Letter, 'On the vitality of the ova of the Salmonidae of different ages' from John Davy to Charles Darwin Davy expresses his aim to identify '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'. He communicates details of his experiments and research into this matter. He concludes from his experimental results that 'the strength of vitality of the impregnated ovum, or its power of resisting agencies unfavourable to its life, gradually increases with age and the process of foetal development'. Subject: Biology / Zoology / Reproduction Received 15 January 1856. Read 7 February 1856. Written by Davy at Lesketh How, Ambleside [England]. This letter was published in full in volume 8 of the Proceedings of the Royal Society as 'On the vitality of the ova of the salmonidæ of different ages; in a letter addressed to Charles Darwin, Esq., M. A., V. P. R. S. &c'. 10 January 1856