The extraordinary cases given in a former chapter, of widely different fishes possessing electric organs--of widely different insects possessing luminous organs--and of orchids and asclepiads having pollen-masses with viscid discs, come under this same head of analogical resemblances.

But these cases are so wonderful that they were introduced as difficulties or objections to our theory.

In all such cases some fundamental difference in the growth or development of the parts, and generally in their matured structure, can be detected.