144 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
It is now many years ago since the editors of Silliman’s Journal 
requested the late Professor Agassiz to give them his opinion on the 
following question. In a certain dark subterranean cave, called the 
Mammoth Cave, there are found some peculiar species of blind fishes. 
Now the editors of Silliman’s Journal wished to know whether Profes- 
sor Agassiz would hold that these fish had been specially created in 
these caves, and purposely devoided of eyes which could never be of 
any use to them; or whether he would allow that these fish had prob- 
ably descended from other species, but, having got into the dark cave, 
gradually lost their eyes through disuse. Professor Agassiz, who was 
a believer in special creation, allowed that this ought to constitute 
a crucial test as between the two theories of special design and heredi- 
tary descent. “If physical circumstances,” he said, “ever modified 
organised human beings, it should be easily ascertained here.” And 
eventually he gave it as his opinion, that these fish “were created 
under the circumstances in which they now live, within the limits over 
which they now range, and with the structural peculiarities which now 
characterise them.” 
Since then a great deal of attention has been paid to the fauna of 
this Mammoth cave, and also to the faunas of other dark caverns, not 
only in the New, but also in the Old World. In the result, the 
following general facts have been fully established. 
1. Not only fish, but many representatives of other classes, have 
been found in dark caves. 
2. Wherever the caves are totally dark, all the animals are blind. 
3. If the animals live near enough to the entrance to receive some 
degree of light, they may have large and lustrous eyes. 
4. In all cases the species of blind animals are closely allied to 
species inhabiting the district where the caves occur; so that the 
blind species inhabiting the American caves are closely allied to 
American species, while those inhabiting European caves are closely 
allied to European species. 
5. In nearly all cases structural remnants of eyes admit of being 
detected, in various degrees of obsolescence. In the case of some of 
the crustaceans of the Mammoth cave the foot-stalks of the eyes are 
present, although the eyes themselves are entirely absent. 
Now, it is evident that all these general facts are in full agreement 
with the theory of evolution, while they offer serious difficulties to 
the theory of special creation. As Darwin remarks, it is hard to 
imagine conditions of life more similar than those furnished by deep 
