52 HEREDITY AND SELECTION IN SOCIOLOGY 



plasm to one-half their original number. According as chance 

 brings together, in amphimixis, two cells containing a majority 

 or a minority of the ids A, will the embryonic cells, and conse- 

 quently the cells in the growing organism, have a tendency to 

 a plus or to a minus variation. Any germ-cell which contains 

 a majority of plus determinants may unite with another cell 

 containing likewise a majority of plus determinants, and the 

 character represented by these determinants wiU be the more 

 strongly accentuated in the ofispring. 



When a given characteristic becomes of pronounced utihty to 

 the Ufe of the species, the determinants of that characteristic 

 will be more likely to vary in an ascendant than in a regressive 

 direction. For instance, the peculiar luminous apparatus 

 developed by fishes inhabiting the dark depths of the ocean is 

 obviously adapted to their conditions of life. Some of them 

 possess rows of miniature organs with luminous secretion on 

 their sides or along their ventral surface ; others possess similar 

 organs on the head ; and it is extremely probable that these 

 luminous organs serve to attract the smaU animals which form 

 the prey of these fishes, just as the electric light above groimd 

 attracts insects, which are lured by it to their destruction. "When 

 such luminous organs became directly useful to the species, 

 they were bound to increase, for those individuals whose deter- 

 minants tended to a plus variation of these organs would ob- 

 viously be favoured in the struggle for existence ; amphimixis 

 would tend to disseminate the determinants favourable to this 

 new adaptation, and ultimately the possessing of luminous 

 organs would become a characteristic of the species. 



Natural selection operates only when the variations efiected 

 in the germ-plasm by perturbations in the balance of intra- 

 germinal nutrition attain selective value — that is to say, when 

 they become of vital importance for the species in the struggle 

 for fife. If advantageous, natural selection will further the 

 development of such variations by eliminating gradually and 



