Croonian lecture.—On the structural constituents of the nucleus, and their relation to the organisation of the individual

Abstract

The latter half of the nineteenth century witnessed three events of supreme importance to biology. The first of these consisted in that reasoned theory of the mode of origin of new species with which the name of Charles Darwin will always remain associated. The second lay in the discovery, made by Strasburger in 1875, that the nucleus is not only a permanent organ of the cell, but that certain definite constituents of it are transmitted in unbroken sequence from one cell generation to another. Thirdly, Oscar Hertwig, also in 1875, showed that fertilisation consists not only in the union of male and female cells, but that the union of the two nuclei forms an essential part of the process. At the present time, when evolutionary problems are being attacked at their very roots by the experimental study of variation, results are being accumulated which are capable of being dealt with from a cytological standpoint. Much is to be expected from a joining together of the forces engaged on what are really only different aspects of the same problem. What we really want to know is the nature and mode of working of the machinery which is responsible for the appearance of the characters manifested, as well as inherited, by the organism. We also are concerned with the nature of those inner changes which find their outward expression in what we designate as variation.