Aging in Coelenterates 



Bernard L. Strehler 



Gerontology Branch, National Heart Institute, National Institutes of Health, 

 PHS, Department of Health, Education t~ Welfare, Bethesda, and the Baltimore 

 City Hospitals, Baltimore, Maryland. 



Aging may be defined as the deerease in the funetional capacity 

 of an organism following its attainment of reproductive maturity 

 (27). According to this definition, aging is not a continuation of 

 development for aging generally expresses itself in a given species 

 as an increase in the probability of death, whereas de\'elopment 

 leads to increased functional capacity. 



Different species of animals and plants age in different ways 

 (21). They age in accord with evolutionary forces, for length of 

 life, like other features of organisms, is an adaptation, at least in 

 part, to the niche which an organism occupies. Aging comparable to 

 that occurring in man and other metazoans probably makes its first 

 appearance in the coelenterates. There appeared to be controversy 

 for some time regarding the presence or absence of aging processes 

 in Hydrozoa, particularly in hydra ( 7 ) . Boecker ( 4 ) , Berninger 

 (2) and Hertwig (19) found that their cultures of hydra underwent 

 a depression with accompanying cytological changes. However, 

 Goetsch ( 15 ) improved culture conditions and kept individuals of 

 Pelmatohydm oligactis and another species alive for 27 months. He 

 believed that hydra, as well as Actinians, were capable of main- 

 taining themselves in status quo indefinitely. Gross (16), on the 

 other hand, failed to keep any individual of P. oligactis alive for 

 more than about a year and noted changes which he called "senile" 

 beginning at about the fourth month of life. Pearl and Miner (23) 

 used Hase's data (18) to construct a life table for hydra. David 

 (11) kept records of P. oligactis and was convinced that the in- 

 dividual animals tended to die between 20 and 28 months. However, 



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