SECTIONAL TRANSACTIONS.—!). 367 



some sensations have an " all-or-none ' character — that is to saj-, if tliey are evoked 

 at all, their intensity is independent of the strength of the stimulus — whereas other 

 sensations are graded. One basis for such gradation appears to be the integration 

 •of pairs of antagonistic sensory apparatus in such a way that activity of the one 

 involves simultaneously inhibition of the other, and that all grades of such duplex- 

 balanced responses are possible according to the strength, &c., of the stimulus. Xhis 

 arrangement is also responsible for the phenomenon of contrast and adaptation. 



Wherever there would otherwise occur incompatible, antagonistic mental pro- 

 cesses, inhibition steps in and represses one of them. The appearance in consciousness 

 of an idea depends largely on its congruity with the total mental attitude. Mental 

 acts are generally set in a matrix of more persistent mental attitudes — ' fields ' of 

 attention, &c., with which they are compatible. The revival of a forgotten idea 

 may be impossible owing to the unfavourable ' constellation ' which obtains at the 

 moment. Such lack of incongruity between different systems, or between any given 

 system and the whole of which it forms a part, is a notion employable m the problems 

 of heredity. 



During the development, and, indeed, throughout the life of the individual, well- 

 marked changes may occur in its personality or in one or more of the mental qualities 

 which go to compose it. Sometimes the character of the individual suddenly under- 

 goes a complete change, as in cases of multiple personality. These phenomena, when 

 considered from the standpoint of heredity, suggest that the individual actually 

 inherits a vast number of mutually antagonistic characters, and that tlicir actual 

 appearance in the course of the life of the individual depends on what has been 

 variously termed above internal configuration, constellation, and on such external 

 influences as education and environment. 



(See, further, p. 390.) 



Tuesday, August lOi 



22. Prof. Julian Huxley. — Lecture on the Study of Growth and its bearings 

 upon Morphology and Evolution. 



The study of the relative growth of parts of the body has many points of interest, 

 both in itself and in its bearings on classification, evolution, and other subjects. The 

 growth of most irgans is roughly in direct linear proportion to the growth of the body 

 as a whole. "! lere are, however, many organs which grow disproportionately, or, to 

 use Champy's term, heterogonicaUy. Excellent examples of tliis are found in many 

 Crustacea, e.g. the abdomen in female shore-crabs (Carcinus), or the large chela in male 

 fiddler-crabs (Uca). Analysis shows that these grov,' according to the formula y=6.r'-, 

 where (/=organ weight, .r=weight of rest of body, and b and k are constants. This 

 might have been prophesied a priori as the simplest formula for heterogenic growth, 

 as it merely implies that the ratio for the growth-rates of organ and body remains 

 constant throughout life. 



In the above cases both sexes are alike at the opening of post-larval existence, and 

 the differential growth continues till death. As a result neither the female Carcinus 

 nor the male Uca has any fixed morphological proportions, since the relative size of 

 the abdomen, or chela, is a function of absolute body-size. 



Similar facts are found in other Crustacea, but the heterogeny may only start at 

 sexual maturity (chela of (J Maia). 



A further point is that even within the heterogenic organ growth is not uniform . 

 In chelae the tip is growing faster than the base, the base faster than the body. The 

 excessive growth of the chelaj also induces slight overgrowth of neighbouring parts. 

 The facts can be brought into relation with Cliild's physiological gradients. 



In many insects similar relations are found for various organs, e.g. tlio mandibles 

 of stag-beetles (Lucanidm) and the ' horns ' of dynastida. Here, since the organs 

 only appear at the imaginal stage, we must postulate the formation at a heterogonic 

 rate of some substance which determines the size of these organs. 



A peculiarly interesting case is found in ants with polymorphic neuters. In some 

 species all gradations are found, from small workers to large soldiers, and in these 

 the head-weight bears the same relation to body -weight as does the chela of Uca, &c. 

 This indicates that in all probability the different forms are not genetically different, 

 but have merely had their larval development stopped at different absolute sizes. 



Another interesting case of differential growth is afforded by the antlers of deer. 

 In red deer, in spite of tlie fact that antlors are shed every year, the same average 



