The first of the facts generally said to support the view that the nucleus of the germ-cells exerts a specified influence upon the processes of development and inheritance, relates to the proportion between protoplasm and nuclear material in the egg and in the spermiae. This proportion is very different in the two sexual products, as we know, there being an enormous preponderance of the protoplasm in the egg, of the nucleus in the spermatozoon. This seems to indicate that the proportion between protoplasm and nucleus is fairly indifferent for inheritance, as all the facts go to show that inheritance from the father is as common as inheritance from the mother. It is in the nucleus, and in the nucleus alone, that any similarity of organisation exists between the two sexual products, so very different in all other respects: therefore the nucleus should be the organ of inheritance. The phenomena of nuclear division, of karyokinesis, which are quite equal in both sexual cells, are certainly well fitted to support this hypothesis. There seems indeed to be some truth in this reasoning, but nevertheless it must remain hypothetical; and it must never be forgotten that there may be very probably some sort of morphogenetic importance in protoplasm also. Rauber and afterwards Boveri[135] have tried to prove experimentally that it is on the nuclear chromatic substance only that inheritance depends, but the first of these authors failed to get any results at all, and the latter obtained only ambiguous ones. Godlewski, on the contrary, has fertilised purely protoplasmic egg-fragments of the sea-urchin with the sperm of quite another group of Echinoderms, and obtained in spite of that a few stages of development of the pure maternal type. This experiment seems to place the morphogenetic importance of protoplasm beyond all doubt. [135] Boveri tried to fertilise enucleated fragments of the egg of *Sphaerechinus* with the sperm of *Echinus*. He failed to get any results in isolated experiments, but found a few small larvae of the pure *Echinus* type in large cultures consisting of shaken eggs. But later experiments on hybridisation in sea-urchins have shown that a full hybrid of *Echinus* and *Sphaerechinus* may be purely paternal also. I should prefer not to make any definite statement about our problem at present. Our actual knowledge of the organisation and metabolism of both nucleus and protoplasm is so extremely small and may relate to such very insignificant topics, that any definite decision is impossible. I myself believe that the nucleus plays an important part in heredity, perhaps even a greater one than protoplasm, but this is only my belief.[136] [136] Surely the new results of Herbst, mentioned above, are another indication of the importance of something in the nucleus. The first stage in parthenogenesis, which he used in his experiments, is a nuclear phenomenon.