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 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 dissemi¬ 
nated by the wind, I can see no greater diJfficulty in this 
being eifected 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 
Avill 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 larva). 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 
