316 M. Rathke on the Development of the Chelonians. 



XXXV. — On the Development of the Chelonians. 

 ByH.lUTHKE*. 



I have for nine years been engaged in collecting materials for a 

 history of the development of the Chelonians, and I think of soon 

 publishing the result of my researches. I have had an oppor- 

 tunity of examining the embryo in a considerable number of 

 fresh eggs of Emys europcea, from its first appearance to the pe- 

 riod when the toes of the feet would soon have appeared. For 

 the knowledge of the succeeding periods of development, I had 

 at my disposal two almost mature embryos of Chelonia and Tes- 

 tudo and ten very young Chelonians of different species [Chelonia 

 My das, Sphargis coriacea, Trionyx gangeticus, Tr. ocellatus, Emys 

 europcea, Em. mauritanica, Cinosternum scorpioides, Cin. pensyl- 

 vanicum, Platemys Spixii, Pentonyx ....). 



The development of the embryos remains some time quite in 

 accordance with the general type of the development of the most 

 perfect vertebrated animal. It is especially the respective posi- 

 tion of the ventral and dorsal lamina? and of the spinal marrow 

 which does not differ in the least, either at the commencement 

 or at a later period, from what we observe in the higher verte- 

 brated animals. The remark of M. de Baer, u that, in the young 

 embryos of Emys europcea, the ventral lamina? are attached to the 

 dorsal laminae, at the point where the latter are united above to 

 close the dorsal furrow, and that the back itself is thus somewhat 

 depressed/' is a very pardonable error, as the embryo is at- 

 tached very strongly to the yolk, which is very tenacious in that 

 species. Nor can the assumption of my scientific friend be proved, 

 " that, in the Chelonians, the extremities are not detached from 

 the upper (or external) surface of the ventral and dorsal lamina?, 

 as in the other vertebrated animals, but from their lower (or in- 

 ternal) surface." I have found, on the contrary, in the youngest 

 embryos of Emys europcea, the extremities situated externally, in 

 the same parts of the body, and in the same manner as in the 

 embryos of the mammals, birds and Saurians. 



The embryos of Emys europcea, the extremities of which are so 

 developed that the digits must soon have appeared, but the ribs 

 of which were not yet visible, resemble excessively the very young 

 embryos of the Saurians and mammals. Their body in particular 

 is neither flattened above or below, nor too wide for its length, 

 and its dorsal part is insensibly continued (without interruption, 

 without elongated margin, as in the adult Chelonians) with the 

 neck, with the lateral parts and with the tail. Starting from the 

 examination of these young embryos and from the observations 



• Translated from the Annales des Sciences Naturelles for March 1846, 



