CiiAr. III. YOUNG TURTLES. 389 



There is an early period in the development of the Testudinata,^ when the 

 embryo presents the most striking resemblance to that of any other allantoidian 

 Vertebrate. At that age the embryo has not the remotest resemblance to a Tur- 

 tle. It is then slender, and comparatively much longer than wide. (PI. 6, fig. 

 28-32; PL 13, fig. 2-9; PI. 14, fig. 2a, and 3-9; PI. IG, fig. 6; and PI. 18a, fig. 

 2 and 14.) There is no sign of the characteristic shield ; the whole body is as 

 elongated as that of a young snake of a corresponding age;^ the head is very 

 large in comparison with the size of the animal ; the eyes, especially, are large and 

 prominent (PI. 14, fig. 3); the trunk is broader forward, and tapers gradually back- 

 ward to a long tail ; the limbs, when first formed, project only as small rounded 

 paddles. (PI. 6, fig. 28-32.) 



AVhen the shield makes its first appearance, it is only a fold in the skin, 

 extending on both sides of the main axis, and converging in front of the Ijody 

 and over the tail. (Sec PL 15, fig. 13; and PL 6, fig. 2G and 27.) The body 

 being still very long, the outline of this fold, when seen from above, has an ovate 

 form. The tail of the Caouana, so short afterwards, is still as long as in the 

 Amydas, and its feet not longer than those of the Amydos. (See PL 6, fig. 24-27.) 

 At this age all Turtles resemble one another. I have seen Chelonioida>, Chelj^droidte, 

 Trionychidas, Cinosternoidtc, and a number of species of Em^doidie in this condi- 

 tion of development, which could not be distinguished one from the other. 



Gradually the sides widen, so that the preponderance of the longitudinal over 

 the transverse diameter is considerably lessened, and the characteristic features of 

 the Turtles are brought out distinctly. (See PL 6, fig. 10-12, fig. 22-25; PL 9c, 

 fig. 9-12, 18, 19, and 22, 23; PL 14, fig. 1; PL 15, fig. 4-6; PL 16, fig. 5; and PL 

 18a, fig. 2. See also Rathke, Entw. der Schildkroten, PL 10, fig. 8 and 9.) At 

 this stage of the development the young of all the Testudinata have still the same 

 form, to whatever family they may belong ; but, as far as a dorsal shield is char- 

 acteristic of Turtles, they are unmistakable Turtles. That no femily diflerence can 

 as yet be perceived is plain from the foct, that the figures here referred to 

 represent the young of Clielonioidje, of Chelydroid*, of Cinosternoida^, and of Emy- 

 doidre.^ The most remarkable features of this age consist not only in the perfect 

 identity of the fonn, of the limbs, and of the shield, but also in the greater width 

 of the anterior part of the shield, and in the great preponderance of the head. 



But now great changes take place. Henceforth the 3'oung of different fami- 



^ The earliest st.iges of development are de- ' PI. G, fig. 22-25, represent the embryo of Tha- 



scriljcd ill Part III. with t'ullcr comparisons witii the lassochelys Caouana; PI. <>, fig. 10-12, that of Ozo- 



other allnntuidian Vertebrates. theca odorata; PI. 9c, fig. 9-12, that of Chelvdra ser- 



- Compare Rathke, Entwickcduiigsgescli. d. Niit- pentina ; and PI. 9c, fig. 18, 19, and 22, 23, liiat of 



ter, PI. 1, fig. 3 and 4, with my fig. 1, Pi. 14. Chrysemys pieta. 



