On the suggestion of Jeffries Wyman, he writes about the rats that he captured in Mammoth Cave in 1850. They were indeed blind. Reginald Mantell studied them and learned that with long exposure to graduated light, they became somewhat sensitised. Sends copy of an abstract which he wrote as a letter to A. H. Guyot ["On the Mammoth Cave of Kentucky", Am. Journal of Sci. and Arts 2d ser. 11 (1851)]. [See 3007.]