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to his theory ; but now that I understand it more correctly, I see 
that this difficulty can be got over by referring the two (as diverg- 
ing descendants) to some common ancestor, not eyeless, who may 
have lived where the Atlantic Ocean now rolls, at some distant 
period when America and Europe were united. Therefore, the fact 
has not the significance I supposed. A Trechus may have wan- 
dered into each of these caves, and by process of natural selection, 
after frequent variation into all manner of other forms, which being 
unsuitable have not been preserved, have at last hit upon the form of 
an Anophthalmus. But if he thus saves his theory, what becomes 
of his disbelief in the effects of physical condition % If it has no effect, 
why have they all turned into Anophthalmi ? The only explication 
which I can imagine for him is, that in every cave Trechi entered, 
and in each and all threw off descendants of all different kinds, as 
well as Anophthahni , none of which were suited to the physical con- 
dition except the Anophthahni, and therefore the latter alone sur- 
vived. Whether this is a more philosophical explanation of their 
presence than the view that their production was influenced by the 
physical condition of the place, I leave to the reader to determine. 
I shall only follow Mr Darwin for a few lines farther in his re- 
marks on this subject. He says, u On my view, we must suppose 
that American animals having ordinary power of vision slowly 
migrated by successive generations from the outer world into the 
deeper and deeper recesses of the Kentucky Caves, as did European 
animals into the caves of Europe. We have had some evidence of 
this gradation of habit ; for, as Schiodfce remarks, £ animals not far 
remote from ordinary forms prepare the transition from light to 
darkness. Next follow those that are constructed for twilight ; and 
last of all, those destined for total darkness . 5 55 If Darwin reads this 
as meaning that there is a gradation in form and affinity between 
the animals which are found at the entrance, and those found in total 
darkness, he is in error — there is none. It is the gradation in adap- 
tation to darkness that Schiodte is speaking of. Those at the 
entrance, with small eyes, belong to the Pristonychi , large black 
beetles found in cellars and such places. The Anophthahni belong 
to the small Trechidce , of which there are none specially found at 
the entrance. 
I might take other exception to the facts adduced by Mr Dar- 
win, or to his application of them. For instance, he says of the 
