9 6 



BULLETIN OF THE BUREAU OF FISHERIES. 



It is noteworthy in this connection that this maximum production for the Texas 

 stock is greater than that of the Carolina breeders. The maximum records of the two 

 stocks are as follows: Carolina, egg rate, 23.6; young rate, 21.4. Texas, egg rate, 24.5; 

 young rate, 22.4. 



The excessively cold winter of 191 7-18, which apparently slowed down output 

 among the feecond brood stock of Carolina terrapins, did not effect any retardation in 

 the productiveness of the Texas stock. The heavy decrease in recorded productiveness 

 of this brood stock in 1920 is due to destruction of eggs by rats, as in the case of the first 

 and second lots of Carolina breeders. 



RATIO OF SEXES AND FERTILITY. 



The number of males in a given stock of brood terrapins in each of these experimental 

 lots has been about one-third to one-half the number of females present. There appears 

 to be a negligible difference in the rate of young hatched per female in the different 

 broods with differing percentages of males present. A normal hatch appears to be about 

 90 per cent of the eggs laid, no matter how great a number of males may have been pres- 

 ent. It is needless to say that scarcity of males would, of course, increase the number 

 of infertile eggs laid. This percentage of infertile eggs is much larger at the beginning 

 of the laying period (fig. 79) of the terrapins and at the beginning of captivity (Table 1). 



The cause of the high infertile egg rate among terrapins which have laid for the first 

 time under our observation and have been penned with male terrapins of exactly their 

 age throughout their lives may be found in the fact that possibly the males do not reach 

 sexual maturity as early as the females. This is indicated in a study of certain lots of 

 terrapins experimented with during 1919. Seventy-eight female terrapins of the 1914 

 brood which had never laid fertile eggs, due to the fact that males had never been penned 

 with them, were separated into two equal lots which were kept in separate pens. With 

 one lot of 39 females were placed 3 males of the original brood stock at least 25 years 

 old; with the other lot were placed three 5-year-old males of the 1914 brood. This 

 division of the lot and introduction of males occurred on the same dav in earlv spring, so 

 that there might be plenty of opportunity for fertilization to occur before the egg-laying 

 period arrived. The production was as follows: 



Pen 9 . . 

 Pen 19. 



Females. 



Males. 



Age of 

 of males 

 (years). 



Eggs 

 laid. 



245 

 187 



Eggs 

 hatched. 



Per cent 

 fertile 

 eggs. 



54 

 152 



32. O 

 81.2 



Per cent 



infertile 



eggs. 



7S.0 

 18.8 



It is suggested from these data that males of 5 years are less potent than much 

 older ones and that maximum fertility may not be expected where young males, just 

 reaching sexual maturity, are used. 



In reviewing the entire matter of the most desirable numerical relation of males to 

 females in this species, it should be pointed out that mating among terrapins is pro- 

 miscuous. Copulation in one year may mean the production of fertile eggs for more 

 than that year alone. To cite a case under our observation, in 1914, 10 females of the 

 second lot of Carolina breeders which had been producing young were set aside in a 

 separate pen without males- With no further association with males, these terrapins 



