ed certain Pachyderms in the same
sub-order with ruminants; for example, he dissolves by gradations the
apparently wide interval between the pig and the camel. The Ungulata
or hoofed quadrupeds are now divided into the even-toed or odd-toed
divisions; but the Macrauchenia of South America connects to a certain
extent these two grand divisions. No one will deny that the Hipparion
is intermediate between the existing horse and certain other ungulate
forms. What a wonderful connecting link in the chain of mammals is the
Typotherium from South America, as the name given to it by Professor
Gervais expresses, and which cannot be placed in any existing order. The
Sirenia form a very distinct group of the mammals, and one of the most
remarkable peculiarities in existing dugong and lamentin is the entire
absence of hind limbs, without even a rudiment being left; but the
extinct Halitherium had, according to Professor Flower, an ossified
thigh-bone "articulated to a well-defined acetabulum in the pelvis," and
it thus makes some approach to ordinary hoofed quadrupeds, to which the
Sirenia are in other respects allied. The cetaceans or whales are
widely different from all other mammals, but the tertiary Zeuglodon and
Squalodon, which have been placed by some naturalists in an order
by themselves, are considered by Professor Huxley to be undoubtedly
cetaceans, "and to constitute connecting links with the aquatic
carnivora."

Even the wide interval between birds and reptiles has been shown by
the naturalist just quoted to be partially bridged over in the
most unexpected manner, on the one hand, by the ostrich and extinct
Archeopteryx, and on the other hand by the Compsognathus, one of
the Dinosaurians--that group which includes the most gigantic of all
terrestrial reptiles. Turning to the Invertebrata, Barrande asserts, a
higher authority could not be named, that he is every day taught that,
although palaeozoic animals can certainly be classed under existing
groups, yet that at this ancient period the groups were not so
distinctly separated from each other as they now are.

Some writers have objected to any extinct species, or group of species,
being considered as intermediate between any two living species, or
groups of species. If by this term it is meant that an extinct form is
directly intermediate in all its characters between two living forms or
groups, the objection is probably valid. But in a natural classification
many fos