318 THE SIGNIFICANCE OF SEXUAL REPRODUCTION 



to be the cause of the subsequent appearance of the peculiarity 

 in the mature animal. It is only by the aid of some such hypo- 

 thesis that we can conceive the cause of hereditary individual dif- 

 ferences and the tendencies towards hereditary diseases. Hereditary 

 epilepsy would be intelligible in this way, that is, when the disease 

 is congenital and not due to the presence of microbes, as is pre- 

 sumably the case with artificially induced epilepsy. 



The question now arises as to whether we can conceive the 

 communication of such traumatic and therefore acquired epilepsy 

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

 genetic theory of development described above. In what way 

 can the germ-cells be affected by molecular or histological 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 con- 

 ditions, 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 offspring? The theory of epigenesis does not admit that 

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

 preformed material particles, and therefore this theory cannot allow 

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

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

 cular 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 protoplasm 

 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 de- 



