Regeneration

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REGENERATION

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COLUMBIA UNIVERSITY BIOLOGICAL SERIES. VII.

REGENERATION

BY
THOMAS   HUNT   MORGAN,   Ph.D.
PROFESSOR OF BIOLOGY, BRYN MAWR COLLEGE



New York
THE MACMILLAN COMPANY
LONDON: MACMILLAN & CO., Ltd.
1901
All rights reserved
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Copyright, 1901,
By THE MACMILLAN COMPANY.
Norwood Press
J. S. Cushing & Co.—Berwick & Smith
Norwood, Mass., U.S.A.

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To My Mother

PREFACE

This volume is the outcome of a course of five lectures on “Regenerationand Experimental Embryology,” given in Columbia University in January,1900. The subjects dealt with in the lectures are here more fullytreated and are supplemented by the discussion of a number of relatedtopics. During the last few years the problems connected with theregeneration of organisms have interested a large number of biologists,and much new work has been done in this field; especially in connectionwith the regenerative phenomena of the egg and early embryo. Thedevelopment of isolated cells or blastomeres has, for instance, arousedwidespread interest. It has become clearer, as new discoveries have beenmade, that the latter phenomena are only special cases of the generalphenomena of regeneration in organisms, so that the results have beentreated from this point of view in the present volume.

If it should appear that at times I have gone out of my way to attackthe hypothesis of preformed nuclear germs, and also the theory ofnatural selection as applied to regeneration, I trust that theimportance of the questions involved may be an excuse for the criticism.

If I may be pardoned a further word of personal import, I should like toadd that it has seemed to me that far more essential than each specialquestion with which the biologist has to deal is his attitude toward thegeneral subject of biology as a science. Never before in the history ofbiology has this been more important than at the present time, when weso often fail to realize which problems are really scientific and whichmethods are legitimate for the solution of these problems. The custom ofindulging in exaggerated and{viii} unverifiable speculation bids fair to dullour appreciation for hypotheses whose chief value lies in thepossibility of their verification; but those who have spent their timeand their imagination in such speculations cannot hope for long to holdtheir own against the slow but certain advance of a scientific spirit ofinvestigation of organic phenomena. The historical questions with whichso many problems seem to be connected, and for which there is norigorous experimental test, are perhaps responsible for the loose way inwhich many problems in biology are treated, where fancy too oftensupplies the place of demonstration. If, then, I have tried to use mymaterial in such a way as to turn the evidence against some of theuncritical hypotheses of biology, I trust that the book may have a widerbearing than simply as a treatment of the problems of regeneration.

I wish to acknowledge my many obligations to Professor H. F. Osborn andto Professor E. B. Wilson for friendly criticism and advice; and inconnection with the revision of the text I am greatly indebted toProfessor J. W. Warren, to Professor W. M. Wheeler, to Professor G. H.Parker, and to Professor Leo Loeb.

Bryn Mawr College, Pennsylvania,
June 11, 1901.
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CONTENTS

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REGENERATION

CHAPTER I
GENERAL INTRODUCTION

Although a few cases of regeneration were spoken of by Aristotle and byPliny, the subject first attracted general attention through theremarkable observations and experiments of the Abbé Trembley. Hisinterest was drawn to certain fresh-water polyps, hydras, that were newto him, and in order to find out if the organisms were plants or animalshe tried the effect of cutting them into pieces; for it was generallyknown that pieces of a plant made a new plant, but if an animal were cutinto pieces, the pieces died. Trembley found that the polyp, if cut intwo, produced two polyps. Logically, he should have concluded that thenew form was a plant; but from other observations, as to its method offeeding and of movement, Trembley concluded that the polyp was ananimal, and that the property of developing a new organism from a partmust belong to animals as well as to plants. “I felt,” he says,“strongly that nature is too vast, and too little known, for us todecide without temerity that this or that property is not found in oneor another class of organized bodies.”

Trembley’s first experiments were made in 1740, and the remarkableresults were communicated by letter to several other naturalists. Itcame about in this way that before Trembley’s memoir had appeared, in1744, his results were generally known, and several other observers hadrepeated his experiments, and extended them to other forms, and had evenpublished an account of their own experiments, recognizing Trembley,however, as the first discoverer. Thus Réaumur described, in 1742, anumber of other forms in which regeneration takes place; and Bonnet, in1745, also described some experiments that he had made during the fourpreceding years. Widespread interest was aroused by these results, andmany different kinds of animals were experimented with to test theirpower of regeneration. Most important of these new discoveries werethose of Spallanzani, who published a short preliminary statement of hisresults, in 1768, in his Prodromo.{2}

Trembley found that when a hydra is cut in two, the time required forthe development of the new individuals is less during warm than duringcold weather. He also found that if a hydra is cut into three or fourparts, each part produces a new individual. If these new hydras are feduntil they grow to full size, and are then again cut into pieces, eachpiece will produce a new polyp. The new animals were kept in some casesfor two years, and behaved in all respects as do ordinary polyps.

Trembley also found that if the anterior, or head-end, with itstentacles, is cut off, it also will make a new animal. If a hydra is cutlengthwise into two parts, the edges roll in and meet, and in an hour,or less, the characteristic form may be again assumed. New arms mayappear later on the new individual. If a hydra is split lengthwise intofour pieces, each piece will also produce a new polyp.

If the head-end only of a hydra is split in two, each half becomes a newhead, and a two-headed hydra results. If each of the new heads is splitagain, a four-headed hydra is produced; and if