THE DIAMOND-BACK TERRAPIN. 



97 



laid fertile eggs each subsequent year until and including 1918. The record 

 production and hatch of these 10 terrapins through 19 18 is as follows: 



of 



egg 



In the spring of 1919, 5 males were introduced into this lot, and the fall produc- 

 tion was 137 young from 146 eggs. From this experiment it appears that female ter- 

 rapins may retain live spermatozoa in a health)' condition after a single copulation as 

 long as four years, and under such conditions some eggs laid even in the fourth year may 

 be fertile. It is apparent also that fertilization may occur immediately after copulation. 



In further consideration of the proper ratio of sexes for maximum fertility we have 

 the records of several domestic broods (Table 2) which, it happens, have contained 

 fixed ratios of males per 100 females throughout their existence. This set of observa- 

 tions includes lots in which the males number 5, 9, 12, 24, 32, and 50 per 100 females, 

 and the records give some suggestion of what may possibly be the most desirable ratio 

 of males to females to produce maximum fertility. 



Table 2. — .Sex Ratio and Fertility of the Diamond-Rack Terrapin in Captivity 



Egg-laying year. 



1909 hibernated brood 



First 



Second 



Third 



Fourth 



Filth 



Sixth 



1910 hibernated brood 



First 



Second 



Third 



Fourth 



Fifth 



i9ro selected brood: 



First 



Second 



Third 



Fourth 



Filth 



Sixth 



Males. 



Fe- 

 males. 



Males 

 per 100 



fe- 

 males. 



zoo 

 200 



50 



.10 



Eggs 



i id 



96 



11R 

 9* 

 119 

 138 

 140 



38 

 2tto 

 I 



f>40 

 42" 



»J 



4.X 

 ."9 



678 



4": 



Per 

 cent 

 fertil- 

 ity. 



Egg-laying year. 



77.8 



73-4 

 95- 7 



94- 7 

 89.2 



97 4 



»;. 4 

 91- -' 



75- o 

 61. 2 



81. s 



74.0 

 91. 2 

 9v 5 

 91. 5 



95- 7 



1910 winter -fed brood 



First 



Second 



Third 



Fourth 



Fif.h 



Sixth 



191 1 winter led brood 



First 



Second 



Third 



Fourth 



I-ath 



Sixth 



1912 winter-fed brood 



First 



Second 



Icrtil- 



>'y. 



83.3 

 78.6 

 90.5 



75- 4 

 45-9 



100. o 



0.0 



94 1 



93 S 



88.8 



91.4 



8s.  



In viewing the records of these broods it is necessary to bear in mind that maximum 

 fertility does not occur in the first year of laying in any brood unless there happens to 

 be laid only a very few eggs which may have, by chance, become fertilized. Accepting 

 90 per cent as normal fertility, it will be noticed that this per cent of fertility was reached 

 in the 19 10 hibernating brood in the third year of laying, and that this brood contained 

 only 5 males per 100 females. However, in the following year, when there were about 

 200 more eggs laid, the per cent of fertility dropped to 75. The fifth year, though 

 showing a decrease in fecundity in the terrapins, shows another considerable lowering 

 of percentage fertility. A similar drop in the per cent of fertility is also found in the 

 fifth and sixth years of laying of the 19 10 winter-fed brood after it had reached at least 

 90 per cent fertility in previous years. It was accompanied in the fifth year by an 

 7i;374° — 22 2 



