222 SECRETS OF ANIMAL LIFE 



in function (use and disuse), or in environment and 

 nurture generally, ever affect the germ-plasm in the 

 reproductive organs in such a specific or representa- 

 tive way that the offspring will thereby, though not 

 subjected to the nurtural peculiarity in question, 

 exhibit the same modification that the parent 

 acquired, or even an approximation towards it? 

 Modifications are dints of direct extrinsic origin, in 

 contrast to variations or mutations which are ex- 

 pressions of germinal change fulness; and the pre- 

 cise point is whether the acquirer of the modification 

 can entail it on his progeny as such or in any repre- 

 sentative degree. It is admitted that deep dints 

 may have secondary effects on the germ-cells and 

 on the unborn offspring; but this is not the question 

 at issue. It is also probable that long-continued, 

 deeply-saturating peculiarities of nurture may 

 produce substances that enter into the germ-cell 

 or into the embryonic body (e.g. the mammal in 

 its ante-natal life of symbiosis with its mother, or 

 the unliberated seed of the flowering plant), but 

 there is as yet no convincing evidence that the 

 resulting changes grip the constitution permanently. 

 It would perhaps facilitate our understanding of 

 organic evolution if we found reason to believe that 

 at least some advantageous modifications, hammered 

 on to the individual, could be transmitted ever so 

 little, but the difficulty is to find convincing evi- 

 dence. So it has come about, not through any 

 preference of darkness to light, but by pressure of 

 hard facts, that the majority of naturalists now 



