THE ORIGIN OF LIFE 77 



to be observed that though the vertebrate eye is on 

 the same general plan with that of the higher 

 molluscs, it differs in some very important details. 

 These vertebrate eyes appeared with the fishes in the 

 Silurian, and I have shown from the structure of an 

 unusually well-preserved eye of a Lower Carboniferous 

 fish (Palaoniscus) that in the Palaeozoic some of the 

 most minute and delicate arrangements of the eye of the 

 fish already existed. 1 Thus the origin of such organs 

 as the eye becomes as inexplicable on the principle 

 of spontaneous evolution as that of the animal itself. 



But while we cannot explain how eyes may be 



acquired, we know something as to the causes of 



their being lost, which may perhaps throw light on 



their origin. A remarkable illustration of this, and 



also of transmutation as distinguished from origin, 



and of the equivocal value of the term species as 



used by evolutionists, is furnished by the cave 



animals of the great caverns of Kentucky and 



Virginia, recently so ably described by Packard. 2 



These creatures are acknowledged to be merely 



varietal forms, which by virtue of living for many 



generations, or it would appear sometimes in a few 



generations, in the darkness of caverns, have lost the 



power of vision, and even dispense with eyes, while 



they have been modified in other respects, as, for 



example, in the better development of their organs 



1 Acadian Geology, Supplement, p. 101. 



2 Cave Fauna, Memoirs National Academy of Sciences (U.S.A.), 

 vol. iv. 



