294 



AMERICAN TESTUDINATA. 



Part II. 



Testudinata undergo with age, not only because I have been able to obtain a 

 much larger number of specimens, but chiefly because I have had ample oppor- 



carapace of a Trionyx, and that like tliis, it lives 

 almost exclusively in water. This is also the 

 reason why, in spite of the much larger number of 

 young than of adults, (which exist no doubt among 

 these animals, as in most species throughout the 

 animal kingdom,) the young Emydoidoe are still so 

 rare in our museums, and almost unknown to zoolo- 

 gists. Nothing could prove more directly this differ- 

 ence in the mode of life of the young and the adult 

 than the fact, that though Emys insculpta is so com- 

 mon in the neighborhood of Lancaster, about forty 

 miles from Boston, that 1 have at times collected 

 over one hundred in an afternoon, aided by a few 

 friends, I have never yet been able to obtain a 

 single young specimen of the first year, even though 

 a whole school of young men were called to aid in 

 the search. Professor 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. 



By and by the bulk of the body becomes more 

 concentrated in the middle ; the lungs of land species, 

 being larger in proportion than those of aquatic 

 ones, (see above, p. 283,) require a larger develop- 

 ment of the carapace in height ; and Emys picta 

 of the seventh year, which is now ready to go from 

 time to time on land, assumes at this age the shape 

 of the Nectemyds. Then it approaches more and 

 more the rounded form of the land Turtles ; this 

 is, however, never reached in this species, though it 

 is actually the case in a higher genus of Emydoida3, 

 the terrestrial Cistudo. 



The retrograde development of the tail, as shown 

 in our table, furnishes another proof of the truth 

 of these comparisons. At first, in the hatching 

 Turtle, the tail is vertical, compressed laterally, and 

 very long in proportion to the size of the animal, 

 indeed, nearly as long and powerful as in Chelydra, 

 and, like the tail of a Tadpole, serves as a kind of 



rudder, strong enough to direct the course of that 

 living flat-boat with its four paddles. Thus, as 

 in the flying Bird, the tail is to be looked upon as 

 a locomotive organ. But afterwards it does not 

 grow in the same proportion as the body ; and 

 while in the young it was one of its most im- 

 portant parts, it is, on the contrary, in the adult, 

 a mere appendage to the body, weak and useless 

 for the locomotion of that heavy bulk. I may 

 add here, that the tail is also rather long in Triony- 

 chidai ; and that in the family of Chelydroida? it 

 is most powerful, and clearly subservient to loco- 

 motion, in darting the body forwards or in turning 

 it over when on its back ; while in Cistudo it nearly 

 disappears, or at least loses all significance. 



Again, the legs, in their development in the young 

 as compared with the adults, show similar meta- 

 morphoses, though not in the same degree in our 

 species as in some others, E. guttata or insculpta, 

 for instance. Being really broad paddles in the 

 young, they become stifFer and more compact in 

 the adult, to suit their habit of walking on the land, 

 as well as swimming in the water. In Cistudo, 

 the highest Emydian, they have reached the form 

 of feet adapted to walking, instead of broad paddles, 

 and so we find the slender fingers soldered together. 

 In one species of this genus, one of these fingers 

 has even faded away to a single phalanx, which 

 does not reach beyond the skin, or only shows, when- 

 young, a very small nail projecting sideways. 



We now proceed to a comparison of the horny 

 plates of the young E. picta with those of the adult. 

 I would also refer to the Plates I., II., III., and IV., 

 which exhibit accurate drawings of the young of a 

 number of other species of our Turtles. PI. XXVI. 

 represents, besides, several young Ptychemys rugosa, 

 (Emys rubriventris,) and PI. XXVII. adults of 

 the same species in different varieties of color. 

 A glance at the horny plates of both shows a great 

 difference in form. The following changes take place 

 in the development of these plates in Chryserays 

 (Emys) picta. The plates of the dorsal side of this 



