26 HEREDITY 



single cell from which all the higher animals and 

 plants are developed] gives rise in development to 

 two sets of elements — to the somatic cells [soma — 

 the body], which become differentiated into the 

 various tissues of the body, and to a lineage of non- 

 specialised germ-cells, some of which will eventually 

 be separated off to begin a new generation." 



Here we have an idea of cardinal importance. 

 Ideally stated, the sequence — actually observed in 

 many animals — is as follows : — The germ-cells and 

 the body-cells grow up side by side. The germ-cells 

 are shed and give rise again to a new body and to 

 their own undifferentiated descendants, which that 

 new body temporarily shelters. The germ-cells are 

 " immortal " ; the individual is merely a temporary 

 host which shelters a few generations of the germ- 

 cells, whose unbroken continuity constitutes the 

 race. Plainly the likeness of daughter and mother 

 begins to be intelligible. The germ-cells of the 

 mother — which will develop into her daughter — are 

 directly continuous with the cells which gave rise 

 to the body of the mother. "As the sex-cells in 

 an offspring are thus genetically continuous with 

 [i.e. directly derived from] the parental sex-cells 

 which gave rise to it, they will in turn develop into 

 organisms like the parent — a conception fundamental 

 to an understanding of inheritance and development." 

 On this theory of Weismann we must regard each 

 individual as merely the temporary host of the con- 

 tinuous line of germ-cells which constitute the race. 



Now in many of the lower animals the actual 

 unbroken sequence of the germ -cells, from one 

 generation to another, can positively be detected. 



