Chap. IV.] NATUKAL SELECTION. 



105 



to 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 unex- 

 pected nature, will ensue. 



As we see that those variations which,' under domes- 

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

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

 stance, 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 chickens; in the horns of our sheep 

 and cattle when nearly adult; — so in a state of nature"^ 

 natural selection will be enabled to act on and modify 

 organic beings at any age, by the accumulation of varia- 

 tions 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 modifications may affect, 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 be- 

 come extinct. 



Natural selection will modify the structure of the 



