, Cetacea (whales) and Edentata (armadilloes, scaly ant-eaters, etc.),
are likewise on the whole the most abnormal in their teeth, but there are
so many exceptions to this rule, as Mr. Mivart has remarked, that it has
little value.
I know of no case better adapted to show the importance of the laws of
correlation and variation, independently of utility, and therefore of
natural selection, than that of the difference between the outer and inner
flowers in some Compositous and Umbelliferous plants. Everyone is familiar
with the difference between the ray and central florets of, for instance,
the daisy, and this difference is often accompanied with the partial or
complete abortion of the reproductive organs. But in some of these plants
the seeds also differ in shape and sculpture. These differences have
sometimes been attributed to the pressure of the involucra on the florets,
or to their mutual pressure, and the shape of the seeds in the ray-florets
of some Compositae countenances this idea; but with the Umbelliferae it is
by no means, as Dr. Hooker informs me, the species with the densest heads
which most frequently differ in their inner and outer flowers. It might
have been thought that the development of the ray-petals, by drawing
nourishment from the reproductive organs causes their abortion; but this
can hardly be the sole case, for in some Compositae the seeds of the outer
and inner florets differ, without any difference in the corolla.
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