The Biology of Senescence 



The somatic growth of rotifers has been studied by several 

 workers. Rotifer vulgaris shows little or no change in size through- 

 out life (Spemann, 1924). The growth curve of Apsilus vorax is 

 a parabola, with shrinkage before death (Cori, 1925) while in 

 Philodina citrina growth ceases by the sixth day (Lansing, 1948). 

 (See Fig. 21.) Lansing also made the striking observation that 



30 



20 § 



10 



10 



15 



20 



DAYS 



25 30 35 



Fig. 22. — Life-span and egglaying of Philodina citrina (Rotifera) over 6 

 generations in normal culture (from Lansing, 1952). 



if these rotifers are propagated in each generation from eggs 

 laid at or after the fifth day of maternal life, the rate of develop- 

 ment becomes progressively greater and greater from genera- 

 tion to generation, and the longevity of the individual less and 

 less, so that clones propagated in each generation from old 

 mothers invariable become extinct (Figs. 22, 23, 24). Jennings 



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