390 



AMERICAN TESTUDIXATA. 



Part II. 



lies present marked diflferences. The Chelonioidce become Chelonioid ; the Chely- 

 droidtB, Chelydroid; the Cinosternoidas, Cinosternoid : the Emydoidre, however, assume 

 specific ciiaracters before they take on their Emydoid form. Though the Chelo- 

 nioida) do not widen as much in proportion to their length as the representatives 

 of other families, the increase in width, as far as it extends in them, takes place 

 chiefly in the anterior part of the shield, so that their form becomes more heart- 

 shaped (PL 6, fig. 18-21); or, what is the same, leans already towards the form of 

 the adult.^ The presence of large epidermal scales upon the shield shows already, 

 at this early age, that this young sea Turtle must belong to the family of Che- 

 lonioida?, and not to that of SphargididiB. In CinosternoidEe, Chelydroidre, and Emy- 

 doidae the shield widens more in the posterior part; especially in Cinosternoidae, 

 which remain narrow (PI. 9c, fig. 8) for a longer time than either Chelydroidae and 

 Emydoida?, — or, what is the same, the CinosternoidiB assume earlier than either the 

 Chelydroidaj or Emydoidce a tendency towards their permanent form. The Cinos- 

 ternoidae and the Chelydroidae are, moreover, impressed with other characters peculiar 

 to their family at an earlier period than the Emydoidae. Thus the peculiar sculp- 

 ture of their surface, like the keels of the Chelonioido3, are seen very early. (See 

 PI. 9c, fig. 13-17; PI. 15, fig. 7; and PI. 6, fig. 18-20.) The Emydoidae, on the 

 contrary, go on widening, (PI. 9c, fig. 20, 21, and PL 16, fig. 2,) and acquire a per- 

 fectly circular form, identical with that of the Trionychidaj at the time of hatching, 

 (PL 6, fig. 1-7,) before their most prominent fiimily characters begin to appear. This 

 shows plainly that the circular form is only a transient form with the Emydoidae, 

 while it marks the closing development of the form of Trionychidas, and is not 

 even reached by the Chelonioidae and Cinosternoidas. In Chelydroida3, on the con- 

 trary, the circular form is already accompanied by all the prominent flimily char- 

 acters, (PL 15, fig. 1-3,) as in Trionycliida^, long before they are hatched.^ 



^ The legs also elongate early into a I'orni approx- 

 imating that of paddles. PI. 6, fig. 20. 



2 In Part I., Chap. 2, Sect. 8, p. 172 to 176, I 

 have already discussed the subject of the successive 

 development of the characters in a general way. 

 The particular results obtained from the study of the 

 Turtles deserve, however, a special notice. We have 

 seen that, at a very early period, the embryo of Tur- 

 tles presents all the characteristics of a vertebrated 

 animal. But, even before it can be recognized as a 

 Vertebrate, the germ has already acquired the inde- 

 pendence of a new being. It is an individual, free 

 from its parent, before it even shows to what branch 

 of the animal kingdom it belongs. This exemplifies 



strikingly the importance of individuality as the most 

 prominent feature in every organic development. 

 But individuality is not only characteristic as the pri- 

 mary step in the growth of every living being ; it re- 

 mains also characteristic through life, so much so in- 

 deed, that individual peculiarities are superadded even 

 to the highest features of their race, in almost every 

 individual, to whatever species he may belong. Thus 

 Nature herself teaches us the true value and dignity 

 of individuality. This shows plainly how contrary to 

 the law of organic growth must be every restraint, 

 whether natural or artificial, which does not foster the 

 highest development of the species. (Under natural 

 restraint, I would consider the influence of physical 



