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as ‘ eye-like organs ? 9 Are they to be compared to those 
which are found in the head of the Fish, or are they only of 
the same simple origin as the eyes of the Invertebrata ? This 
question does not seem to have been fully treated of by Dr. 
TTssow. If they are only to be compared to those eyes or eye- 
like organs of which we have already spoken as existing in 
Polyophthalmns, the question not unnaturally arises, may they 
not have some other function? may it not be that their re- 
semblance, such as it is, to the ordinary eye, is only another j 
illustration of that instructive and frequently recurring phe- 
nomenon that, under somewhat similar conditions, parts of |j 
animals, or, indeed, animals themselves, though of the most 
diverse origin, come to have very similar appearances in their j 
adult condition ? The uninstructed naturalist finds it difficult 
to believe that the wing of a bird and of a bat are formed on 
totally different structural arrangements ; some Crustacea look 
more like bivalves than Crayfishes ; and the remarkable out- 
