430 Royal Society : — 



PROCEEDINGS OF LEARNED SOCIETIES. 



ROYAL SOCIETY. 



February 7, 1856. — Colonel Sabine, R.A., V.P. and Treasurer, in 



the Chair. 



" On the Vitahty of the Ova of the Salmonidse of different Ages ; 

 in a Letter addressed to Charles Darwin, Esq., M.A., V.P.R.S. &c." 

 By John Davy, M.D., F.R.S. Lond. and Edinb. &c. 



My dear Sir, — In a letter which I had the honour to address to 

 you last year " On the Ova of the Salmon in relation to the distri- 

 bution of Species," I have expressed the hope that some of the 

 results of observations therein described may aid in solving the 

 question as to the period, the age, at which the impregnated ova of 

 fish are most retentive of life, and consequently are in the state best 

 fitted for transport without loss of life. 



Joining with you in considering the subject in need of and deser- 

 ving further inquiry, I have taken the earliest opportunity that has 

 offered of resuming it. The experiments which I have made, and 

 which I shall now describe, have been more limited than I could 

 have wished, having been confined to the ova of the Charr, as I was 

 not able to obtain the ova of the Salmon or any of its congeners in a 

 fit state for the trials required. 



The ova of the Charr which have been the subject of my experi- 

 ments, were from living fish brought to me from the river Brathay, 

 a tributary of Windermere, on the 9th of November. They were ob- 

 tained by the pressure of the hand on the abdomen of the females 

 under water, and immediately after tlieir expulsion a portion of liquid 

 milt, procured in the same way from a male, was mixed with them 

 for the purpose of impregnation. 



The ova thus treated, 654 in number, procured from two fish, 

 were transferred, after little more than an hour, to a shallow glazed 

 earthenware pan, of a circular form, about a foot in diameter, vrith- 

 out gravel, the water in which, afterwards, was changed daily once, 

 and once only. The vessel was kept in a room of a temperature 

 fluctuating from about 55° Fahr. when highest, to about 40° when 

 lowest. The water used was well-water of considerable purity, and 

 before used it was allowed to acquire the temperature of the room. 



Two modes occurred to me as likely to afford the means of testing 

 the vital power of the ova, or their power of endurance without loss 

 of vitality ; viz. one by subjecting them for a limited time to a tem- 

 perature raised above the ordinary temperature ; the other, by having 

 them conveyed to a considerable distance. 



For the trials first proposed, the ova were put into a thin glass 

 vessel half-full of water, which was placed in a water-bath and heated 

 to the temperature desired. 



The first experiment was made on ova taken from the general stock 

 one day after their expulsion. Six, for two hours, were exposed to 

 a temperature varying from 79° to 80° of Fahr. The result was. 



