THE DIAMOND-BACK TERRAPIN. 95 



ing influence on normal spring feeding and growth in the terrapins, may possibly be 

 the causes of the decreased productiveness, though a similar decrease is not found in 

 the egg production of the original brood stock. The 1920 decrease shown in Table 1 

 is due in part to the destructiveness of the rats above referred to and probably also 

 to a very late spring, the first eggs being laid on May 17, a rather late date. Many 

 of the brood terrapins, however, did not lay their first eggs of the season until the mid- 

 dle of June, more than a month after the usual first egg-laying date. In 1917 certain 

 of the females of the second lot of breeders were set aside for experimental purposes, 

 and this had a tendency toward diminishing the actual number of young produced, 

 while the experiments yielded information which is of value from other aspects and 

 will be discussed later. Because of this experimental work the figures for "young" 

 in the table are estimates and are included only tentatively in the 1918 and 1919 records. 

 The mixing of part of the first lot with the entire second lot of breeders in 191 8 and 19 19 

 made it necessary also to estimate the number of eggs laid by both these lots, and these 

 records have been so noted. 



The estimation was possible in view of the fact that a considerable proportion of 

 the original brood stock was not mixed with the second brood stock. The method 

 followed to obtain the estimated records was this. One lot of the original brood stock 

 (lot A) was held in a separate pen during the year, and from the egg and young produc- 

 tion of this lot was computed an average egg and young production for the entire original 

 brood stock. From this computation it was possible, then, to figure the production 

 of those terrapins (lot B) of the original brood stock which had been penned with the 

 second brood stock. The egg and young production of the entire second brood stock 

 (lot C) was ascertained by subtracting the egg and young production of lot B from the 

 total egg and young production of lots B and C combined, lot B plus lot C representing 

 the mixed lots of brood stock. 



In 1920 the terrapins of the first and second lots of breeders were so mixed that it 



was impossible to estimate at all accurately the egg production of either lot, and for 



this reason the egg production and hatch of these broods for 1920 are combined. The 



combined egg and young production record, though lower than that of either lot in 



the preceding year, is not significant, however, because of the heavy egg destruction 



caused by rats. 



TEXAS BROOD STOCK. 



The Texas brood stock, with average length in the spring of 1920 of 177 mm.' 1 and 

 probable age of 30 years, has shown an increasing productiveness annually since its first 

 laying in confinement until 1920, when doubtless, as above, the decrease in the egg and 

 voung production record was due to destruction of eggs by rats. In 1919 from 1 1 adult 

 females of this stock which had been used in hybrid studies with Carolina males there 

 were obtained 270 eggs, or 24.5 eggs per female. In 1916 all but 12 of the Texas terra- 

 pins were returned to Texas. The 1 2 that remained were the finest and largest females 

 of the original Texas lot, and the exceptional egg production of the 1 1 mentioned above 

 mav be due to this fact. It is understood that when the entire Texas brood stock was 

 at Beaufort the average number of eggs produced per female was lower than for either 

 of the Carolina lots'. 



B Approximated Irom measurements recorded in inches. 



