VITALITY—UROLEPTUS MOBILIS 305 
extremely high vitality agree in derivation from parents which 
were in the period of youth at the time of conjugation. 
Continued in-breeding has not, as yet, shown any deleterious 
effect on the vitality of the protoplasm under observation. ‘There 
is some evidence that congenital weakness of an F; generation due 
to old-age conjugations of the parents is inherited by the off- 
spring in the F, generation. 
Columbia University, 
March 10, 1920. 
