268 PHYSIOLOGICAL DEVELOPMENT. 



posing the insects to have had the power of distinguishing 

 between colours. That Bees and Butterflies have this power 

 is manifest. They may be watched flying from flower to 

 flower, disregarding all other parts of the plants. And if 

 the less-specialized insects possessed some degree of such 

 discrimination, then the initial contrasts of colour above 

 described would be maintained and increased. Let such a 

 connexion be once established, and it must tend to become 

 more decided. Insects most able to discern the parts of 

 plants which afford what they seek, will be those most likely 

 to survive and leave offspring. Plants presenting most of 

 the desired food, and showing most clearly where it lies, will 

 have their fertilization and multiplication furthered in the 

 greatest degree. And so the mutual adaptation will become 

 ever closer; while it is rendered at the same time more 

 varied by the special requirements of the insects and of 

 the plants in each locality, under each change of con- 

 ditions. Of course, the genesis of the sweet 

 secretions and the odours of flowers, has a parallel interpre- 

 tation. The simultaneous production of honey, or some 

 kindred substance, is implied above; since, unless a bait 

 co-existed with the colour, the colour would not attract 

 insects, and would not be maintained and intensified by 

 natural selection. Gums, and resins, and balsams, are familiar 

 products of plants; apparently, in many cases, excreted as 

 useless matters from various parts of their surfaces. These 

 substances, admitting of wide variations in quality, as they 

 do, afford opportunities for the action of natural selection 

 wherever any of them, attractive to insects, happen to be 

 produced near the organs of fructification. And this action 

 of natural selection once set up, may lead to the establish- 

 ment of a local excretion, to the production of an excretion 

 more and more attractive, and to the disposal of the organ 

 containing it in such a way as most to facilitate the carry- 

 ing away of pollen. Similarly and simultaneously with 

 odours. Odours, like colours, draw insects to flowers. After 



