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cave inhabitants is that most of them are blind, and as might be 
expected from their living in total darkness, without colour. But 
they are not all blind. In the same water with the blind fish, 
there is another form, nearly allied to them but quite a distinet 
genus, which has simall black eyes, and its body of a dark colour. 
Here is a puzzle not easily explained. Darvwin’s view seems to 
be that the blind forms have been longer in the caves than those 
still retaining vision. ‘There seems, according to one observer, to 
have been a succession: “animals not far remote from ordinary 
forms preparing the transition from light to darkness. Next 
follow those that are constructed for twilight; and, last of all, 
those destined for total darkness.” The blind fish, which, except 
as regards loss of sight, differ in no respect from the same species 
living at this day in the Green river outside the cave, are supposed, 
on geological evidences which cannot be entered into here, to 
have been in the cave ever since the beginning of the quaternary 
or postpliocene era, if not earlier. Darwin remarks that “by the 
time an animal had reached, after numberless generations, the 
deepest recesses, disuse will on the above view have more or less 
perfectly obliterated its eyes, and natural selection will often 
have effected other changes, such as an increase in the length of 
the antenne or palpi, as a compensation for blindness.” This 
last remark of course refers to crustacea and insects. But the 
extreme sensitiveness of all the outer integuments and acute sense of 
hearing of the blind fish, as a compensation for thei blindness, is. a 
remarkable fact which an eye-witness has testified. They are 
sensible of the slightest tremor or movement of the water, and 
feeding on other fish and crustacea they know exactly where 
their prey is, and at what distance, chasing and securing them 
with as much ease and certainty as if their eyes were perfect, 
Taking the facts as a whole, they lead to the belief that most 
of these cave animals may have been derived from other species 
thst had migrated into the cave. ages back, from the outer 
world—the changes of structure adapting them to a cave life being 
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