The Distribution of Senescence 



and Lynch (1928) had already noted that the offspring of very 

 old rotifers are less viable than those of vigorous adults. Lan- 

 sing's results suggested that the effects of maternal age are 

 cumulative from generation to generation: they were also 

 reversible, the eggs laid by young members of such a clone 

 being capable of giving rise to normally long-lived individuals. 

 Lansing also found that clones propagated in each generation 

 from the eggs of very young mothers showed an increase in 



35 40 



DAYS 

 Fig. 23. — Progressive decline in life-span of a strain of Philodina citrina 

 (Rotifera) raised in each generation from eggs laid by old mothers (from 



Lansing, 1952). 



longevity over the control stock. In Euchlanis triquetra, the 

 'young' orthoclone could not be maintained, however, because 

 within a few generations it gave rise largely to male-producing 

 eggs. Lansing regards his ageing-factor as a product of growth- 

 cessation, since it appears in the individual animal at the point 

 where the negative specific acceleration of growth is greatest. 



The susceptibility of rotifer eggs to external influences affect- 

 ing the life-cycle of the progeny has been much studied in forms 



89 



