XXIII ANIMAL MIGRATIONS 383 
€nces, and there were no animals to aid in their 
reproduction, to feed upon them, to dispose of their 
dead carcasses, etc., the dominant forms would 
doubtless be quite different from what they are 
now. Darwin has shown by an admirable series of 
observations how necessary insect agency is to the 
fertilisation of the flowers of many plants. Hence 
the organs of those insects and the parts of the 
flowers have been (and are being) continually 
modified, or moulded, the one on the other. I can 
conceive that if certain Orchids were henceforth 
entirely freed from the visits of insects, their flowers, 
notwithstanding the apparent permanence of in- 
herited (though now useless) peculiarities, would 
immediately tend to revert to the symmetry which 
no doubt they possessed in the remote types. I 
have a good deal of evidence to show that in 
tropical countries many peculiarities of structure in 
the leaves and other parts of plants (prevailing 
through large suites of species and genera) have 
been brought about, and are still in part maintained, 
by the unremitting agency of insects, especially of 
Ants. These and many other matters require the 
fullest investigation before the precise relations of 
the changes, in animals and plants, that are taking 
place under our eyes, can be properly understood 
and appreciated. 
