9 4 BULLETIN OF THE BUREAU OF FISHERIES. 



arrived at from a knowledge of their size at the time of their purchase and of the num- 

 ber of years during which they have been captive in the experimental pens. They were 

 all adults at the time of their purchase, and the approximation of their age must be 

 quite accurate. From the knowledge that it takes at least much longer than nine 

 years for hibernating terrapins to reach an average length of 142 mm. (see Table 3) 

 and that after the length 142 mm. is reached the average annual growth increment, is 

 not more than 1.5 mm., it appears reasonable that the age of the terrapins of this brood 

 was at least 18 years in 191 1 (the year of measurement). 



Years. 



To reach average length of 142 mm 9 



To grow from 142 to 1 54 mm. (the 191 1 average length) 9 



From 191 1 to 1921 IO 



Total average age in 192 1 2 & 



2A- 

 20 

 16 



12 

 8 



1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 



Fig. 76. — Egg production per female in original and second Carolina and Texas brood stocks. , Original Carolina brood 



stock: , second Carolina brood stock; , Texas brood stock; * combined egg production per Icmale o( 



original and second Carolina brood stocks. Marked decrease in egg production probably due to destruction of eggs by rats. 



Inasmuch as maximum recorded egg production for this lot occurred in 1915, we 

 may presume, then, that maximum egg production occurs about the twenty-fifth year 

 of a terrapin's life. The actual maximum production of young, however, would, of 

 course, depend on the presence of sufficient males among the breeding stock. 



SECOND CAROLINA BROOD STOCK. 



The second lot of North Carolina breeders, with average measurement of 141 mm. 4 

 in 191 1 and probable average age of 9 years, has shown, with the exception of the years 

 1918 and 1920, a general increase in egg production since the beginning of its laying. 

 The 1918 record showed a dropping off in egg production of 2.1 eggs per female. The 

 reason for this decrease is problematical, but the exceptionally severe winter of 191 7-18 

 and the following late spring, with its resulting longer hibernation period and its retard- 



* Approximated from measurements recorded in inches. 



