142 LIFE AND DEATH. [III. 



sense as a secondary appendage of the real bearer of life, — the 

 reproductive cells. 



Just as it was possible for the specific somatic cells to be 

 difterentiated from among the chemico-phj^sical variations 

 which presented themselves in the protoplasm, by means of 

 natural selection, until finally each function of the body was 

 performed by its own special kind of cell ; so it might be 

 possible for only those variations to persist the constitution 

 of which involved a cessation of activity after a certain fixed 

 time. If this became true of the whole mass of somatic cells, 

 we should then meet with natural death for the first time. 

 Whether we ought to regard this limitation of the life of the 

 specific somatic cells as a mere consequence of their differen- 

 tiation, or at the same time as a consequence of the powers of 

 natural selection especially directed to such an end, — appears 

 doubtful. But I am myself rather inclined to take the latter 

 view, for if it was advantageous to the somatic cells to preserve 

 the unending life of their ancestors — the unicellular organisms, 

 this end might have been achieved, just as it was possible at 

 a later period, in the higher Metazoa, to prolong both the 

 duration of life and of reproduction a hundred- or a thousand- 

 fold. At any rate, no reason can be given which would 

 demonstrate the impossibility of such an achievement. 



With our inadequate knowledge it is difficult to surmise the 

 immediate causes of such a selective process. Who can point 

 out with any feeling of confidence the direct advantages in 

 which somatic cells, capable of limited duration, excelled those 

 capable of eternal duration ? Perhaps it was in a better per- 

 formance of their special physiological tasks, perhaps in 

 additional material and energy available for the reproductive 

 cells as a result of this renunciation of the somatic cells ; or 

 perhaps such additional power conferred upon the whole 

 organism a greater power of resistance in the struggle for 

 existence, than it would have had, if it had been necessary to 

 regulate all the cells to a corresponding duration. 



But we are not at present able to obtain a clear conception 

 of the internal conditions of the organism, especially when we 

 are dealing with the lowest Metazoa, which seem to be very 

 rarely found at the present day, and of which the vital pheno- 

 mena we only know as they are exhibited by two species, both 



