42 THE ORGANIC GROWTH OF THE LIVING WORLD SEC. 



spermatozoon must be adapted with perfect accuracy to the 

 morphological peculiarities of the egg-envelope if there are to 

 be no morphological hindrances, even the minutest, to fer- 

 tilisation. For the formation of new species in this way 

 it is therefore only necessary that the sperms and the 

 eggs of a given number of individuals should have pecu- 

 liarities of structure corresponding with one another, and 

 not corresponding with those of others. Complete isola- 

 tion of the varying individuals is thus on these grounds 

 also not absolutely necessary for the formation of new 

 species. 1 



The correlative alteration of the sexual products leads to 

 the consideration of a fact which seems to me to cry loudly 

 against Weismann's assumption that those products remain 

 essentially unaffected by the condition of the body from time 

 to time. I refer to the great correlative influence which con- 

 versely the condition of the sexual products, namely, their 

 maturity (puberty) and their artificial removal (castration), as 

 well as the extinction of their powers in old age, has upon the 



go so far as to doubt that the character of the process of fertilisation is that of a 

 physico-chemical, i.e. physiological, process, let us rather, I say, leave the problem 

 of atavism for the present unsolved. What if the solid nuclear substance had the 

 power to reproduce the condition of the whole body at any given moment because 

 it was definitely and peculiarly adapted to contain an extract, as it were, of the. 

 whole body ? Who will undertake to prove that it does not take up such an ex- 

 tract somewhat like a delicate sponge, so that the inheritance of acquired char- 

 acters, as in the older view, can be physiologically explained in spite of its firm 

 structure ? In any case, such a hypothesis is not in contradiction to general 

 physiological principles, as the conception of fertilisation as a purely morpho- 

 logical process seems to me to be. 



Weismann, moreover, speaks in his more recent paper (Bedentung der 

 sexuellen Fortpflanzung) of an increase of the germ-plasm by assimilation ;>but 

 such assimilation merely on the ground of the laws of physiology obviously im- 

 plies that the germ -plasm is influenced by the general nourishment in other 

 words, by the condition of the body. 



1 Apart from this I have shown in reference to this question in a very carefully- 

 studied example in the wall-lizard that varieties differing to any important 

 degree fight with one another when they live together, as if there was profound 

 antipathy between them ; that, therefore, they do not sexually mingle, while the 

 similar individuals breed together, and so establish their characters more firmly. 



