The Biological Problem of To-day: Preformation Or Epigenesis?. Oscar Hertwig

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       Oscar Hertwig

      The Biological Problem of To-day: Preformation Or Epigenesis?

      The Basis of a Theory of Organic Development

      Published by Good Press, 2021

       [email protected]

      EAN 4064066188559

Table of Contents

       PREFACE

       TRANSLATOR'S INTRODUCTION

       THE BIOLOGICAL PROBLEM OF TO-DAY

       INTRODUCTION.

       PART I.

       WEISMANN'S THEORY OF THE GERMPLASM AND DOCTRINE OF DETERMINANTS.

       Criticism of the Germplasm Theory. [8]

       I. Objections to the Hypothesis of Differentiating Division.

       FIRST GROUP OF FACTS.—UNICELLULAR ORGANISMS.

       SECOND GROUP OF FACTS.—THE LOWER MULTI-CELLULAR ORGANISMS.

       THIRD GROUP OF FACTS.—THE PHENOMENA OF REPRODUCTION AND REGENERATION IN PLANTS AND ANIMALS.

       FOURTH GROUP OF FACTS.—THE PHENOMENA OF HETEROMORPHOSIS. [12]

       FIFTH GROUP OF FACTS.—PHENOMENA OF VEGETATIVE AFFINITY. [16]

       SUMMARY OF THE CONCLUSIONS IN THE FIRST SECTION.

       II. ARGUMENTS AGAINST THE DOCTRINE OF DETERMINANTS.

       PART II.

       THOUGHTS TOWARDS A THEORY OF THE DEVELOPMENT OF ORGANISMS. [17]

       INDEX AND GLOSSARY

PREFACE

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      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

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      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. Each id is a veritable microcosm, possessed of a historic architecture that has been slowly elaborated during the multitudinous series of generations that stretch backwards in time from every living individual. This microcosm, again, consists of a number of minor vital units called determinants, which cohere according to an orderly plan. A determinant exists for every part of the adult organism which is capable of being different in different individuals. And, lastly, each determinant consists of a number of ultimate particles called biophores, which eventually pass into the protoplasm of the cells in which they come to lie and direct the vital activities of these cells. A most important part of the theory is what it supposes to occur during the embryological development of the individual. The mass of germplasm derived from the germplasm of the parent lies in a mass of ordinary protoplasm. Both the protoplasm and the germplasm, by the assimilation of food, gradually increase in bulk until the adult size of the organism is reached. Along with the increase of size there occurs a gradual specialisation, during which the tissues, organs, and structure of the creature are attained. The simplest conception of this process is to regard the initial mass as a single cell, the nucleus of which is composed of the parental