Professor E. J. Harvey 

 Gibson (in his masterly memoir on the " Anatomy and Phy- 

 siology of Patella imlgata"*) that the secretions of the two 

 nephridia may be chemically distinct. The author could not 

 extract or detect (after a most searching investigation) the 

 presence of any other substance besides uric acid in the 

 secretion of either nephridium. The isolation of uric acid 

 proves the renal function of the nephridia of Patella md- 

 gata. 



The nephridia of the Cephalopoda have also been examined 

 * Transactions of Boyal Society of Edinhurgh, vol. 32, p. 601. 



