446 



Croonian Lecture. — On the Structural Constituents of the 

 Nucleus, and their Relation to the Organisation of the 

 Individual. 



By J. Bretland Farmer, D.Sc., F.K.S. 



(Received May 13, — Lecture delivered April 25, 1907.) 



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 Her twig, 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. 



Whilst I do not of course pretend that all these questions can be 

 satisfactorily answered at present, so many new facts which bear upon them 

 have come to light within recent times that I venture to indicate some of 

 what I conceive to be the more important results that have been obtained. 



Every animal and plant either consists of a single cell, or it is made up of 

 a cell-colony the members of which have had a common origin, inasmuch as 

 they have all sprung from one mother-cell, the egg. And it is in the cells 

 that the properties of an individual must ultimately be sought. 



The more closely the cell is studied, the more irresistibly are we compelled 

 to admit the supreme importance of the nucleus in directing and controlling 

 its metabolic activities. Experiments have abundantly proved that if a 

 nucleated protoplasmic mass be divided by artificial means, so that one 



