VITALITY 



491 



differentiations at maturity. The most significant of these age dif- 

 ferentiations are: (1) Greatly reduced vitaHty; (2) structural differ- 

 entiations; (3) abnormal divisions leading to monster formation; (4) 

 special structures appearing at no other time in the life cycle. 



Fig. 204. — Vitality graphs showing the limited period of encystment (between 

 the two irregular vertical single lines), and the periods at which conjugation begins 

 (double line) in ten different series of Uroleptus mobilis. (Original.) 



The best evidence of reduced vitality towards the end of the 

 cycle is afforded by Uroleptus mobilis and Spathidium sixitJmla. In 



