704 THE AMERICAN NATURALIST. 
not original. Were we permitted to suppose that the lungs 
had never existed in these species, we might then assume 
that the low grade of respiration required by the animals was 
taken on by the integument and buccal cavity when the gills 
disappeared, so easily that there was no particular demand for 
the production of lungs. But that Zungs already present should 
be lost by an air-breathing animal, and should be retained by a 
closely related water-living animal, is remarkable. 
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