86 NATURAL SELECTION. Chap. IV. 



the good of the being, will cause other modifications, 

 often of the most unexpected nature. 



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 in- 

 stance, in the seeds of the many varieties of our culinary 

 and agricultural plants; in the caterpillar and cocoon 

 stages of the varieties of the silkworm ; 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 profitable variations at that age, and by 

 their inheritance at a corresponding age. If it profit a 

 plant to have its seeds more and more widely dissemi- 

 nated 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. These modifications 

 will no doubt affect, through the laws of correlation, the 

 structure of the adult ; and probably in the case of those 

 insects which live only for a few hours, and which never 

 feed, a large part of their structure is merely the cor- 

 related result of successive changes in the structure of 

 their larvse. So, conversely, modifications in the adult 

 will probably often affect the structure of the larva ; but 

 in all cases natural selection will ensure that modifica- 

 tions consequent on other modifications at a different 

 period of life, shall not be in the least degree injurious : 

 for if they became so, they would cause the extinction 

 of the species. 



Natural selection will modify the structure of the 



