SECTIONAL TRANSACTIONS.— C. 356 



Dr. F. A. Bather, F.R.S. : — 



The question posed. Can characters be regarded as 

 independent, i.e. as manifestations of independent factors in 

 the germ ? Does evolution take place solely by addition or 

 loss of such factors ? Is there not also a gradual modification 

 of the body, resulting in a continuous transition ? Palaeonto- 

 logists find such transition to be the rule in those cases where 

 the geological record is sufficiently complete. (See President's 

 Address, Section C, heading ' Continuity in Development.') 

 Palaeontologists support the theory of Recapitulation, and 

 believe that, in many cases, gradual modification of the 

 adult and senile body is, in the course of race-history, pushed 

 back to earlier growth -stages. (See President's Address, 

 Section C, heading 'Recapitulation.') Can such cases be 

 explained by independent factors in the germ ? Does not 

 that hypothesis involve, first, an alteration of the germ 

 through change in the body ; secondly, the determination of 

 that germinal change in a direction harmonious with bodily 

 change ? 



Dr. E. EuGGLES Gates: — 



According to miitationiet hypothesis, germinal characters 

 arise as alterations of single elements of the germ plasm. 

 This conception avoids the difficulties involved in considering 

 the change as due to the loss or addition of a factor. It 

 recognises on the one hand the solidarity of the germ plasm as 

 a whole, and on the other the independent origin of variations 

 in its several parts. Such variations are termed karyogenetic, 

 since they apparently arise in the nuclei and are perpetuated 

 by mitotic division. Mutations of this nature are almost 

 universal amongst wild plants and animals, and some of 

 them are so small that for general purposes they are practi- 

 cally continuous. They differ from the Darwinian conception 

 of continuous variation, however, in that (i.) they do not 

 arise in any regular order, (ii.) they are inherited as separate 

 units. But Recapitulation is an almost equally widespread 

 phenomenon in animals, and to a less extent in plants. The 

 recapitulation in animal embryos, and in such fossil groups 

 as the Ammonites, implies the addition of terminal stages to 

 the development of the organism. From the standpoint of 

 organic structure this process is clearly different from a 

 mutation by which the nuclear unit is modified throughout 

 the organism. Recapitulatory characters thus fall into two 

 groups : (i.) embryonic, which appear always to imply adap- 

 tation of the organism to different conditions, and are best 

 explained bj' the neo-Lamarckian principle; (ii.) orthogenetic. 

 which appear late in the life-cycle but are germinal in origin 

 and non-adaptational. 



Prof. J. E. Duerden. — MendeVtsm ; Paleontology; 

 Evolution. 



Recent investigations in genetics in general give support 

 to the factorial hypothesis, namely, that the characteristics 

 of the body are repre.sented in the germ plasm, in all proba- 

 bility in association with the chromosomes. Supporting 

 evidence is foi-thcoming from sex. crossing-over and localisa- 

 tion. Any hereditary change in an organism must therefore 

 be associated with factorial change in the germ plasm. 

 Casual mutations readily admit of ^Mendelian interpretation, 

 but evolution in general does not take place by changes of 

 this kind. Evolution of species often seems to call for a 

 similar change in the whole assemblage of individuals within 

 an area, while palaeontology and the study of numbers of 



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