148 The Science of Life. 



perfect representation of his own stirp, and the personal 

 structure of each of the parents is no more than an im- 

 perfect representation of each of their own stirps." 



This is a definite expression of the notion that the 

 germinal cells of the offspring- are in direct continuity 

 with those of the parents. The antithesis between the 

 "soma" and the chain of sex-cells is emphasized. 



The history must also include Nussbaum, who called 

 emphatic attention to the very early differentiation and 

 isolation of the sex-elements to be observed in some 

 cases. The theory both of Jaeger and of Nussbaum is 

 that of a continuity of germinal cells. The theory of 

 Weismann is more strictly that of the continuity of 

 germinal protoplasm. 



The idea of a continuity of germ-cells may now be 

 summarized more definitely : 



(1) At an early stage in the embryo, the future reproductive 

 cells of the organism are often distinguishable from those which 

 are forming the body. 



(2) The latter develop in manifold variety, and lose almost all 

 likeness to the mother germ. 



(3) The former the reproductive rudiments are not impli- 

 cated in the differentiation of the "body", remain virtually 

 unchanged, and continue the protoplasmic tradition unaltered. 



(4) As the sex-cells of the offspring are thus continuous with 

 the parental sex-cells which give rise to it, they will in turn 

 develop into similar organisms. 



This fact of the continuity of reproductive elements 

 is obviously of fundamental importance. If a fertilized 

 egg-cell has certain characters, a, b, c y x, y, z, it develops 

 into an organism in which these characters, a, b, c, x,y, z, 

 are expressed; but, at the same time, the future repro- 

 ductive cells are early set apart, retaining the characters 

 a, b, c, x,y y z, in all their entirety, to start a new organ- 

 ism again with the same capital. Balbiani, who was 

 not influenced by theoretical considerations, observed 

 in the development of the blood-worm or Chironomus 

 (an insect) that the future reproductive cells were iso- 

 lated before even the blastoderm was completed; that 

 is to say, at a stage when hardly any differentiation had 



