74 Scientific Proceedings, Royal Dublin Society. 



the higher organism and its offspring as a continuous and pro- 

 gressive whole ; and in the growth of the offspring we see the con- 

 tinued growth of the parent. The individuals perishing one by- 

 one are but the aborted limbs, which under new conditions became 

 functionless. 



Professor Weismann, in his two essays, " The Duration of 

 Life," and " Life and Death,"i adopts and defends the view that 

 " death is not a primary necessity but that it has been secondarily 

 acquired by adaptation." The cell was not inherently limited in 

 its number of cell-generations. The low unicellular organisms are 

 potentially immortal, the higher multicellular forms with well- 

 differentiated organs contain the germs of death within themselves. 

 According to Professor Weismann, however, the means by which 

 death entered organic history are not such as I have discussed in 

 the foregoing pages. 



Briefly he finds the necessity of death in its utility to the 

 species. Long life is a useless luxury. Early and abundant re- 

 production is best for the species. An immortal individual would 

 gradually become injured and would be valueless or even harmful 

 to the species by taking the place of those that are sound. Hence 

 natural selection will shorten life. 



According to the preceding views a periodic effect is necessary 

 to introduce an inherited time-limit into a species, and this effect 

 must be of such a nature as will operate on the individual so as 

 gradually to affect the germ, and so become hereditary. 



Against such a hypothesis Weismann contends, " because it 

 involves the transmission of acquired characters which is at 

 present improved."- He bases the appearance of death on 

 variations in the reproductive cells, encouraged by the ceaseless 



1 See tis " Biological Memoirs." Oxford, 1889. 



^ " Biological Memoirs," p. 142. A somewhat similar explanation to that suggested 

 in foregoing pages of the origin of old age and death — but differing in many par- 

 ticulars — -was advanced by Dr. Wallace. See a note on p. 23, of the " Biological 

 Memoirs." I Lad sketched out the above views before the latter work came into my 

 hands. It is possible that Professor Weismann would classify the particular mode in 

 which I have supposed the recurrent effect to become hereditary as not contradictory 

 to his theory of Heredity. In a later essay (" On the supposed Botanical Proofs of 

 the Transmission of Acquired Characters"), he appears to regard characters so impressed 

 upon the organism as "blasto-genic." See p. 413, "Biological Memoirs." 



