es,
which hang down from the palate along each side of the mouth. They thus
form two longitudinal series, each plate of which is placed transversely to
the long axis of the body, and all are very close together. On depressing
the lower lip the free outer edges of these plates come into view. Their
inner edges are furnished with numerous coarse hair-like processes,
consisting of some of the constituent fibres of the horny plates--which, as
it were, fray out--and the mouth is thus lined, except below, by a network
of countless fibres formed by the inner edges of the two series of plates.
This network acts as a sort of sieve. When the whale feeds it takes {41}
into its mouth a great gulp of water, which it drives out again through the
intervals of the horny plates of baleen, the fluid thus traversing the
sieve of horny fibres, which retains the minute creatures on which these
marine monsters subsist. Now it is obvious, that if this baleen had once
attained such a size and development as to be at all useful, then its
preservation and augmentation within serviceable limits, would be promoted
by "Natural Selection" alone. But how to obtain the beginning of such
useful development? There are indeed certain animals of exclusively aquatic
habits (the dugong and manatee) which also possess more or less horn on the
palate, and at first sight this might be taken as a mitigation of the
difficulty; but it is not so, and the fact does not help us one step
further along the road: for, in the first place, these latter animals
differ so importantly in structure from whales and porpoises that they form
an altogether distinct order, and cannot be thought to approximate to the
whale's progenitors. They are vegetarians, the whales feed on animals; the
former never have the ribs articulated in the mode in which they are in
some of the latter; the former have pectoral mammae, and the latter are {42}
provided with two inguinal mammary glands, and have the nostrils enlarged
into blowers, which the former have not. The former thus constitute the
order Sirenia, while the latter belong to the Cetacea. In the second place,
the horny matter on the palates of the dugong and manatee has not, even
initially, that "strainer" action, which is the characteristic function of
the Cetacean "baleen."

[Illustration: FOUR PLATES OF BALEEN SEEN OBLIQUELY FROM WITHIN.]

[Illustration: DUGONG.]

There is another very curious structure, the origin or the disapp