Chap. IV.] NATURAL SELECTION. 105 



judge, seem quite unimportant, we must not forget that 

 climate, food, &c, have no doubt produced some direct 

 effect. It is also necessary to bear in mind that, owing 

 to the law of correlation, when one part varies, and the 

 variations are accumulated through natural selection, 

 other modifications, often of the most unexpected nature, 

 will ensue. 



As we see that those variations which, under domesti- 

 cation, appear at any particular period of life, tend to 

 reappear in the offspring at the same period; — -for instance, 

 in the shape, size, and flavour of the seeds of the many 

 varieties of our culinary and agricultural plants ; in the 

 caterpillar and cocoon stages of the varieties of the silk- 

 worm; in the eggs of poultry, and in the colour of the down 

 of their chichens ; in the horns of our sheep and cattle 

 when nearly adult; — so in a state of nature natural selec- 

 tion will be enabled to act on and modify organic beings 

 at any age, by the accumulation of variations profitable 

 at that age, and by their inheritance at a corresponding 

 age. If it profit a plant to have its seeds more and more 

 widely disseminated by the wind, I can see no greater 

 difficulty in this being effected through natural selection, 

 than in the cotton-planter increasing and improving by 

 selection the down in the pods on his cotton- trees. 

 Natural selection may modify and adapt the larva of an 

 insect to a score of contingencies, wholly different from 

 those which concern the mature insect ; and these modifi- 

 cations may effect, through correlation, the structure of the 

 adult. So, conversely, modifications in the adult may 

 affect the structure of the larva ; but in all cases natural 

 selection will ensure that they shall not be injurious : 

 for if they were so, the species would become extinct. 



Natural selection will modify the structure of the 



