14 CALIFORNIA ACADEMY OF SCIENCES. 



mann simply means that an organism has the potential 

 power of renewing the cycle of its existence, as long as 

 the environment conditioning its existence remains 

 suitable. While it can be destroyed, it does not bear 

 within it the seeds of decay. ''If, then," says Prof. 

 Weismann, " this true immortality is but cyclical, and 

 is conditioned by the physical constitution of the pro- 

 toplasm, why is it inconceivable that this constitution 

 should be under certain circumstances and to a certain 

 extent, so modified that the metabolic activity no longer 

 follows its own orbit, but after more or fewer revolutions 

 comes to a standstill and results in death? All living 

 matter is variable; why should not variations in the 

 protoplasm have occurred which, while they fulfilled cer- 

 tain functions of the individual economy better, caused 

 a metabolism which did not exactly repeat itself, i. e., 

 sooner or later came to a condition of rest?" 



This explanation, although rather vague, does indeed 

 seem to throw some light upon the way in which mortal- 

 ity might have originated, but his appeal to panmixia 

 to aid him seems wholly unwarrantable. He s&ys: " I 

 believe that organs no longer in use become rudiment- 

 ary, and must finally disappear solely by 'panmixie'; 

 not through the direct action of disuse, but because 

 natural selection no longer maintains their standard of 

 structure. What is true of an organ is true also of its 

 function, since the latter is but the expression of the 

 qualities of material parts, whether we can directly per- 

 ceive their relations or not. If, then, as we saw, the 

 immortality of monoplastids depends on the fact that 

 incessant metabolism of their bodies is ever returning 

 exactly to its starting point, and produces no such modi- 

 fications as would gradually obstruct the repetition of 

 the cycle, why should that quality of its living matter 

 which causes immortality — nay, how could it be re- 



