man, who
combines in his physical nature all the perfections of the animal, and
who is the end of all this long progression of organized beings.'
Agassiz recognizes man alone as cosmopolite; and Comte regards him as
the supreme head of the economy of nature, and representative of the
fundamental unity of the anatomical scale.

But another and more obvious example of unitization in complexity, is
derivable from the consideration of the animal organism, and will soon
be given.

We will merely mention in passing, that the most complex animals, in the
various stages of fetal development through which they pass, correspond
to the types of structure which are permanent in the lower forms of
animal life. Thus, in the zoological chain, there are beings of all
grades, from the most simple in structure to the most complex; and the
most complex animal, in its development from the ovum or egg, passes
through all these grades of structure, ending in that which is above
all, and distinctively its own. 'Without going into tedious details, man
presents, as regards the most important of his constituent structures,
his nervous system, the successive characteristics of an avertebrated
animal, a fish, a turtle, a bird, a quadruped, a quadrumanous animal,
before he assumes the special human characteristics.' (Draper.)

Our purpose being to show that while complexity of structure is
constantly increasing, unitization, or the organized dependence of one
part on another, is, at the same time, becoming more complete, we shall
refer briefly to the comparative anatomy and physiology of animals.
There is in this connection such wealth of material--a long chain of
animal beings with all grades of structure from very simple to very
complex; each complex animal, in its development from the ovum, passing
through all the lower types of structure in succession; so many new
organs and functions arising in the course of this development; each
organ so arising, becoming, in its turn, more complex in structure, more
specialized in function, and more dependent on the office of other
organs;--in the midst, I say, of all this wealth of material, indicated
here in a great general and imperfect manner, the difficulty, in so
brief an exposition as this, is to know what facts to seize upon as
calculated to illustrate most aptly the principle under consideration.

The development of the senses, with reference to their organs, nerves,
and functions, presents a s