278 SIGNIFICANCE OF SEXUAI REPRODUCTION [V. 



modify the germ-cells, I nevertheless believe that they have no 

 share in the production of hereditary individual characters. 



The germ-plasm or idioplasm of the germ-cell (if this latter 

 term be preferred) certainly possesses an exceedingly complex 

 minute structure, but it is nevertheless a substance of extreme 

 stabilit}', for it absorbs nourishment and grows enormousl}'' 

 without the least change in its complex molecular structure. 

 With Nageli we may indeed safely affirm so much, although 

 we are unable to acquire any direct knowledge as to the con- 

 stitution of germ-plasm. When we know that many species 

 have persisted unchanged for thousands of years, we have 

 before us the proof that their germ-plasm has preserved exactly 

 the same molecular structure during the whole period. I may 

 remind the reader that many of the embalmed bodies of the 

 sacred Egyptian animals must be four thousand years old, and 

 that the species are identical with those now existing in the 

 same locality. Now, since the quantity of germ-plasm con- 

 tained in a single germ-cell must be very minute, and since 

 only a very small fraction can remain unchanged when the 

 germ-cell developes into an organism, it follows that an 

 enormous growth of this small fraction must take place in 

 every individual, for it must be remembered that each individual 

 produces thousands of germ-cells. It is therefore not too much 

 10 say that, during a period of four thousand years, the growth 

 of the germ-plasm in the Egyptian ibis or crocodile must 

 have been quite stupendous. But in the animals and plants 

 which inhabit the Alps and the far North, we have instances 

 of species which have remained unchanged for a much longer 

 period, viz. for the time which has elapsed between the close 

 of the glacial epoch and the present day. In such organisms 

 the growth of the germ-plasm must therefore have been still 

 greater. 



If nevertheless the molecular structure of the germ-plasm 

 has remained precisely the same, this substance cannot be 

 readily modifiable, and there is very little chance of the smallest 

 changes being produced in its molecular structure, by the 

 operation of those minute transient variations in nutrition to 

 which the germ-cells, together with every other part of the 

 organism, are exposed. The rate of growth of the germ-plasm 

 will certainly vary, but its structure is unlikely to be affected 



