416 THE EVOLUTION THEORY 



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and therefore can never give rise again to the rank of germ-cells; 

 the others contain the latent germ-plasm intact, and can there- 

 fore produce not only cells like themselves for a certain time by 

 division, but have also the power, when they are mature and the 

 necessary conditions have been fulfilled, of bringing forth a new 

 individual of the same species. The former have only a limited 

 length of life, they die — they must necessarily die — when the life of 

 the individual to which they belong is at an end ; the latter are 

 potentially immortal, like the unicellular organisms, that is, they can 

 in favourable circumstances give rise to the germ-cells of a new 

 individual, and so on for all time, as far as we can see. The germ- 

 plasm of a species is thus never formed de novo, but it grows and 

 increases ceaselessly ; it is handed on from one generation to another 

 like a long root creeping through the earth, from which at regular 

 distances shoots grow up and become plants, the individuals of the 

 successive generations. If these conditions be considered from the 

 point of view of reproduction, the germ-cells appear the most im- 

 portant part of the individual, for they alone maintain the species, 

 and the body sinks down almost to the level of a mere cradle for the 

 germ-cells, a place in which they are formed, and under favourable 

 conditions are nourished, multiply, and attain to maturity. But the 

 matter can also be looked at in an opposite light, and then the endless 

 root of the germ-plasm, with its germ- cells ever forming new 

 individuals, may be regarded as the means by which alone nature 

 was able to create multicellular organisms, individuals of higher and 

 higher differentiation and capacity, able to adapt themselves to all 

 possible conditions, and to make the fullest use of all the possibilities 

 of life. 



interpret it — the whole of the germ-plasm is retained, while a part of it is withdrawn 

 from the soma. I have only partly described the process, and I do not wish to enter 

 in detail on an interpretation of it, since it seems to me obscure and to require 

 further observations before an interpretation can be attempted with any confidence. 



D. H. HILL LiehMi. t 



