GENERAL SUMMARY.

103

which insures the perpetuity of form, at least for a long time, while the other insures its mutation. Of these two great causes, one is the instinct which secures the preservation of the species, viz., that of reproduction and the other is the instinct which secures the preservation of the individual, viz., hunger.

So said Schiller long ago:

Einstweilen bis den Bau der Welt;
Philosophie zusammenhält,

Erhält sich ihr Getriebe,

Durch Hunger und durch Liebe.

Which I have ventured to translate very liberally:

"Until the earth is all explained,
Without call on power above,

Its workings still will be sustained
By Hunger and by Love."

I present you, thus, in this series of lectures, the barest outlines of the state of existing knowledge concerning the origin and evolution of life, as explained by natural causes. We have considered the subject from the standpoints of paleontology, comparative anatomy, and natural selection only. Of these fields, we have had time to take only bird's-eye views. The proofs offered by philology, the study of languages, and chorography, the geographical distribution of animals, are no less clear and convincing. But these studies are entirely out of our special province. I refer you to the now familiar works of Mr. Darwin, of Mr. Wallacewhose discoveries really forced upon Mr. Darwin the publication of his own views, prematurely, as he then believed— of Haeckel, Schleicher, Geiger, Steinthal, and the recent epitome by Oscar Schmidt, for a full and complete statement of all the evidence. Evidence which may now be likened to an arch composed of many pieces, with palæon

104

GENERAL SUMMARY.

tology and comparative anatomy as foundation stones at either end, and natural selection as the key-stone in its center.

I do not know how I may better close this part of our subject, now, than by repeating, with very slight modification, the recapitulation of Mr. Darwin at the close of his first and greatest work, the "Origin of Species." It is to his genius that we owe the whole elaboration and proof of the "Theory of Descent," as first advanced by Lamarck in 1809, as it is to his marvelous collection of facts, his clearness of statement, and his candor, that is due its general adoption in every field of science to-day :

It is interesting to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing in the bushes, insects flitting among the flowers, and worms crawling upon the bosom of the great mother earth. It is interesting to contemplate all these things, and to reflect that these elaborately constructed forms, so different from each other, yet so dependent upon each other, have all been produced by laws continually acting around us. The laws of growth and reproduction; a ratio of increase so high as to lead to a struggle for life, as a consequence to natural selection, and the slow but certain improvement of forms. Thus, from the war of nature, from famine, and from death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly and inevitably follows. There is a grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms, or into one; and in that, whilst this planet has gone cycling on, according to a fixed law of gravity-from so simple a beginning-endless forms, most beautiful, most varied, and most wonderful, have been, and are being evolved.

Fig. 9.-The
Amœba.
(p. 114)

seg

b, subdivided

a typical cell. a, cell Fig. 11.-Seg- Fig. 12.-Furth- Fig. 13.-Continuing
wall. b, cell contents mentation of er process of segmentation. a, cell
or protoplasm. c, nu- the cell. a, cell mentation. a, cell wall.
cleus and nucleolus. wall. b, subdi- wall. b, subdivid- cells.
(pp. 109-113)

vided cell showing division of nucleolus. (p. 144)

ed cells, the low

est of which shows a subdivided nucleus.

Fig. 18.-The impregnated ovum. a, zona pellucida (wall). b, sperm nucleus. c, nucleus of the ovum. (p. 125)

Fig. 19.-The impregnated Fig. 20.-The ovum at full ovum. a, the nucleus result- maturity. a, the micropole. b, ing from the fusion of the the zona pellucida (wall) showsperm and germ nucleus. b, ing the pore canals (stria). C, the cell wall. (p. 125) the seminal cord, d, the germinal vesicle (nucleus of the ovum). (p. 125)

THE CELL AND ITS REPRODUCTION.

PROTOPLASM AND ITS PROPERTIES.

105

LECTURE VI.

PROTOPLASM AND ITS PROPERTIES.

CONTENTS.

The History of Histology-The Invention and Use of the Microscope -The Discovery and Doctrine of The Cell-Derivation and Import of The Cell-The Cell Wall-The Nucleus and Nucleolus-The Cell Contents or Protoplasm-The Amœba-The Properties of Protoplasm-Motion-The Color Changes of the Chameleon-Ciliary Motion-Motion of Other Cells-Molecular Motion-Molecular Changes in the Ovum-Parthenogenesis-Motion as the Essence of Reproduction

We have already seen that different machinery or apparatus is required to effect the various changes of matter and force. We convert chemical force or affinity into galvanism in galvanic cups, magnetism into electricity with iron bars and wires, heat into motion with boilers, cylinders and pistons, etc. That physical may be converted into physiological force there is requisite animal or vegetable matter. In our day, we name this matter or apparatus protoplasm. In complicated arrangement we say the protoplasm constitutes an organism. In the study of physiology we are engaged with the construction of the organism (instrument) which sets the force free, with the mode of action by which it is changed to other forms, and with the various forms under which it reappears.

As there can be no force without matter, there can be no knowledge of action without knowledge of construction. Our knowledge of the

Construction of the Body

from an historical standpoint naturally falls under two