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The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development   By:

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Heinemann's Scientific Handbooks

THE BIOLOGICAL PROBLEM OF TO DAY

HERTWIG

Heinemann's Scientific Handbooks

THE BIOLOGICAL PROBLEM OF TO DAY

PREFORMATION OR EPIGENESIS? THE BASIS OF A THEORY OF ORGANIC DEVELOPMENT

BY

PROFESSOR DR. OSCAR HERTWIG DIRECTOR OF THE SECOND ANATOMICAL INSTITUTE OF THE UNIVERSITY OF BERLIN

Authorized Translation

BY

P. CHALMERS MITCHELL, M.A.

WITH AN INTRODUCTION BY THE TRANSLATOR AND A GLOSSARY OF THE TECHNICAL TERMS

LONDON WILLIAM HEINEMANN 1896

[ All rights reserved ]

PREFACE

Shortly after the appearance of Dr. Oscar Hertwig's treatise 'Präformation oder Epigenese?' I published in Natural Science (1894) a detailed abstract of it. But the momentous issues involved in the problem of heredity, and the great interest excited by Dr. Weismann's theories, make it desirable that a full translation should appear. By the kindness of Dr. Hertwig and his German publisher, this is now possible. I have prefixed an introduction, written for those who are interested in the general problem, but who have little acquaintance with the technical matters on which the argument turns. In the actual translation I have tried no more than to give a faithful rendering of the German. After no little perplexity, I have rendered the German word Anlage as 'rudiment.' It is true, a double meaning has been grafted upon the English word, and it is widely employed to mean an undeveloped structure, without discrimination between incipient and vestigial character. I use it in the etymological sense, as an incipient structure. For the difficult words, Erbgleich and Erbungleich , a succession of new terms have been suggested. Here I use for the first term the word 'doubling,' for the second 'differentiating.'

P. C. M.

TRANSLATOR'S INTRODUCTION

Inquiry into the problems of heredity is beset with many difficulties, of which not the least is the temptation to argue about the possible, or the probable, rather than to keep in the lines of observation. Setting out from a laborious and beautiful series of investigations into the anatomy of the Hydromedusæ, Weismann came to think that the organic material from which the sexual cells of these animals arose was not the common protoplasm of their tissues, but a peculiar plasm, distinct in its nature and possibilities. In the course of several years, Weismann not only continued his own investigations in the many directions that his conception suggested, but made abundant use of that new knowledge of the nature and properties of cells which has been the feature of the microscopy of the last decade. His theory of the germplasm gradually grew, undergoing many alterations, so that even in its present form he regards it as tentative. Neglecting the numerous modifications and accessory hypotheses by which he has sought to adapt the theory to the phantasmagorial complexity of organic nature, the main outline of the theory is as follows: A living being takes its individual origin only where there is separated from the stock of the parent a little piece of the peculiar reproductive plasm, the so called germplasm. In sexless reproduction one parent is enough; in sexual reproduction equal masses of germplasm from each parent combine to form the new individual. The germplasm resides in the nucleus of cells, and Weismann identifies it with the nuclear material which microscopists have named chromatin, on account of the avidity with which it absorbs certain dyes. Like ordinary protoplasm, of which the bulk of cell bodies is composed, the germplasm is a living material, capable of growing in bulk without alteration of structure, when it has access to appropriate food. But it is a living material much more complex than protoplasm. In the first place, the mass of germplasm which is the starting point of a new individual consists of several, sometimes of many, pieces termed ids , each of which contains all the possibilities generic, specific, individual of a new organism... Continue reading book >>




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