134 LOWER AMAZONS—PARA TO OBYDOS.  Cuap. VI. 
some scientific importance ; for they tend to show that a physiological 
species can be and is produced in nature out of the varieties of a pre- 

Transition forms between Heliconius Melpomene and H. Thelxiope. 
existing closely allied one. This is not an isolated case; for I observed, 
in the course of my travels, a number of similar instances. But in very 
