292 



AMERICAN TESTUDINATA. 



Part II. 



TABLE, 



SHOWING THE SUCCESSIVE CHANGES IN THE RELATIVE DIMENSIONS OF THE BODY IN EMYDOID^,. 



There is another feature which, though of less importance, still allows a gen- 

 eralization worth mentioning, I mean the change of color in Turtles of different 



^ As Turtles lay their eggs in the spring, the 

 specimens selected for examination were all collected 

 in the spring ; the starting point of comparison is, 

 therefore, really the second year of their develop- 

 ment. However, as the eclosion takes place only 

 late in the summer, the young had only been hatched 

 six months when picked up, though they are con- 

 sidered here as one year old, on account of the 

 long period of incubation. Moreover, there is very 

 little difference between specimens recently hatched 

 and those collected the following spring. 



^ After the seventh year, it is much more difficult 

 to distinguish the age of those Turtles, which, like 



Chrysemys picta, have a perfectly smooth epidermis, 

 than during tlie earlier years. I have, however, 

 been able to determine it with tolerable precision, 

 by collecting large numbers of specimens at the 

 same time and in the same season, and assorting 

 them according to their size, and comparing the 

 sets thus formed with specimens of other species, 

 in which the successive lines of growth indicate the 

 number of their years. During the first six or seven 

 years the rate of growth is so uniform that numer- 

 ous specimens collected at the same time are readily 

 arranged in sets of the same age, simply by the 

 difference they show in their size. 



