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Variation after Birth. L. H.

T. Piney Branch (D. C.)
Bailey......

17 Quarry Workshop and its
Variations in the Patellar Re-

plements..... ..........873, 976
flex as an Aid in Mental Winslow, G. M. Abstract of
Analysis. Prof. Witmer,

Heymons Segmentation of
Abstract of ...........

160 the Hexapod Body............
Varieties, Geographical........... 458 Witchell, C. A. Review of
Ternilla blakei...

1052 Rhoads' Mimetic Origin and
Vice-Presidents of the Amer-

Development of Bird-lan-
ican Association ........ 652

guage, and the Evolution
Vienna Propositions. R. Pound.

of Bird-song...
L'ipera berus....
413 Woodpeckers, Classification of

71
Vivipara, Sets of

694 Food Habits of..
Vivisection of Idiots.....

33
Woodsia alpina

751
Voglino, Dr. P ..........

528
mexicana .................

751
Vogt, C......

262 obtusa ............................. 751
Volcanic Activity in New Bruns-

oregona ............................. 751
wick......
401 scopulina ......

751
Volcanics in Maine......
394 Woodward, B. H....

88
in Michigan......

393 Woodworth, W. McM. Notes
Volcanic Rocks and Tuffs in

on Turbellaria .....

1046
Prussia.....

576 | Wright, G. F. Fresh Relics of
Vole (New) from Labrador...... 1051 Glacial Man Reported at
Von Gümbel, K...........

262 the Buffalo Meeting A. A.
Von Kupffer, K.
961 A. S.....

781
Pon Lenhossek, M.....

528 Wrinkling of Frog's Eggs Dur-
Von Norbeck, H. Ph....

613 ing Segmentation. C. B.
Von Sandberger, F....

439
Wilson

761
Von Wagner, F.....

528 XANTHIUM canadense
Von Zittel, K. A......

Xerophila leuitsis...... 287
Vuillemin, Dr. P

528

X-rays (illustrated).
Xyleborus dispar .......

319

pubescens.
Artificial Mutilations..... 837 Xyodesmus planus

415
Wagner, Dr. R........

612
Walcott, C. D.......

439 YUCATAN, Explorations in
Ward, H. M...
439

255
M....
88 Yung, E.....

263
Warren, H.C. Effects of Loss

937
of Sleep......

1061 Zeugites smilacifolia ....... 487
Fear Among Children .......

774 Zimmermann, Dr. A.........440, 962
The Nature of Feeding :

Zircon .....
Review of Halleck's Edu- Zoological News, 590, 758, 1052, 1046
cation of the Central Nery-

Zooology, 67, 143, 229, 323, 409,
ous System ......

1032

495, 590, 672, 752, 829, 943, 1046
Synæsthesia and Synopsia.. 689 Zoological News •
Washburn, F. L. A Case of

Mollusca

332
Renal Abnormality in a

Arthropoda.

285
Cat ........

331

Pisces ..... ..332, 412, 590, 1052
Wasps, Domestic Economy of.. 504

Reptilia....

......413, 1052
Water Pores.......

224
Aves...

-71, 591, 1052
Weiss, Dr. A....

Mammalia...

:72, 332, 1053
Weismann on Dimorphism in Zuber, R.......

962
Butterflies
Wernerite.........

813
Western subregion...

1017
Whitney, Josiah Dwight, Obit-
uary

868
Willey, F. E...
Wilson, C. B. Wrinkling of

Frog's Eggs during Seg-
mentation.

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WADE; W: Inheritance of

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The subject of this article is presented under the following sections :

I. The Formative Force of Organisms.
II. The Conception of Death.
III. A Comparison of Larva and Embryo.
IV. Concluding Remarks.

The first section is not new, but a reproduction without change, of an article published in Science, July 3d, 1885. As this article has not become generally known, and yet is an essential link in the chain of reasoning, I venture to repeat itThough written in 1885, I consider that to-day it is still sufficient to disprove Weismann's theory of germ plasm. Weismann has not considered this article, otherwise, from my point of view, he could not have maintained his theory.

This article is translated from one which appeared in the Biologisches Centralblatt, Vol. XV, Page 571, August 1st, 1895. A few trilling changes have been made in the text. An abstract of the article was read before the American Association for the Advancement of Science, at its recent Springfield meeting. ? Professor in the Harvard Medical School.

The views which I then defended have been recently brought forward in almost parallel form, and without essential additions, by 0. Hertwig (Zeit-und Streitfragen der Biologie, I, Heft, D. 32–53) as arguments against the views of Weis

mann.

The second section is also directed against Weismann, for it attempts to replace his conception of death by one more exact.

The third section is intended to make the significance of rejuvenation clear, and at the same time, by a comparison of larvæ and embryos, to demonstrate a law of heredity which has not been hitherto recognized.

THE FORMATIVE FORCE OF ORGANISMS.

The assertion is safe, that the majority of biologists incline at present to explain the forming of an organism out of its germ upon mechanical principles. The prevalent conception is that the forces of the ovum are so disposed that the evolution of the adult organism is the mechanical result of the predetermined interplay of those forces. The object of the present article is to point out that this conception is inadequate, and must be at least supplemented, if not replaced, by another view, namely, that the formative force is a generally diffused tendency, so that all parts inherently tend to complete by their own growth and modification the whole organism-a fact which finds a legitimate hypothetical expression in Darwin's Doctrine of pangenesis. The nature of the view here advanced will become clearer upon consideration of the evidence upon which it is based, and which is adduced below. The evidence that the formative force is diffused through all parts falls under three heads : 1. The process of regeneration in unicellular and multicellular bionts; 2. The phenomena of of the duplication of parts; 3. All forms of organic reproduction. Let us briefly consider these categories.

1. Regeneration.-All living organisms have, to a greater or less degree, the ability to repair injuries; indeed, we must regard the power of regeneration as coextensive with life, but the capacity varies enormously in the different species. In man the power is very small, though more extensive than is generally realized. Among Annelids are species, the individuals of which may be divided in two, and each piece can regenerate all that is needed to render it a complete worm. We sometimes see a small fragment of a plant, a single switch of a willow, for instance, regenerate an entire tree, roots, trunk, branches, leaves, flowers, and all. In the last instance a few cells possess a latent formative force, which we recognize by its effects, but cannot explain. We perceive, therefore, that each individual has, as it were, a scheme or plan of its organization to which it strives to conform. As long as it actually does so, the cells perform their routine functions; but when an injury destroys or removes some portion, then the remaining cells strive to conform again to the complete scheme, and to add the missing fragment. The act of regeneration of lost parts strikes the imagination almost as an intelligent pursuit by the tissues of an ideal purpose.

Our knowledge of the regeneration power has recently received important extensions through the noteworthy experiments of Nussbaum and Gruber," who have demonstrated, independently, the possibility of dividing unicellular animals so that each piece will regenerate the missing parts. In this manner the number of individuals can be artifically multiplied. For example: Nussbaum divided a well-isolated Oxytricha into two equal parts, either transversely or longitudinally, and found that the edges of the cut became soon surrounded with new cilia. Although some of the substance of the body, or even a nucleus, was lost through the operation yet, by the following day, the two parts converted themselves into complete animals with four nuclei and nucleoli (Nebenkerne) and the characteristic ciliary apparatus. “The head piece has formed a new hind end; the right half, a new left half.” The

* M. Nussbaum, Ueber spontane und kunstliche Zellteilung, Sitzungsb. d. neiderrh. Ges. f. Nat. u. Heilkunde, Bonn, 15, Dez., 1884.

* A. Gruber, Teber kunstliche Teilung bei Infusorien, Biol. Centralblatt, Bd. IV, No. 23, 717--722.

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