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My dear Mr. Bell,—During the month of March, now past, and sincean abstract of mySecond Series of observations “On the Impregnation of the Ovum in the Amphibia” has appeared in the Proceedings of the Royal Society for June 1851, I have ascertained that the spermatozoa of the Frog are not only brought into contact with the surface of the egg, in fecundation, as already known, but that some of these bodies penetrate into the thick gelatinous envelopes, as stated by Prevost and Dumas: and further, I have found that in those eggs which are completely fecundated, some spermatozoa have arrived at, and become partially imbedded in the internal envelope which encloses the yelk, although I have not yet been able to detect any within the yelk itself; nor have obtained any evidence of the existence of an orifice, or natural perforation in the external envelopes, through which these bodies might enter.

Notes on the impregnation of the ovum in the amphibia: in a letter to Thomas Bell, Esq., Sec. R. S. Communicated by Mr. Bell