284 DEATH 



no tendency to conjugate with each other, and 

 appear indeed to be incapable of doing so, for 

 attempts at such conjugation have been found to 

 prove abortive. 



By his method of isolating Infusoria and follow- 

 ing the fate of the successive generations produced 

 by fission, Maupas was enabled to prove that there 

 are natural and definite limits to the continuance 

 of asexual reproduction. An Infusorian, Stylonychia 

 pustulata, was isolated in November 1885, and the 

 successive generations followed until March 1886. 

 By that time there had been 215 generations pro- 

 duced by successive acts of fission. Conjugation 

 had not occurred, since nearly related individuals 

 will not conjugate, and unrelated forms were 

 excluded by the conditions of the experiment. 

 Towards the close of the experiment the tendency 

 to multiply by fission became less manifest, and the 

 individuals themselves were in a condition well 

 described as senescent ; they were of reduced size, 

 often distorted in shape, or actually malformed ; 

 their nuclear apparatus was in a degenerate con- 

 dition, and they no longer had the power, which 

 all the younger generations possessed, of conjugat- 

 ing effectively with unrelated individuals when 

 transferred to water containing such. Finally the 

 nutritive powers of these senescent members failed 

 and death of these exhausted forms brought the 

 experiment to an end. The same results were 

 obtained from experiments conducted in a similar 

 way with other Infusorians. The general conclu- 

 sions arrived at were : (i.) That in those Protozoa 



