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XXXII. — On the Urinary Secretion of Fishes, with some Remarks on this Secre* 

 tion in other Classes of Animals. By John Davy, M.D., F.R.SS, Loiid. and 

 Edin., &c. 



(Read 2d February 1857.) 



Notwithstanding the progress made of late years in animal chemistry in con- 

 nection with comparative anatomy, I am not aware of any observations that have 

 yet been published on the urinary secretion of fishes. The neglect of this inquiry 

 probably has arisen from several circumstances, — the nature of the element in- 

 habited, the peculiarities of the urinary organs, the difficulty of collecting the 

 matter voided, and its having no well-marked distinctive qualities obvious to the 

 senses. 



For some years, as leisure and opportunities offered, I have given attention 

 to the subject, and in the paper which now I have the honour to submit to the 

 Society, I beg to communicate the observations I have made. Few and im- 

 perfect as these are, they are given mainly with the hope of attracting notice to 

 the inquiry and of inducing others more favourably situated to engage in its 

 prosecution. 



The fishes I have examined in search of their urinary secretion have been the 

 following, — the salmon, sea-trout, charr, common trout, pike, and perch ; the 

 skate, ling, conger, cod, pollack, haddock, turbot, bream, and mackerel. 



Of these the salmonidse, pike, perch, ling, and ray, have a small urinary blad- 

 der ; and in all but the last communicating directly with the kidneys. In the 

 last mentioned, the ray, the communication appears to be indirect, after the 

 manner observable in some of the batrachians, in which the ureters terminate in 

 the cloaca. 



The other fishes named seem to be destitute of a urinary bladder, or, if pos- 

 sessed of one, it was so small as to have escaped observation. The ureter in 

 these, when distinct, was found to terminate near the verge of the anal aperture ; 

 in several instances it was so large and dilated as to serve the place of a bladder. 



In the small urinary bladder of the salmonidse (so small as to be little more 

 than rudimentary), I have never found any fluid collected. In the bladder of a 

 trout (Salmo fario) taken in June, in Windermere, when in highest condition, 

 there was seen a little whitish mucus-like matter. Tested by nitric acid and heat 

 properly graduated, it became yellow, without the slightest purplish tinge, indi- 

 cative of the presence of lithic acid. 



The urinary bladder of the perch {Perca fluviatilis) is larger, and internally pli- 

 cated and spongy, and has been found to contain a fluid. In that of one, — a fishy 



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