ay successfully take on the function of feeding, moving, or
reproducing apparatus. In the highest, on the contrary, a great number
of parts combine to perform each function, each part doing its allotted
share of the work with great accuracy and efficiency, but being useless
for any other purpose.

On the other hand, notwithstanding all the fundamental resemblances
which exist between the powers of the protoplasm in plants and in
animals, they present a striking difference (to which I shall advert
more at length presently), in the fact that plants can manufacture fresh
protoplasm out of mineral compounds, whereas animals are obliged to
procure it ready made, and hence, in the long run, depend upon plants.
Upon what condition this difference in the powers of the two great
divisions of the world of life depends, nothing is at present known.

With such qualifications as arises [98] out of the last-mentioned
fact, it may be truly said that the acts of all living things are
fundamentally one. Is any such unity predicable of their forms? Let us
seek in easily verified facts for a reply to this question. If a drop
of blood be drawn by pricking one's finger, and viewed with proper
precautions, and under a sufficiently high microscopic power, there will
be seen, among the innumerable multitude of little, circular, discoidal
bodies, or corpuscles, which float in it and give it its colour, a
comparatively small number of colourless corpuscles, of somewhat larger
size and very irregular shape. If the drop of blood be kept at the
temperature of the body, these colourless corpuscles will be seen to
exhibit a marvellous activity, changing their forms with great rapidity,
drawing in and thrusting out prolongations of their substance, and
creeping about as if they were independent organisms.

The substance which is thus active is a mass of protoplasm, and its
activity differs in detail, rather than in principle, from that of the
protoplasm of the nettle. Under sundry circumstances the corpuscle dies
and becomes distended into a round mass, in the midst of which is seen
a smaller spherical body, which existed, but was more or less hidden,
in the living corpuscle, and is called its nucleus. Corpuscles of
essentially similar structure are to be found in the skin, in the lining
of the mouth, and scattered through the whole framework of the body.
Nay, more; in the earliest condition of the human organism, in that
state in which it has but j