v.] IN THE THEORY OF NATURAL SELECTION. 327 



communication of such traumatic and therefore acquired epi- 

 lepsy to the germ-cells. This is obviously impossible under 

 the epigenetic theory of development described above. In 

 what way can the germ-cells be affected by molecular or histo- 

 logical changes in the pons varolii and medulla oblongata? 

 Even if we assume, for the sake of argument, that the central 

 nervous system exercises trophic influences upon the germ- 

 cells, and that such influences may consist of something more 

 than variations in nutritive conditions, and may even include 

 the power of altering the molecular constitution of the germ- 

 plasm in spite of its usual stability; even if we concede these 

 suppositions, how is it conceivable that the changes produced 

 would be of the exact nature and in the exact direction necessary 

 in order to confer upon the germ-plasm the molecular structure 

 of the first ontogenetic stage of an epileptic individual ? How 

 can the last ontogenetic stage of the ganglion cells in the pons 

 and medulla of such an individual, stamp upon the germ-plasm 

 in the germ-cells of the same animal — not indeed the peculiar 

 structure of the stage itself^but such a molecular constitution 

 as will ensure the ultimate appearance of epilepsy in the off- 

 spring ? The theory of epigenesis does not admit that the parts 

 of the full-grown individual are contained in the germ as pre- 

 formed material particles, and therefore this theory' cannot allow 

 that an3thing is added to the germ-plasm ; but in accepting the 

 above-made supposition, we are compelled to assume that the 

 molecular structure of the whole of the germ-plasm is changed 

 to a slight extent. 



Nageli is quite right in maintaining that the solid protoplasm 

 alone, as opposed to the fluid part, i. e. that part of the proto- 

 plasm which has passed into solution, can act as the bearer of 

 hereditary tendencies. This appears to be undoubtedly proved 

 by the fact that the amount of material provided by the male 

 parent for the development of an embryo is in almost all animals 

 far smaller than the amount provided by the female parent. 



In Mammalia the share contributed by the father probably 

 only forms about one hundred-billionth part of that contributed 

 by the mother, and yet nevertheless the influence of the former 

 in heredity is on an average equal to that exerted by the latter^ 

 Now, from the point of view of epigenesis, no molecule of the 



* Nageli, 1. c. p. no. 



