The Biology of Senescence 



Among chelonians, both patterns of growth are known to 

 occur. Continuous growth as a decreasing rate appears to be 

 general in tortoises, the large species having inherently higher 

 growth rates throughout. Townsend (1931, 1937) found that 

 early growth in 100 specimens of the large T. vicina, kept in 

 captivity, was potentially very rapid, and continued after the 

 age of sexual maturity (about 20 years of age). Flower (1945) 

 observed continuing growth in a 39-year old specimen of 

 T. graeca. The age of sexual maturity in the male Terrapene 

 Carolina appears to lie between 12 and 15 years (Nichols, 1939). 

 All these are known to be long-lived forms. On the other hand, 

 the majority of terrapins exhibit specific size. In Emys Sergeev 



18 



c 



-C 



I 



YEARS 



Fig. 19.— Growth of Emys (Sergeev, 1937). 



(1937) found that growth-cessation by the fifteenth year of life 

 was as complete as in the adult mammal (Fig. 19) although E. 

 orbicularis, like T. graeca, is apparently capable of living 70-120 

 years and probably of breeding throughout life (Flower, 1937). 

 Rollinat, however, on whose observations Flower's records were 

 based, considered that growth in this form might continue for 

 30-40 years (Rollinat, 1934). Hildebrand (1932) studied the 

 longevity and growth of over 1,000 specimens of Malaclemmys 

 centrata in captivity — an investigation which is the nearest pub- 

 lished approach to a chelonian life-table, but which was unfor- 

 tunately continued in detail for only 10 years. He found the age 

 of maturity much more variable than in mammals, some indi- 

 viduals being full-grown in 8-9 years, others requiring 12-15. 

 The oldest specimens in captivity were 21 years old, and 



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