The Distribution of Senescence 



depends directly upon metabolism — encysted rotifers can sur- 

 vive for very long periods (59 years — Rahm, 1923) and display 

 enhanced reproductive performance on emergence from dia- 

 pause (Dobers, 1915). 



It is particularly interesting that this dramatic senesence in 

 rotifers accompanies a very strict determinacy of cell number, 

 a lack of regenerative capacity, and in most species a very 



180 



Of 2 3 4 5 6 7 



Fig. 21. — Growth in length of Philodina citrina (Lansing, 1948). 



limited power of repair. Nuclear division after hatching has not 

 been described in any rotifer. In many forms wound healing is 

 confined to young animals — older animals die after amputation 

 (Pai, 1934) but in young Asplanchna brightwelli (Pai, 1934) and 

 Stephanoceros (Jurszyk, 1926, 1927; Ubisch, 1926) the cytoplasm 

 of the coronal lobes can be regenerated, as can parts of the 

 coronal funnel in Cupelopagis (Huhnerhoff, 1931; references 

 from Hyman, 1951). 



87 



