1922] Phases in the Development of Chrysemys Cinerea 57 



The eggs deposited by different individuals vary in number from 

 four to fourteen, with an average of seven. Inasmuch as the size 

 of a turtle is an indicator of its age, comparisons were made to deter- 

 mine whether there is any relation between the age of the turtle and 

 the number of eggs laid. No definite relation is apparent if isolated 

 cases be studied but when the average production of the various 

 sizes is taken a gradual increase in egg number occurs with in- 

 creasing size, as is shown in the following table: 



The size at which turtles begin to lay is not at all uniform. In 

 C. picta, Agassiz states that copulation begins about the seventh 

 year and egg-laying about the eleventh, or at the time that the tur- 

 tle has reached 80 mm. in length. He estimates that other species 

 begin to lay when from eleven to fourteen years of age. Newman 

 (1906) says of Graptemys, that he has never found one nesting when 

 less than 190 mm. in length, or when about fourteen years of age. 

 In C. cinerea nesting may begin when the carapace length is only 

 1 30 mm. ; but oviposition may be delayed until after the length is 

 150 mm. In the case of one specimen, 187 mm. long, an examination 

 of the ovary revealed the presence of only very small eggs, indi- 

 cating that the turtle would not lay within a couple of years. This 

 case may have been abnormal. 



In some species it is possible to determine the age of turtles by 

 the growth rings on the dorsal plates, much as the age of the fish 

 is determined by the growth rings upon the scales. This method 

 is not applicable to C. cinerea since in this species no growth rings 

 are evident. Agas.siz noted these rings on some species which he 

 does not name and used a novel method of calculation. Forms in 

 which the rings occurred were measured and from the number of 

 growth rings he determined the age. This standard of measure- 



