spotted in lines; and stripes can be plainly distinguished in the whelp
of the lion. We occasionally though rarely see something of this kind
in plants: thus the embryonic leaves of the ulex or furze, and the
first leaves of the phyllodineous acaceas, are pinnate or divided like
the ordinary leaves of the leguminos .
The points of structure, in which the embryos of widely different
animals of the same class resemble each other, often have no direct
relation to their conditions
of existence. We cannot, for instance, suppose that in the embryos of
the vertebrata the peculiar loop-like course of the arteries near the
branchial slits are related to similar conditions, in the young mammal
which is nourished in the womb of its mother, in the egg of the bird
which is hatched in a nest, and in the spawn of a frog under water. We
have no more reason to believe in such a relation, than we have to
believe that the same bones in the hand of a man, wing of a bat, and
fin of a porpoise, are related to similar conditions of life. No one
will suppose that the stripes on the whelp of a lion, or the spots on
the young blackbird, are of any use to these animals, or are related to
the conditions to which they are exposed.
The case, however, is different when an animal during any part of its
embryonic career is active, and has to provide for itself. The period
of activity may come on earlier or later in life; but whenever it comes
on, the adaptation of the larva to its conditions of life is just as
perfect and as beautiful as in the adult animal. From such special
adaptations, the similarity of the larv or active embryos of allied
animals is sometimes much obscured; and cases could be given of the
larv of two species, or of two groups of species, differing quite as
much, or even more, from each other than do their adult parents. In
most cases, however, the larv , though active, still obey more or less
closely the law of common embryonic resemblance. Cirripedes afford a
good instance of this: even the illustrious Cuvier did not perceive
that a barnacle was, as it certainly is, a crustacean; but a glance at
the larva shows this to be the case in an unmistakeable manner. So
again the two main divisions of cirripedes, the pedunculated and
sessile, which differ widely in external appearance, have larv in all
their several stages barely distinguishable.
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