78 REMARKS ON CERTAIN [XI. 



have arisen in the latter which rendered possible more 

 energetic assimilation, but which was accompanied by an 

 expenditure of nutriment, and which, after the lapse of a certain 

 time, involved the complete cessation of assimilation, and con- 

 sequently the death of the organism. 



The conception of a change in the protoplasm which involves 

 the loss of immortality is to my mind no more improbable or 

 more difficult than the commonly received view of the differen- 

 tiation of somatic cells which gradually takes place in their 

 phylogeny, by which they are enabled to assume various 

 natures, i. e. absorptive, secretory, muscular, nervous, &c. An 

 unchangeable immortal protoplasm does not exist, only an 

 immortal ' form of activity ' in organic matter. 



Thus my former statement, that unicellular organisms and 

 the reproductive cells of higher forms do not suffer natural 

 death, is maintained in its entirety ; and I know of no better 

 way to give expression to this idea than to say that such 

 structures possess immortality, that is real, true immortality, 

 not the phantastic, visionary immortality of the old Greek gods. 

 If then death from internal causes has no existence for the 

 organisms and structures in question, we can nevertheless 

 maintain with absolute certainty that every one of them will 

 come to an end, not indeed by the operation of forces from 

 within, but because the external conditions which are necessary 

 for the constant renewal of vital activity must at some future 

 time themselves cease to be. The physicist predicts that the 

 circulation of water on the earth will at some time inevitably 

 cease, not because of any change in the nature of water, but 

 because external conditions will render impossible this kind of 

 movement of its particles. 



Professor Vines then attacks my views on embryogeny. He 

 finds it ' not a little remarkable that Professor Weismann should 

 not have offered any suggestion as to the conception which he 

 has formed of the mode in which the conversion of germ-plasm 

 into somatoplasm can take place, considering that this assump- 

 tion is the key to his whole position \' He finds in this the 

 same difficulty as in the phyletic development of multicellular 

 from unicellular organisms. He concludes his objection with 

 the words, 'There is really no other criticism to be made on an 

 1 ' Nature,' Oct. 1889, p. 623. 



