0)1 the Bones of the Sternum of young Tortoises. 319 XLII. — Additional Notes on the Form of the Bones in the 8ter7iuvi of very young Tortoises^ and their Development. By Dr, J. E. Gray, F.R.S. &c. [Plate XII.] The British Museum having received some young tortoises from North America, presented by the Smithsonian Institution, I have been induced to examine the form of the bones of the their sterna — and also the bones of the sterna of other young specimens that are in the Museum, some of which have been received since my former paper. As many of these specimens were in spirit before they were examined, it is necessary to observe that if the sternum is looked at as it is taken out of spirit, even when perfectly cleaned inside, it appears to be a uniform opaque disk, and the form of the bones cannot be observed even when held up to the light — until it is dried, when the cartilaginous part becomes transparent, showing the opaque bones ; and it becomes again opaque when again placed in proof spirit. I have had great difficulty in obtaining young specimens for the purpose of determining the development of the bones of the sternum, and have thought myself very fortunate when I have obtained one or two of a species ; and I thought that this arose from collectors thinking that young specimens would not be so much esteemed by Museum-directors as the others. But Prof. Agassiz, who lives and has collected in the country where tortoises are abundant, observes that the young Emydes live almost exclusively in water, much more so than their parents ; and though the young are naturally in much larger numbers than the adults, they are still so rarely found that they are almost unknown to zoologists. He observes : — " For example, Emys insculpta is so common in the neighbourhood of Lancaster that I have collected more than a hundred specimens in one afternoon, and yet I have never been able to obtain one of the first year, though a whole school of young men were called in to search. Prof. Baird has found the same difficulty in obtaining young Emys rugosa for me, and though he offered a high price for them he could not obtain more than a single specimen of the first year ; and yet this species is so common that, in the season, hundreds are daily brought to the market of Washington." ('Contribu-tions,' i. p. 294.) I have also been able to examine the sternum of the very young of two genera of land-tortoises that I had not before been able to examine and therefore to add them to my previous paper. 22*
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