spheroidal
yelk-sac and a discoidal--sometimes partially lobed--placenta. So that
it is only quite in the later stages of development that the young human
being presents marked differences from the young ape, while the latter
departs as much from the dog in its development, as the man does.

Startling as the last assertion may appear to be, it is demonstrably
true, and it alone appears to me sufficient to place beyond all doubt
the structural unity of man with the rest of the animal world, and more
particularly and closely with the apes.

Thus, identical in the physical processes by which he
originates--identical in the early stages of his formation--identical in
the mode of his nutrition before and after birth, with the animals which
lie immediately below him in the scale--Man, if his adult and perfect
structure be compared with theirs, exhibits, as might be expected, a
marvellous likeness of organization. He resembles them as they resemble
one another--he differs from them as they differ from one another.--And,
though these differences and resemblances cannot be weighed and
measured, their value may be readily estimated; the scale or standard
of judgment, touching that value, being afforded and expressed by the
system of classification of animals now current among zoologists.

A careful study of the resemblances and differences presented by
animals has, in fact, led naturalists to arrange them into groups, or
assemblages, all the members of each group presenting a certain amount
of definable resemblance, and the number of points of similarity being
smaller as the group is larger and 'vice versa'. Thus, all creatures
which agree only in presenting the few distinctive marks of animality
form the 'Kingdom' ANIMALIA. The numerous animals which agree only in
possessing the special characters of Vertebrates form one 'Sub-Kingdom'
of this Kingdom. Then the Sub-kingdom VERTEBRATA is subdivided into the
five 'Classes,' Fishes, Amphibians, Reptiles, Birds, and Mammals, and
these into smaller groups called 'Orders'; these into 'Families'
and 'Genera'; while the last are finally broken up into the smallest
assemblages, which are distinguished by the possession of constant,
not-sexual, characters. These ultimate groups are Species.

Every year tends to bring about a greater uniformity of opinion
throughout the zoological world as to the limits and characters of these
groups, great and small. At present, for example, no one has