The adult
dentition is preceded by a widely different milk dentition. Any one may,
of course, deny that the teeth in either case have been adapted for tearing
flesh, through the natural selection of successive variations; but if this
be admitted in the one case, it is unintelligible to me that it should be
denied in the other. I am glad to find that so high an authority as
Professor Flower has come to this same conclusion.
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. The end gained is the same, but the means,
though appearing superficially to be the same, are essentially different.
The principle formerly alluded to under the term of ANALOGICAL VARIATION
has probably in these cases often come into play; that is, the members of
the same class, although only distantly allied, have inherited so much in
common in their constitution, that they are apt to vary under similar
exciting causes in a similar manner; and this would obviously aid in the
acquirement through natural selection of parts or organs, strikingly like
each other, independently of their direct inheritance from a common
progenitor.
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