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BEHAVIOR OF THE LOWER ORGANISMS

Il.

Vi.

Vil.

Columbia Gnibersity Biological Series

EDITED BY
HENRY FAIRFIELD OSBORN

AND

EDMUND B. WILSON

FROM THE GREEKS TO DARWIN
By Henry Fairfield Osborn

. AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES

By Arthur Willey

FISHES, LIVING AND FOSSIL. An Introductory Study
By Bashford Dean

THE CELL IN DEVELOPMENT AND INHERITANCE
By Edmund B. Wilson

THE FOUNDATIONS OF ZOOLOGY
By W. K. Brooks

THE PROTOZOA
By Gary N. Calkins

REGENERATION
By T. H. Morgan

. THE DYNAMICS OF LIVING MATTER

By Jacques Loeb

. ANTS: THEIR STRUCTURE, DEVELOPMENT AND BEHAVIOR

By W. M. Wheeler

. BEHAVIOR OF THE LOWER ORGANISMS.

By H. S. Jennings

COLUMBIA UNIVERSITY PRESS
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LEMCKE & BUECHNER
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COLUMBIA UNIVERSITY BIOLOGICAL SERIES. X.

BEHAVIOR OF THE LOWER
ORGANISMS

x BY

x
LF st eRNINGs

ASSISTANT PROFESSOR OF ZOOLOGY IN THE
UNIVERSITY OF PENNSYLVANIA

News Bork
COLUMBIA UNIVERSITY PRESS
1915

All rights reserved

Fak
a

992274
1.9.54

CoPYRIGHT, 1906,
By THE MACMILLAN COMPANY.

Set up and electrotyped. Published July, 1906.
Reprinted November, r9r5.

Norwood Press
J. 8. Cushing & Co. — Berwick & Smith Co.
Norwood, Mass., U.S.A.

PREFACE

THE objective processes exhibited in the behavior of the lower
organisms, particularly the lower animals, form the subject of the
present volume. The conscious aspect of behavior is undoubtedly
most interesting. But we are unable to deal directly with this by
the methods of observation and experiment which form the basis for
the present work. Assertions regarding consciousness in animals,
whether affirmative or negative, are not susceptible of verification.
This does not deprive the subject of consciousness of its interest, but
renders it expedient to separate carefully this matter from those
which can be controlled by observation and experiment. For those
primarily interested in the conscious aspects of behavior, a presenta-
tion of the objective facts is a necessary preliminary to an intelligent
discussion of the matter.

But apart from their relation to the problem of consciousness
and its development, the objective processes in behavior are of the
highest interest in themselves. By behavior we mean the general
bodily movements of organisms. These are not sharply distin-
guishable from the internal physiological processes; this will come
forth clearly in the present work. But behavior is a collective name
for the most striking and evident of the activities performed by
organisms. Its treatment as subsidiary to the problems of con-
sciousness has tended to obscure the fact that in behavior we have
the most marked and in some respects the most easily studied of
the organic processes. Such treatment has made us inclined to
look upon these processes as something totally different from the
remainder of those taking place in organisms. In behavior we are
dealing with actual objective processes (whether accompanied by
consciousness or not), and we need a knowledge of the laws con-
trolling them, of the same sort as our knowledge of the laws of
metabolism. In many respects behavior presents an exceptionally
favorable field for the study of some of the chief problems of life.
The processes of behavior are regulatory in a high degree. Owing
to their striking character, the way in which regulation occurs be-
comes more evident than in most other fields, so that they pre-
sent a most favorable opportunity for study of this matter. To

Vv

vi PREFACE
the regulatory aspect of behavior special attention is paid in the
following pages.

The modifiability of the characteristics of organisms has always
been a subject of the greatest importance in biological science. In
most fields the study of this matter is beset with great difficulties, for
the modifications require long periods and their progress is not easily
detectible. In the processes of behavior we have characteristics that
are modifiable with absolute ease. In the ordinary course of be-
havior variations of action are continually occurring, as a result of
many internal and external causes. We see quickly and in the gross
the changes produced by the environment, so that we have the best
possible opportunity for the study of the principles according to
which such changes occur. Permanent modifications of the methods
of action are easily produced in the behavior of many organisms.
When we limit ourselves to the subjective aspect of these, thinking
only of memory, or the like, we tend to obscure the general problem
involved. This problem is: What lasting changes are producible in
organisms by the environment or otherwise, and what are the princi-
ples governing such modifications? Perhaps in no other field do we
have so favorable an opportunity for the study of this problem,
fundamental for all biology, as in behavior. There seems to be no
a priori reason for supposing the laws of modification to be different
in this field from those found elsewhere. The matter needs to be
dealt with from an objective standpoint, keeping the general problem
in mind.

A study of behavior from the objective standpoint will help us
to realize that the activities with which we deal in other fields of
physiology are occurring in a substance that is capable of all the
processes of behavior, including thought and reason. This may aid
us to be on our guard against superficial explanations of physiological
processes.

But the chief interest of the subject of the behavior of animals
undoubtedly lies, for most, in its relation to the development of
psychic behavior, as shown by man. The behavior of the lowest
organisms must form a fundamental part of comparative psychology.

In the special field of the behavior of the lowest organisms the
foundations of our knowledge were laid by Verworn, in 1889, in his
“Psycho-physiologische Protistenstudien.” Binet, in his “ Psychic
Life of Micro-organisms” (1889), gave a most readable essay on the
subject, presenting it frankly from the psychical standpoint. Lukas,
in his “ Psychologie der niedersten Tiere” (1905), has recently again
dealt with the questions of consciousness in lower animals, the treat-
ment of objective processes being subsidiary to this matter.

The present work was designed primarily as an objective descrip-

PREFACE vii

tion of the known facts of behavior in lower organisms, that might wp
be used, not only by the general reader, but also as a companion
in actual laboratory experimentation. This description, comprising
Parts I and II of the present work, on the Protozoa and lower Meta-
zoa, respectively, was made as far as possible independent of any
theoretical views held by the writer; his ideal was indeed to present
an account that would include the facts required for a refutation of
any of his own general views, if such refutation is possible. These
designs have involved a fuller statement of details, with sometimes
their repetition under new experimental conditions, than would have
been necessary if the theoretical discussion had been made primary,
and only such facts adduced as would serve to illustrate the views
advanced. But the scientific advantages of the former method were
held to outweigh the literary advantages of the latter.

As originally written, this descriptive portion of the work was
more extensive, including, besides the behavior of the Protozoa and
Ccelenterata, systematic accounts of behavior in Echinoderms, Ro-
tifera, and the lower worms, together with a general chapter on the
behavior of other invertebrates. The work was planned to serve as
a reference manual for the behavior of the groups treated. But the
exigencies of space compelled the substitution of a chapter on some
important features of behavior in other invertebrates for the system-
atic accounts of the three groups last mentioned. The accounts of
the Protozoa and of the Coelenterata as representative of the lowest
Metazoa remain essentially as originally written.

' After this objective description was prepared, the need was felt
for an analysis of the facts, such as would bring out the general
relations involved. Part III is the result. Thus the conclusions set
forth in Part III are the result of a deliberate analysis of the facts
presented in a description which had been made before the conclu-
sions had been drawn. The selection of facts set forth in the de-
scriptive parts of the work has therefore been comparatively little
affected by the general theories held by the writer. The loss of
unity toward which this fact tends has perhaps its compensation in
the impartiality which it helps to give the descriptions.

The writer is conscious of the necessarily provisional nature of
most general conclusions at the present stage of our knowledge, and
the analysis given in Part III is presented with this provisional
character fully in mind. The reader should approach it in a similar
attitude.

Since the book is written primarily from a zoélogical standpoint,
it would be appropriate in some respects to entitle it “ Behavior of
the Lower Animals.” But the broader title seems on the whole best,
since the treatment of unicellular forms involves consideration of

s
viii PREFACE

many organisms that are more nearly related to plants than to
animals.

The figures have been drawn for the present work by my wife.
Figures not credited to other authors are either new or taken from
my own previous works.

The author is much indebted to the Carnegie Institution of
Washington for making possible a year of uninterrupted research,
devoted largely to studies preliminary to the preparation of this
work and to its actual composition. . He is further indebted for
the use of a number of figures first published by the Carnegie
Institution.

UNIVERSITY OF PENNSYLVANIA,
December 11, 1905.

CONTENTS

PART I
BEHAVIOR OF UNICELLULAR ORGANISMS

CHAPTER I
BEHAVIOR OF AMCEBA

1. Structure and Movements of Amceba_ : 2 Z ; é ‘ é I
2. Reactions of Amceba to Stimuli . 3 : 3 om te - > : : 6

A. Reaction to Contact with Solids ; : ¢ “ ° . mm ee
B. Reactions to Chemicals, Heat, Light, and Electricity . ; ° ° ° 9
C. How Ameeba gets Food . . . . ° ° . ey Fes

3. Features of General Significance in the Behavior of Ameeba . : - “ «) 19
Literature . ° . : . : ° . . . . . . . a |
CHAPTER II
BEHAVIOR OF BACTERIA

1. Structure and Movements : : . ; : : ° ° ° . ° 32 26
2. Reactions to Stimuli ; ‘ é . A 7 : ° : . <a
3. General Features in the Behavior of Bacteria : . : . ° ° . 38
Literature . e : - F a ; : = > ° ‘ ° ° « 40

CHAPTER III
BEHAVIOR OF INFUSORIA; PARAMECIUM
Structure; Movements; Method of Reaction to Stimuli

Introductory , : ‘ ‘ : ‘ : ‘ ‘ ‘ ‘ . ° ee

1. Behavior of Paramecium; Structure : ; é Fs . ° ‘ 2 rey
2. Movements . ; 7 > ‘ r - . seks ‘ » 44
3. Adaptiveness of the ovenients : : ‘ ‘ : : . . : » 45
4. Reactions to Stimuli . ‘ : ‘ . ‘ . F ° ‘ F ey
5. “Positive Reactions” . R . . ‘ ‘ F : : ° : hee |
Literature . RTS mae Oh PN Dea he Semen og fate Eg Pt ae Cw aera ee
CHAPTER IV
BEHAVIOR OF PARAMECIUM (CONTINUED)
Special Features of the Reactions to a Number of Different Classes of Stimuli
1. Reaction to Mechanical Stimuli é é F ‘ r ; - : é - 59
2. Reactions to Chemical Stimuli ‘ ‘ 6 F ‘ ° . ‘ , 62

x CONTENTS

3. Reactions to Heat and Cold . . : . ‘ ° ; ‘ . ‘ ‘
4. Reaction to Light . ‘ : . .
5. Orienting Reactions, to Water etous: to Gravity, and to Centrifugal F orce ‘
A. Reactions to Water Currents . ‘ 4 : ; . . ‘
B. Reactions to Gravity . 3 ; ‘ ; 7 . A . . F
C. Reaction to Centrifugal Force . i ° ° ° ‘

6. Relation of the Orientation Reactions to Other Réattions < - ‘
Literature . . = : ; 4 : F ats

CHAPTER V
BEHAVIOR OF PARAMECIUM (CONTINUED)
Reactions to Electricity and Special Reactions

1. Reactions to Electricity . : ; ‘ ° ; : :
A. Reaction to Induction Shocks . ; ; ; . é :
_ B. Reaction to the Constant Current . E 4 ‘ : ;
2. Other Methods of Reaction in Paramecium . c é ; - ‘ 4
Literature . 3 2 : ; : ; . : ; ° é F e ‘

CHAPTER VI
BEHAVIOR OF PARAMECIUM (CONTINUED)

Behavior under Two or More Stimuli ; Variability of Behavior; Fission and
Conjugation ; Daily Life; General Features of the Behavior

1. Behavior under Two or More Stimuli. ; " ; - ‘ ; ;
2. Variability and Modifiability of Reactions . ; A ° : °

3. Behavior in Fission and Conjugation . . A : x ;

4. The Daily Life of Paramecium : A . ° ‘

5. Features of General Significance in the Hebuvice at a PE fee ee
A. The Action System . , ‘ . °

B. Causes of the Reactions, and Effects padaised = reas : ee .
Literature . . . ° . . . . : . . +o .

CHAPTER VII
BEHAVIOR OF OTHER INFUSORIA
Action Systems. Reactions to Contact, to Chemicals, to Heat and Cold

1. The Action System ay : = ° = ° ‘ . . °
A. Flagellata . : ° . ° . F . : . ‘

B. Ciliata . . . * * . . . . . .
2. Reaction to Mechanical Stimuli ; s 4 3: 4 : ‘ ;
3. Reaction to Chemicals . see : ; ; . ‘ :

4. Reaction to Heat and Cold . é 5 " ; Z ‘ ‘ .
Literature . 3 = 5 - ‘ - . . A : F :

110
III
113
117
120
124
127

CONTENTS

CHAPTER VIII
REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY

1. Reactions to Light . ‘ : ; : ° ° °
A. Negative Reaction to Tighe: Stentor avalos . ° . ° .
B. Positive Reaction to Light: Euglena viridis . ° . : .

C. Negative and Positive Reactions compared " . .« .« «© -«

D. Reactions to Light in Other Infusoria : . ° ° ° ’

2. Reaction to Gravity and to Centrifugal Force . . . er ae .

Literature. . . ° . . : . : . . . ° .
CHAPTER IX

REACTIONS OF INFUSORIA TO THE ELECTRIC CURRENT

1, Diverse Reactions of Different Species of Infusoria . : - . °
A. Reaction to Induction Shocks . ; z - - . ° on
B. Reaction to the Constant Current ; : i - Port Seg e
2. Summary -. ‘ le lte . ° ’ .
3.. Theories of the esctinn to Electricity . . i pi eet wd eee wae te
Literature . F ; : 7 5 A ° ° e ° ° ° .
CHAPTER X

MODIFIABILITY OF BEHAVIOR IN INFUSORIA, AND BEHAVIOR UNDER
NATURAL CONDITIONS. Foop HABITs

. Modifiability of Behavior “ ° . . ° ° ° °

2. The Behavior of Infusoria under Natural Conditions “ ; Fs ‘ °

3. Food Habits . . . . . . . . . . . . .

Literature . . . . Meh . . . . . . ° . .
PART II

BEHAVIOR OF THE LOWER METAZOA

CHAPTER XI

INTRODUCTION AND BEHAVIOR OF CCELENTERATA

Introduction ; ‘ , x ‘ A - ‘ : . . °
ang oe of Coleuteeats : ; : 5 ‘ : : : ° .
- Action System. Spontaneous Activities ite . °
2. Conditions required for Retaining a Given Position: Righting Reactions, ate
3. General Reaction to Intense Stimuli " : : i A ‘ i »
4. Localized Reactions F ‘ ; F . : ° °
5. The Rejecting Reaction of na ‘Asiieionae . < F . re . .
6. Locomotor Reactions in Hydra and Sea Anemones . . ° : :

PAGE
128
128
134
141
141
149
150

151
151
152
162
164
169

170
179
182
187

188
188
189
192
197
198
202
203

xii CONTENTS

7. Acclimatization to Stimuli . . z . eae Se a “
8. Reactions to Certain Classes of Stimuli . : . ° ° - . °
A. Reactions to Electricity . P - F ° . :

B. Reactions to Gravity .
C. Reactions to Light ;
9. Behavior of Ccelenterates with Relation to Pood): ; : ‘
A. Food and Respiratory Reactions in Hydra ‘ : . .
B. Food Reactions in Medusze . . :
C. Food Reactions in Sea Anemones
10. Independence and Correlation of Behavior of Different Parts of the Body ‘

. Some General] Features of Behavior ir in Ceelenterates . 4 ; r :
Sees ; 5 A : : ‘ : ‘ ; A ~ é ° :
CHAPTER XII

GENERAL FEATURES OF BEHAVIOR IN OTHER LOWER METAZOA

1. Definite Reaction Forms (“ Reflexes”) . ° °
2. Reaction by Varied Movements, with Selection oun the Resnhing: Conditions
3. Modifiability of Behavior and its Dependence on Physiological States .

Literature. : news : 3 Ney Ary ors: les orev [PP %

PART III

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS, WITH A
DISCUSSION OF THEORIES

CHAPTER XIII

- (COMPARISON OF THE BEHAVIOR OF UNICELLULAR AND MULTICELLULAR ORGANISMS

CHAPTER XIV

TROPISMS AND THE LOCAL ACTION THEORY OF TROPISMS ‘ 2 > - 3
CHAPTER XV
Is THE BEHAVIOR OF THE LOWER ORGANISMS COMPOSED OF REFLEXES? i =

CHAPTER XVI
ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS

Introductory ‘ . Pe
1, The Causes and Dactaiwine Pacha of Sear sal Rascticus é 5 ;
A. The Internal Factors. . ,
(1) Activity does not require Preices crernat ‘Stimulation
(2) Activity may change without External Cause.
(3) Changes in saat: depend on Changes in Physiological States . ‘

233
238
250
259

260 .

265

277

CONTENTS xiii

PAGE
(4) Reactions to External Agents depend on Physiological States . 286
(5) The Physiological State may be changed by mae Internal

Processes . A 287
(6) The Physiological State eat bie staged by the ye of

External Agents “ ° . 287
(7) The Physiological State may be ebaliesd by the Activity of the

Organism . ; 288

(8) External Agents cause Reasive by changing the Physiological
State of the Organism ;
(9) The Behavior of the Organism at any pMoueut eens ones its

Physiological State at that Moment . ° . 288
(10) Physiological States change in Accordance with Certain ton - 289
(11) Different Factors on which Behavior Depends . ° . + 292

CHAPTER XVII

ANALYSIS OF BEHAVIOR (CONTINUED)

B. The External Factors in Behavior . ‘ : 3}: gt ee eS
(1) Relation to Physiological States ; : ° : « 293
(2) Change of Conditions as a Cause of Reaction . ° . + 293
(3) Reaction without External Change . : . . . - 296
(4) Reactions to Representative Stimuli . ‘ A ° ? . 296
(5) Relation of Reaction to Internal Processes . . 298
(6) Summary of the External Factors which produce or determine
Reactions . . ; ° ° F + 299

CHAPTER XVIII

ANALYSIS OF BEHAVIOR (CONTINUED)

2. The Nature of the Movements and Reactions ’ : . : . : + 300
A. The Action System . : ; : A ; F ‘ . ° + 300
B. Negative Reactions . : . ° + 301
C. Selection from the Conditions pnedaeed ‘ae Varied Movenwiiks ° . + 302
D. “Discrimination” . 5 . : . ‘ : : . + 304
E. Adaptiveness of Movements ‘ : . : . . ° . + 305
F. Localization of Reactions . . ‘ ‘ ‘ : . ° . - 306
G. Positive Reactions . . - ° . . . ° + 309
3. Résumé of the Fundamental Features of Betavion: . F ° . ° «Gee

CHAPTER XIX

DEVELOPMENT OF BEHAVIOR . . . . . . . . . ° + 314

-

CHAPTER XX

RELATION OF BEHAVIOR IN LOWER ORGANISMS TO PsYCHIC BEHAVIOR . . . 328

xiv CONTENTS

CHAPTER XXI
BEHAVIOR AS REGULATION, AND REGULATION IN OTHER FIELDS

1. Introductory . ‘ ° ‘ s . ; . > ag
2. Regulation in Behavior . ‘ : . a ee yiuane

A. Factors in Regulation in the Behavior of Lower Organisms °
3. Regulation in Other Fields . . es “te ee
4. Summary ; ° 7 eee ies oe ae ra @ Rt sieht =»

BIBLIOGRAPHY . . . . J . . . . . .

INDEX . . . . * . . . * . . . .

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PART I

THE BEHAVIOR OF UNICELLULAR ORGANISMS

CHAPTER I
THE BEHAVIOR OF AMCEBA
1. STRUCTURE AND MOVEMENTS OF AMG@EBA
THE typical Amoeba (Fig. 1) is a shapeless bit of jellylike protoplasm,
continually changing as it moves about at the bottom of a pool amid

the débris of decayed vegetation. From the main protoplasmic mass
there are sent out, usually in the direction of locomotion, a number of

Fic. 1.— Ameba proteus, after Leidy (1879) (slightly modified). ¢.v., contractile vacuole;
ec., ectosarc; en., endosarc; mu., nucleus; fs., pseudopodia.

lobelike or pointed projections, the pseudopodia (Fig. 1, ps.). These
are withdrawn at intervals and replaced by others. Within the mass
of protoplasm certain differentiations are observable. Covering the

outer surface there is usually, though not always, a transparent layer
B I

2 BEHAVIOR OF THE LOWER ORGANISMS

containing no granules; this is called the ectosarc (Fig. 1, ec.). Within
this the protoplasm is granular, and contains bits of substance taken as
food, vacuoles filled with water, and certain other structures. This

Fic. 2. — Ameba limax, after Leidy (1879).

granular protoplasm is known as the
endosarc (Fig. 1, en.). Within the
fluidlike endosarc we find two well-
defined structures. One is a disk-
like or rounded, more solid body,
known as the nucleus (Fig. 1, mu.).

The other is a spherical globule of water, which at intervals collapses,

emptying the contained water to the outside.

vacuole (Fig. 1, ¢.v.).°

This is the contractile

There are many different kinds of Amoebe, varying in their appear-

ance and structure.
three main types.

pseudopodia.

of this group.

For our purposes it will be sufficient to distinguish
In one type the form is very
irregular and changeable, and there are many
Of this type Ameba proteus (Fig.
1) is the commonest species. In a second type
the animal usually moves forward rapidly as a
single elongated mass, the protoplasm seeming very
fluid. Ameba limax (Fig. 2) is a representative
A third type consists of slowly

Fic. 3.— Ameba verru-
cosa, after Leidy (1879).

moving Amcebe, of nearly constant form, usually having wrinkles on the
surface, and with the thick ectosarc much stiffened, so that it does not

appear fluid in character.
is Ameba verrucosa (Fig. 3).

The commonest representative of this type

In its usual locomotion the movement of Amceba is in many respects
comparable to rolling, the upper surface continually passing forward

Fic. 4. — Paths of two par-
ticles attached to the outer sur-
face of Amceba. That portion
of the paths that is on the lower
surface is represented by broken
lines. The two particles were

seen to complete the circuit of-

the animal five or six times in
the paths shown. (The Amceba
was of course progressing; no
attempt is made to represent
this in the figure.)

and rolling under at the anterior end, so as to
form the lower surface. This may best be
seen by mingling soot with water containing
many Amcebe. Fine granules of soot cling
readily to the surface of Amoebz of the verru-
cosa type, and more rarely to Amcebe of other
types. Such particles which are clinging to
the upper surface move steadily forward till
they reach the anterior edge. Here they are
rolled over and come in contact with the sub-
stratum. They then remain quiet till the
Amoeba has passed across them. Then they
pass upward again at the posterior end, and
forward once more to the anterior edge. This

THE BEHAVIOR OF AMGBA 3

is repeated as long as the particles cling to the surface. Single particles
have been seen to pass thus many times around the body of the animal.
Diagrams of the movements of the particles clinging to the surface are
shown in Figs. 4 and 5s.

It is not only the outermost layer of the ectosarc that thus moves
forward. On the contrary, the whole substance of the Amceba, from the

Fic. 5. — Diagram of the movements of a particle attached to the outer surface of Ameba
verrucosa, in side view. In position 1 the particle is at the posterior end; as the Amceba pro-
gresses, it moves forward, as shown at 2, and when the Amceba has reached the position 3, the
particle is at its anterior edge, at x. Here it is rolled under and remains in position, so that
when the Amceba has reached the position 4, the particle is still at x, at the middle of its lower
surface. In position 5 the particle is still at the same place x, save that it is lifted upward
a little as the posterior end of the animal becomes free from the substratum. Now as the Amceba
passes forward, the particle is carried to the upper surface, as shown at 6. Thence it continues
forward, and again passes beneath the Amceba.

outer surface to the interior of the endosarc, moves steadily forward
as a single stream, only the part in contact with the substratum being at
rest. At times small particles are at first attached to the outer surface,
then gradually sink through the ectosarc into the endosarc. Through-
out the entire process of sinking inward the movement is steadily for-
ward.

It is clear, then, that Amoeba rolls, the upper surface continually pass-
ing across the anterior end to form the lower surface. The anterior
edge is thin and flat and is attached to the substratum, while the posterior

Fic. 6. — Diagram of the movements in a progressing Amoeba in side view. A, anterior
end; P, posterior end. The large arrow above shows the direction of locomotion; the other
arrows show the direction of the protoplasmic currents, the longer ones representing more rapid
currents. From a to x the surface is attached and at rest. From x to y the protoplasm is not
attached and is slowly contracting, on the lower surface as well as above. a, b, c, successive
positions occupied by the anterior edge. As the animal rolls forward, it comes later to occupy
the position shown by the broken outline.

end is high and rounded, and is not attached to the substratum. A
very good idea of the character of the movements of Amoeba may be

4 BEHAVIOR OF THE LOWER ORGANISMS

obtained in the following way: Pin two edges of a handkerchief to-
gether, so as to make a flat cylinder. Within this place some heavy
objects that will fill part of the cylinder, and lay the whole on a flat sur-
face. Now pull forward the upper surface of the cloth near the anterior
edge, a little at a time, bringing it in contact with the substratum. If
this process is continued, the handkerchief rolls slowly forward with thin
anterior edge and high posterior portion, — the weight within dragging
behind. The lower surface is at rest while the upper surface moves
forward. In all these respects the movement is like the locomotion of
Ameeba. A diagram of the movement of Amceba as it would appear
in side view is given in Fig. 6.

While typically all the currents are forward in a progressing Amceba,
any portion of the protoplasm may be excluded temporarily from the
currents. This is especially common at the posterior end or tail, which
is often composed of quiet protoplasm, covered with wrinkles or papille
But the substance of the tail is in the course of time drawn into the cur-
rents and passes forward.

In the formation of pseudopodia the movement is much like that at
the anterior end of the body. If the pseudopodium is in contact with the
substratum, the upper surface moves forward while the lower surface is
at rest. If the pseudopodium is sent forth freely into the water, its
entire surface moves outward, in the same direction as the tip. These
movements have been determined by observing the motion of particles
attached to the outer surface of extending pseudopodia.

In some Amcebe, according to Rhumbler (1898, 1905), the external
protoplasmic currents turn backward at the sides of the anterior end,
so that there is produced a fountainlike arrangement, an internal
current forward, external currents backward. Such currents resemble
those due to local decrease of surface tension in a drop of inorganic fluid.

Through sucha local

= decrease the tension
a“ ‘ Me po pulling along the
surface is lessened

in a given region,
e ; j , so that the remain-
Fic. 7.— Currents in a drop of fluid when the surface tension d f th rf
is decreased on one side. A, the currents in a suspended drop, @€r Of the suriace
when the surface tension is decreased at a. After Berthold: 3B, film is pulling more
axial and surface currents in a drop of clove oil in which the Feet h
surface tension is decreased at the side a. The drop elongates Strongly; it there-
spe mg “ a ee nahh » that an anterior (¢) and a_ fore drags the sur-
r 1m; e.
ee ies face layer of the

drop away from the point of lowered tension. The result is that cur-
rents pass on the surface in all directions away from this point (Fig. 7).

THE BEHAVIOR OF AMGBA 5

At the same time the inward pressure is decreased in the region of
lowered tension, while elsewhere the pressure remains the same. Hence
the internal fluid of the drop is pressed out toward the region where the
film is weakened; a current flows in the central part of the drop toward
this point. This current may produce a projection at the point of
lowered tension, provided the surface currents do not carry the fluid back
as fast as it is brought forward.

It was long supposed that the movements of all sorts of Amcebze
were of this character. As a natural conclusion, it was commonly held
that locomotion and the formation of pseudopodia in Amoeba are due
to a local decrease in surface tension at the region of forward move-
ment. As our account shows, most Amoebez do not move at all as do
liquid drops whose movements are produced through changes in: surface
tension.t Rolling movements with all currents forward cannot be pro-
duced experimentally through local changes in the surface tension of a
drop of fluid. It is necessary, therefore, to abandon the surface tension
theory for those Amcoebe that move in the way shown in Fig. 6. If the
theory is still maintained for the Amcebe with backward currents; this
involves holding that the movements are due to fundamentally dif-
ferent causes in different Amcoebe; this is the view maintained by
Rhumbler (1905). :

While most Amcebe roll as they progress, different species differ greatly
in special features of their movements. The species of the verrucosa
type (Fig. 3) move slowly and change
form very little, not sending out
pseudopodia. ‘Those of the limax
type (Fig. 2) move more rapidly and
change form more frequently, but they
rarely send out pseudopodia. Finally,
in the proteus type (Fig. 1) the form
is excessively changeable, many pseu-
dopodia extending and retracting.

Fic. 8. — Ameba velata, showing the
2 antennalike anterior pseudopodium pro-
Many Amoebze show what might be jecting freely into the water. After

called specialized habits in their usual P¢enard (+99):

movements. For example, Ameba angulata and Ameba velata usually
send forth at the anterior edge a pseudopodium which extends freely into
the water and waves back and forth, serving as a feeler or antenna

1 According to Rhumbler (1905), such movements are most readily seen in a species of
Ameeba living parasitically in the intestine of the cockroach. Whether the currents on the
upper surface are actually backward, where the interior currents are forward, as is required
if the movements are to be explained by local decrease of surface tension, has not been
shown.

6 BEHAVIOR OF THE LOWER ORGANISMS

(Fig. 8). Many other special peculiarities of movement are described
in the great work of Penard (1902) on these organisms.

2. REACTIONS OF AMGEBA TO STIMULI

The conditions under which Ameeba lives are not always the same,
and as the conditions change, the behavior of Amoeba changes also.
Such changes in behavior are usually called reactions, while the external
agents that induce them are called stimuli.

A. Reaction to Contact with Solids

One of the commonest stimuli is that due to contact with a solid
object. Ifa solid body strikes strongly against one side or one end of a
moving Ameeba, the part affected contracts

and releases its hold on the substratum,

and the internal currents start away from

a it. The Ameeba changes its course and

moves in another direction. We may call

this a negative reaction, since it takes the

animal away from the source of stimulation.

This reaction can be produced experi-

% mentally by touching the animal, under the

microscope, with the tip of a glass rod

drawn to a minute point (Fig. 9). The

animal does not, as a rule, move directly

Fic. 9. — Negative reaction to away from the side touched, but merely in
mechanical stimulation in Amoeba. some other direction than toward this side.
An Amceba advancing in the direc- z R
tion shown by the arrows is stimu- If we touch it at the anterior edge, the part
lated with the tip of a glass rod at touched stops and contracts, while the cur-
its anterior edge (a). Thereupon 2 : F
this part is contracted, the currents ent turns to one side at this point, so that
are changed, and a new pseudo- the animal moves at an angle with its for-
podium sent out (0). 4 cS

mer course (Fig. 9). Often the course is
altered only a little in this way. But if all of one side or one end is
strongly stimulated, then a pseudopodium may be sent out on the side
opposite, so that the animal moves almost directly away from the stimu-
lated region (Fig. 10).

By repeatedly stimulating Amoeba it is possible to drive it in any
desired direction. The advancing edge is touched with the rod; it
thereupon withdraws. A new pseudopodium is sent out elsewhere.
If this does not lead in the direction desired, it is touched, causing retrac-
tion, whereupon the Amoeba tries a new direction. This continues

THE BEHAVIOR OF AMCGBA 7

till a pseudopodium is sent out in the direction desired by the experi-
menter. The animal may now be compelled to follow a definite straight —
course, by stimulating any pseudopodium
which tends to diverge from this course.

If the posterior end of a moving
Ameeba is stimulated, the animal con-
tinues to move forward, usually hastening
its course a little. The posterior end is
of course already contracted, and the
new stimulation merely causes it to con-
tract a little more.

The negative reaction is of course
the method by which Ameeba avoids
obstacles. If an Amceba in creeping
comes against a small solid body, the ,

/ . Fic. 10. — Negative reaction to a
reaction is often less sharply defined than mechanical stimulus when the entire
in the cases which we have thus far anterior end is strongly stimulated. a

f r ‘ and 8, successive stages. The arrow
described. A typical example is shown , shows the original direction of
i i i motion; the arrows in @ show the
i Big. ed ep cee Ppocia Wars: curtélite immediately after stimulation.
in contact at the middle of its anterior jn 4 a new tail (¢’) has been formed
edge with the end of a dead alga fila- from the former anterior end, uniting

with the old tail (#).

ment. Thereupon the protoplasm ceased

to flow forward at the point of contact c, while on each side of
this point the motion continued as before. In a short time, there-
fore, the animal had the form and position shown by the broken
outline in Fig. 11; the filament projected deeply into a notch at the
anterior edge. Motion continued in this manner would have divided
the Ameeba into two parts. But soon motion ceased on one side (x),
while it continued on the side y. The currents in x became reversed

ox
io

Fic. 11. — Method by which Amceba avoids an obstacle.

and flowed around the end of the filament into y, as shown at B, Fig. 11.
Thus the animal had avoided the obstacle by reversing a part of the
current and flowing in another direction.

But not all mechanical stimuli cause a negative reaction. Some-

8 BEHAVIOR OF THE LOWER ORGANISMS

times Amceba, on coming in contact with a solid body, turns and moves
toward it, —responding thus by a positive reaction. At times an
Ameeba which is moving along on the glass slip used in microscopic
work comes in contact by its upper surface with the under surface of
the cover-glass. Thereupon it sometimes pushes forth a pseudopodium

Fic. 12.— Ameba velata passing from the slide to the cover-glass, side view. After Penard
(1902). At @ the animal is creeping in the usual way, with the tentaclelike pseudopodium
projecting into the water. At b the pseudopodium has reached the cover-glass and attached
itself. At c the animal has released its hold on the slide, and is now attached to the cover alone.

on this under surface; the pseudopodium attaches itself; the Amoeba
releases its hold on the slide, and now continues its course on the under
side of the cover-glass. Penard (1902) has observed this in Ameba
velata, when the long, tentaclelike anterior pseudopodium of this ani-
mal comes during its feeling movement in contact with the cover-glass.
The process is represented in Fig. 12. In a similar manner Amcebe
frequently pass to the under side of the surface film of water, creeping
on this as if it were a solid body.

Under certain circumstances Amoeba seems especially disposed
toward this positive reaction. Sometimes an Ameeba is left suspended
in the water, not in contact with
anything solid. Under such cir-
cumstances the animal is as nearly
completely unstimulated as it is
possible for an Amceba to be; it
is contact only with the water,
and that uniformly on all sides.
But such a condition is most un-
favorable for its normal activities ;
it cannot move from place to
place, and has no opportunity to
obtain food. Amoeba has a
method of behavior by which it
meets these unfavorable condi-

Fic. 13.— Amba proteus suspended in the tions. It usually sends out long,
vis Soest Peat Tay Cea). extended slender pseudopodia in all direc-

tions, as illustrated in Fig. 13.
The body may become reduced to little more than a meeting point for
these pseudopodia. It is evident that the sending out of these long arms

THE BEHAVIOR OF AMGBA 9

greatly increases the chances of coming in contact with a solid body, and
it is equally evident that contact with a solid is under the circumstances
exactly what will be most advantageous to the animal. As soon as the
tip of one of the pseudopodia does come in contact with something
solid, the behavior changes (Fig. 14). The tip of the pseudopodium

— — —. (“4 —e
a i) c

Fic. 14. — Method by which a floating Amoeba passes to a solid.

spreads out on the surface of the solid and clings to it. Currents of
protoplasm begin to flow in the direction of the attached tip. The
other pseudopodia are slowly withdrawn into the body, while the body
itself passes to the surface of the solid. After a short time the Amceba,
which had been composed merely of a number of long arms radiating
in all directions from a centre, has formed a collected flat mass, creep-
ing along a surface in the usual way. This entire reaction seems a re-
markable one in its adaptiveness to the peculiar circumstances under
which the organism has been placed.
Positive reactions toward solid bodies are particularly common in
the process of obtaining food. In our account of the food reactions we
shall give examples of striking and long-continued reactions of this sort.

B. Reactions to Chemicals, Heat, Light, and Electricity

Reactions to Chemicals. — If a strong chemical in solution diffuses
against one side or end of the body, the Amceba contracts the part af-
fected, releasing it from the substratum, while the protoplasmic cur-
rents start in some other direction. The animal has thus changed its
course. The reaction to chemicals can best be shown in the following
way. The tip of a capillary glass rod is moistened, then dipped in some
powdered chemical, preferably a colored one, such as methyline blue.
This tip is then, under the microscope, brought close to one side of an
Amoeba in an uncovered drop of water. As soon as the diffusing
chemical comes in contact with one side of the body, the reaction occurs.
Chemicals that are fluid may be drawn into an excessively fine capillary
tube and the tip of this held near the Amoeba. Some of the variations
in the reactions to chemicals are shown in Fig. 15.

10 BEHAVIOR OF THE LOWER ORGANISMS

Such experiments show that Amceba is very sensitive to changes in
the chemical composition of the water surrounding it, and is inclined
to move away whenever it comes to a region in which the water differs
even slightly from that to which it is accustomed. It has been shown
to react negatively when the following substances come in contact with
- one side of its body: methyline blue, methyl green, sodium chloride,
sodium carbonate, potassium nitrate, potassium hydroxide, acetic acid,
hydrochloric acid, cane sugar, distilled water, tap water, and water

2
d

Fic. 15. — Variations in the reactions of Amceba to chemicals. The dotted area represents
in each case the diffusing chemical. The arrows show the direction of the protoplasmic currents.

a. A little methyl green diffuses against the anterior end of an Amceba. The latter reacts
by sending out a new pseudopodium at one side of the anterior end and moving in the direction
so indicated.

6. A solution of NaCl diffuses against the right side of a moving Amceba (1). The side
affected contracts and wrinkles strongly, while the opposite side spreads out (2), the currents
flowing as shown by the arrows.

c. A solution of NaCl diffuses against the anterior end of an advancing Amceeba. A broad
pseudopodium, shown by the dotted outline, pushes out from the posterior region, above the end,
and the course is reversed.

d. A solution of methyline blue diffuses against the anterior end of an Amceba (1). There-
upon a pseudopodium is sent out on each side of the posterior end at right angles with the original
course (2). Into these the entire substance of the animal is drawn (3).

from other cultures than that in which the Amoeba under experimen-
tation lives.

Reaction to Heat. — If one side of an Ameeba is heated, it reacts in
the same negative way as to chemicals or to a mechanical shock. The
reaction to heat may be observed as follows: An Amoeba creeping
on the under surface of the cover-glass is chosen for the experiment.
The point of a needle is heated in a flame and placed against the cover-
glass in front of the Amceba, or a little to one side of it. If the needle
is not brought too close so as to affect the whole body instead of only

THE BEHAVIOR OF AMGBA It

aioe accsta viseceh ln stctes ies ap nes sks ak @

&

NRA st

Fic. 16.— Reaction of Amceba
to light, after Davenport (1897).
The Ameeba was first moving in the
direction indicated by the arrow x.
Light coming from the direction
shown by the arrow a was then
thrown upon it. It changed its
course, occupying successively the
positions 1, 2,3,4. The direction of
the light was successively changed as
indicated by the arrows b, c, d; the
numbers 5-14 show the successive
positions occupied by the animal. It
will be observed that in every case as
soon as the direction of the light is
changed, the Amceba changes its
course in a corresponding way, so as
to retreat steadily from the source of
light.

effect on Amceba.
seem better performed in the dark; strong
light interferes with them seriously. Rhum-
bler (1898) observed that if Amoebe are
suddenly subjected to light while busy feed-
ing on Oscillaria filaments, they cease to
feed, and even give out the partly ingested filaments.
Harrington and Leaming (1900) found that ordinary
white light thrown on a moving Amceba causes it to
come to rest at once.
while in red light the movements are as free as in dark-
ness. Other colors have intermediate effects. Engelmann
(1879) found that sudden illumination causes an extended
Pelomyxa (which is merely a very large Amoeba) to con-
tract suddenly. It is well known that exposure to strong
light is destructive to most lower organisms.

In correspondence with the fact that light interferes
with its activities, we find that Amoeba moves away from
a source of strong light.
on it from one side, it moves, as Davenport (1897) shows,
in the opposite direction.

done side, the animal responds by
contracting the part affected and
moving in some other direction.

Reactions to Light.— Light has a peculiar

In general its functions

Blue light acts in the same way,

If the sun is allowed to shine

It thus moves in a general
way in the same direction as the rays of
light (Fig. 16). It is a peculiar fact that
experiments so far have not shown a
negative reaction to occur when light is
thrown from directly above or below on
one side or end of an Amceba. The fact
that the whole body contracts when illumi-
nated, as shown by the work of Engel-
mann (1879) on Pelomyxa, would lead us
to expect that when a portion of the body
is illuminated, this would contract, pro-
ducing thus a negative reaction. But this
has not been demonstrated. The experi-
mental difficulties are great, and this may
account for the lack of positive results.
If future work substantiates the fact that
light falling obliquely on one side causes

12 BEHAVIOR OF THE LOWER ORGANISMS

a reaction, while light falling from above or below on one side causes
none, this would seem to indicate that the direction of the rays in
passing through the body has something to do with determining the
direction of locomotion. But in the myxomycete plasmodium, which
resembles Amoeba in its movements and in many other respects, light
falling from above or below on a part of the body does produce a
negative reaction, — the withdrawal of: the part affected. Probably
further experimentation will show the same thing to be true in Amceba.

Reaction to Electricity. — Electric currents probably form no part of
the normal environment of Amceba, yet the animal reacts in a very defi-
nite way when a continuous current is passed through the water con-
taining it. That side of the body which is directed toward the ‘positive
pole or anode contracts as if the animal were strongly stimulated
here. Then a pseudopodium starts out somewhere on the side directed

HOOeg

Fic. 17. — Reaction of Ameeba to the electric current. The arrows show the direction of
the protoplasmic currents; at 1 the direction of movement before the current acts is shown.
2, 3, 4, successive positions after the current is passed through the preparation.

toward the negative pole or cathode, and the Ameeba creeps in that direc-
tion (Fig. 17). The reaction takes place throughout as if the Amoeba
were strongly stimulated on the anode side. If the electric current is
made very strong, the anode side contracts still more powerfully, and
the Amceba bursts open on the opposite side. The current is thus very
injurious.

C. How Ameba gets Food

In the water in which Amceba lives are found many other minute
animals and plants. Upon these Amceba preys, taking indifferently an
animal or a vegetable diet. Its behavior while engaged in obtaining
food is very remarkable for so simple an animal.

Spherical cysts of Euglena are a common food with Ameba proteus.
These cysts are smooth and spherical, easily rolling when touched, so
that they present considerable difficulties to an Amoeba attempting to

THE BEHAVIOR OF AMG@BA 13

ingest them. One or two concrete cases will illustrate the behavior of
Amceba when presented with the problem of obtaining such an object
as food.

A spherical Euglena cyst lay in the path of an advancing Ameba
proteus. The latter came against the cyst and pushed it ahead a short
distance. The cyst did not cling to the protoplasm, but rolled away
as soon as it was touched, and this rolling away continued as long as the
animal moved forward. Now that part of the Amceba that was imme-
diately behind the cyst stopped moving, so that the cyst was no longer
pushed forward. At the same time a pseudopodium was sent out on
each side of the cyst (Fig. 18), so that the latter was enclosed in a little
bay. Meanwhile, a thin sheet of es passed from the upper
surface of the Amceba
over the cyst (Fig.
18, 2). The two lat-
eral pseudopodia be-
came bent together at
their free ends; the
cyst was thus held so
that it could not roll
away. The pseudo-
podia and the over-
lying sheet of proto- S z
plasm fused at their Fic.18.—Ameeba ingesting a Euglena cyst. 1, 2, 3, 4, succes-
free en ds, so that the sive stages in the process.
cyst was completely enclosed, together with a quantity of water. It
was then carried away by the animal.

Ameeba, does not always succeed in obtaining its food so easily as
in the case described. Often the cyst rolls away so lightly that the
animal fails to grasp and enclose it. In such a case Amoeba may con-
tinue its efforts a long time.

Thus, in a case observed by the author, an Ameba proteus was moy-
ing toward a Euglena cyst (Fig. 19). When the anterior edge of the
Amoeba came in contact with it, the cyst rolled forward a little and
slipped to the left. The Amoeba followed. When it reached the cyst
again, the latter was again pushed forward and to the left. The Amoeba
continued to follow. This process was continued till the two had trav-
ersed about one-fourth the circumference of a circle. Then (at 3) the
cyst when pushed forward rolled to the left, quite out of contact with
the animal. The latter then continued straight forward, with broad
anterior edge, in a direction which would have taken it away from the
food. Buta small pseudopodium on the left side came in contact with

14 BEHAVIOR OF THE LOWER ORGANISMS

the cyst, whereupon the Amceba turned and again followed the rolling
ball. At times the animal sent out two pseudopodia, one on each side
the cyst (as at 4), as if trying to enclose the latter, but the spherical cyst
rolled so easily that this did not succeed. . At other times a single, long,
slender pseudopodium was sent out, only its tip remaining in contact
with the cyst (Fig. 19, 5); then the body was brought up from the rear,
and the food pushed farther. Thus the chase continued until the roll-
ing cyst and the following Amoeba had described almost a complete

Fic. 19.— Ameeba following a rolling Euglena cyst. The figures 1-9 show successive
positions occupied by Amceba and cyst.

circle, returning nearly to the point where the Amoeba had first come
in contact with the cyst. At this point the cyst rolled to the right as it
was pushed forward (7). The Ameeba followed (8, 9). This new path
was continued for some time. The direction in which the ball was
rolling would soon have brought it against an obstacle, so that it seemed
probable that the Amoeba would finally secure it. But at this point,
after the chase had lasted ten or fifteen minutes, a ciliate infusorian
whisked the ball away in its ciliary vortex.

Such behavior makes a striking impression on the observer who

THE BEHAVIOR OF AMGBA 15

sees it for the first time. The Amoeba conducts itself in its efforts to
obtain food in much the same way as animals far higher in the scale.
In cultures containing many Amcebe and many Euglena cysts it is not
at all rare to find specimens thus engaged in following a rolling ball of
food. Sometimes the chase is finally successful; sometimes it is not.
Many of the cysts are attached to the substratum. Amoeba often
attempts to take such cysts as food, sending pseudopodia on each side
of and above them, in the usual way, then covering them completely
with its body. But it finally gives up the attempt and passes on.
Sometimes when a single pseudopodium comes in contact with a
cyst, this pseudopodium alone reacts, stretching out and pushing the
cyst ahead of it and keeping in contact with it as long as possible. Mean-
while the remainder of the Amoeba moves in some other direction (Fig.
20). Finally the pseudopodium is pulled by the rest of the body away

| O
8 \ :
ect 2 Ne 3 Po 4

Fic. 20.— A single pseudopodium (x) reacts positively to a Euglena cyst, its protoplasm
flowing in the direction of the cyst and pushing it forward, while the remainder of the Amceba
moves in another direction. 1-4, successive forms taken. At 4 the reacting pseudopodium
is pulled away from the cyst, whereupon it contracts.

from the cyst. Again, two pseudopodia on opposite sides of the body
may each come in contact with a cyst. Each then stretches out, pull-
ing a portion of the body with it, and follows its cyst. Soon the body
comes to form two halves connected only by a narrow isthmus. Finally
one half succeeds in pulling the other away from its attachment to the
bottom. The latter half then contracts, and the entire Amceba follows
the victorious pseudopodium.

Amoebe frequently prey upon each other. Sometimes the prey is
contracted and does not move; then there is no difficulty in ingesting
it. Such a case has been described and figured by Leidy (1879, p. 94,
and Pl. 7, Figs. 12-19). But the victim does not always conduct itself
so passively as in this case, and sometimes finally escapes from its
pursuer. This may be illustrated by a case observed by the present
writer (Fig. 21).

BEHAVIOR OF THE LOWER ORGANISMS

16

‘advose yeuy sainjdeoer syy pue vqaoury painjdvo ay} jo advosa ‘iayjoue Aq eqaury auo jo uoNsadut pue ‘ainjdvo Ymsing — ‘12 ‘oly

THE BEHAVIOR OF AM@BA 17

I had attempted to cut an Amceba in two with the tip of a fine glass
rod. ‘The posterior third of the animal, in the form of a wrinkled ball,
remained attached to the rest of the body by only a slender cord, —
the remains of the ectosarc. The Amoeba began to creep away, drag-
ging with it this ball. This Amoeba. may be called a, while the ball
will be designated 6 (see Fig. 21).. A larger Amoeba (c) approached,
moving at right angles to the path of the first specimen. Its path acci-
dentally brought it in contact with the ball 6, which was dragging past
its front. Amoeba c thereupon turned, followed Amceba a, and began
to engulf the ball 6. A cavity was formed in the anterior part of Amoeba
c, reaching back nearly or quite to its middle, and much more than
sufficient to contain the ball 6. Amoeba @ now turned into a new path;
Amoeba c¢ followed (Fig. 21, at 4). After the pursuit had lasted for
some time the ball 6 had become completely enveloped by Amceba c.
The cord connecting the ball with Amceba a broke, and the latter went
on its way, disappearing from our account. Now the anterior opening
of the cavity in Amoeba c became partly closed, leaving only a slender
canal (5). The ball 6 was thus completely enclosed, together with a quan-
tity of water. There was no adhesion between the protoplasm of 6 and
c; on the contrary, as the sequel will show clearly, both remained inde-
pendent, c merely enclosing 0.

Now the large Amoeba c stopped, then began to move in another
direction (Fig. 21, at 5-6), carrying with it its meal. But the meal —
the ball b — now began to show signs of life, sent out pseudopodia, and be-
came very active; we shall therefore speak of it henceforth as Amceba 0.
It began to creep out through the still open canal, sending forth its
pseudopodia to the outside (7). Thereupon Ameceba c sent forth its
pseudopodia in the same direction, and after creeping in that direction
several times its own length, again enclosed b (7, 8). The latter again
partly escaped (9), and was again engulfed completely (10). Ameeba ¢
now started again in the opposite direction (11), whereupon Amceba 0,
by a few rapid movements, escaped from the posterior end of Amoeba
c, and was free, — being completely separated from ¢ (11, 12). There-
upon ¢ reversed its course (12), overtook b, engulfed it completely again
(13), and started away. Amoeba 0 now contracted into a ball and re-
mained quiet for a time. Apparently the drama was over. Amoeba ¢
Went on its way for about five minutes without any sign of life ind. In
the movements of ¢ the ball became gradually transferred to its poste-
rior end, until there was only a thin layer of protoplasm between 6 and
the outer water. Now b began to move again, sent pseudopodia through
_ the thin wall to the outside, and then passed bodily out into the water
(14). This time Amceba c did not return and recapture b. The two

Cc

18 BEHAVIOR OF THE LOWER ORGANISMS

Amcebe moved in opposite directions and became completely separated.
The whole performance occupied about fifteen minutes.

Such behavior is evidently complex. An analysis into simple re-
actions to simple stimuli is difficult if possible at all. We shall return
to this matter later.

The method of food-taking illustrated in the behavior described is
characteristic for Amoebee of the proteus and limax types. It is some-
times said that these Amoebe take food at the wrinkled posterior end.
This, if true at all, is certainly rare; the author has never observed it,
though he has seen food taken in dozens of cases. The essential fea-
tures. of the food reaction seem to be the movement of the Amceba
toward the food body (long continued, in some cases), the hollowing out
of the anterior end of the Amceba, the sending forth of pseudopodia
on each side of and above the food, and the fusion of the free
ends of the pseudopodia, thus enclosing the food, with a quantity
of water. The reaction is thus complex; at times, as we have seen,
extremely so.

In the process of taking food which we have just described there is
no adherence between the protoplasm and the food body. But in
Ameba verrucosa and its relatives foreign objects do adhere to the sur-
face of the body, and this adherence is of much assistance in obtaining
food. It partly compensates for the lack of pseudopodia in these species.
- But it is not alone food substances that cling to the surface of the body.
Particles of soot and bits of débris of all sorts become attached in the
same way. Not all these substances are taken into the body as food,
so that adhesion to the surface does not account for food-taking. For
this an additional reaction is necessary.

Food-taking in Ameba verrucosa often occurs as follows: The ani-
mal in its progress comes in contact with a small food body, such as a
Euglena cyst. This adheres to the surface, and may pass forward on
the upper surface of the body to the anterior edge, in the way described
on a previous page. At the same time it begins to sink slowly into the
body, surrounded by a layer of ectosarc. When it has rounded the
anterior edge, the Amceba passes over it; then the food body passes up-
ward again at the posterior end and forward on the upper surface. It
is now sunk still more deeply into the protoplasm, and by the time it
reaches the anterior edge again it has usually passed completely into the
endosarc, together with the layer of ectosarc enveloping it. In this way
the author has seen Ameba verrucosa ingest various algz, small flagel-
lates, Euglena cysts, and a small Ameceba of the proteus type. Indifferent
particles, such as bits of soot, which are attached to the surface at the
same time, are not taken in.

THE BEHAVIOR OF AMGBA 19

Sometimes the taking of food is in Ameba verrucosa a much more
complicated process than that just described. Rhumbler (1898) has
given a very interesting account of the way in which this species feeds
upon filaments of alge
many times its own
length (Fig. 22). The
animal settles upon
the middle of an
Oscillaria filament, en-
velopes it, and length-
ens out along it (ca).
Then one end bends
over (b), so that a loop
is formed in the fila-
ment (c). The Amoeba
then stretches out on
the filament again,

bends it over anew, Fic. 22.— Ameba verrucosa coiling up and ingesting a fila-
and the process is ment of Oscillaria. After Rhumbler (1898). The letters a to g

repea hed} amtil the fla- show successive stages in the process.
ment forms a close coil within the Amceba (c to g, Fig. 22). Leidy
(1879, p. 86) has given a similar account of the method of feeding on
filaments of alge in Dinamceba.

Filaments that have been partly coiled up are often ejected when
light is thrown upon the animal (Rhumbler, 1898).

3. . FEATURES oF GENERAL SIGNIFICANCE IN THE BEHAVIOR
oF AMCEBA

We find that the simple naked mass of protoplasm reacts to all
classes of stimuli to which higher animals react (if we consider auditory
stimulation merely a special case of mechanical stimulation). Mechan-
ical stimuli, chemical stimuli, temperature differences, light, and elec-
tricity control the direction of movement, as they do in higher animals.
In other words, Amoeba has some method of responding to all the chief
classes of life conditions which it meets.

The cause of a reaction — that is, of a change of movement — is in
most cases some change in. the environment, due either to an actual
alteration of the conditions, or to the movement of the animal into new
conditions. This is notably true-of the reactions to mechanical, chemi-
cal, and thermal stimuli. In the reactions to light and the electric cur-

B0.., BEHAVIOR OF THE LOWER ORGANISMS

rent this is not so evident at first view. The Amoeba reacts even though
the light or current remains constant. But if, as appears to be true, the
_stimulation occurs primarily on that side on which the light shines, or on
the anode side in the reaction to electricity, then it is true that even in
these cases the reacting protoplasm is subjected to changes of conditions.
Since the movement of the Ameceba is of a rolling character, the proto-
plasm of the anterior end and that of the posterior end continually in-
terchange positions. In an Amceba moving toward the cathode the
extended protoplasm at the cathode end is gradually transferred to the
anode end, and as this change takes place it contracts. In the reaction
to light the protoplasm of the anterior end directed away from the light
is gradually transferred in the rolling movement to the lighted side; it
then contracts. It is therefore possible that in these cases also it is the
change from one condition to another that causes reaction.

It is notable that changes from one condition to another often cause
reaction when neither the first condition nor the second would, if acting
continuously, produce any such effect. Thus, Amcebe react negatively

_to tap water or to water from a foreign culture, but after transference to
such water they behave normally. Harrington and Leaming (1900)
show that when white light is thrown on an Amceba it ceases to move,
but if this light continues, the animal resumes movement. To constant
conditions Amoeba tends to become acclimatized.

But even constant conditions may induce reaction if they interfere
seriously with the life activities of the animal. Under great heat or
strong chemicals the protoplasm contracts irregularly and remains thus
contracted till death follows. A different example of the production of
a reaction by constant conditions is shown in the behavior of Amoebz
suspended in the water. Under these conditions, as we have seen, the
animal sends pseudopodia in all directions, taking a starlike form. It
is evident that the general condition of the organism, as well as an
external change, may determine a reaction.

The fact that the nature of the behavior depends on the general con-
dition of the organism is illustrated in another way by the observation
of Rhumbler, that Amcebe may begin to take food, then suddenly reject
it. This rejection occurs especially after subjection to light. Appar-
ently the light changes the condition of the animal in such a way that it
no longer reacts to food as it did.

In Ameeba, as in higher animals, the localization of the stimulation
partially determines the reaction. The sesult of stimulation on the
right side is to cause movement in a direction different from that pro-
duced by stimulation on the left side. In Amoeba the relation of the
movement to the localization of the stimulus is very simply determined,

THE BEHAVIOR OF AMGBA 2

through the fact that it is primarily the part stimulated that responds.
This part contracts or extends, thus partly determining the direction of
movement.

But the localization of the external stimulus is not the only factor in
determining the direction of locomotion. Especially in the negative
reactions certain other factors are evident, which are of much impor-
tance for understanding the behavior. After stimulation at one side or
end, the new pseudopodium is as a rule not sent out in a direction
exactly opposite that from which the stimulation comes. It usually ap-
pears, as we have seen, on some part of the original anterior end of the
body, and at first alters the course only slightly. This is evidently con-
nected with the fact that only the anterior end is attached to the sub-
stratum, and without such attachment locomotion cannot occur. If the
pseudopodium were sent out from the unattached posterior part of the
body, it would have to overcome the resistance of the contraction existing
there, and would have to find the substratum and become attached to it.
The new pseudopodium thus starts out from the region of least resist-
ance, and in such a way that the new movement forms a continuation
of the original one, though in a different direction. If the new direction
still leaves the anterior part of the body exposed to the action of the
stimulus, then a new pseudopodium is sent out in the same way, still
further altering the course. This: may continue till the original direc-
tion of locomotion is squarely reversed.

This is the method of changing the course that is usually seen in
the reactioris to mechanical (Fig. 9), chemical (Fig. 15), thermal, and
electric (Fig. 17) stimuli. From Davenport’s figures (Fig. 16) it ap-
pears to be likewise the method in the reactions to light.

From these facts it is clear that the direction of movement in a nega-
tive reaction is not determined entirely by the position of the stimulat-
ing agent or the part of the body on which it acts. The moving Amceba
is temporarily differentiated, having two ends of opposite character,
while the two sides differ from the ends. These internal factors play
a large part in determining the direction of movement; the present action
of Amoeba, even when responding to stimuli, depends, as a result of these
temporary differentiations, partly on its past action. The new pseu-
dopodium will be sent out under most circumstances from some part
of the anterior end, only under special conditions from a side, and still
more rarely from the posterior end. We have here the first traces of
relations which play large parts in the behavior of animals higher than
Amoeba. Structural differentiations have become permanent in most
animals, and as such play a most important réle in determining the
direction of movement. Further, in practically all animals the past

22 BEHAVIOR OF THE LOWER ORGANISMS

actions are, as in Amoeba, important factors in determining reactions
to present stimuli. In Amceba we see in the simplest way the effects of
past stimuli and past reactions in determining present behavior.

As a result of this interplay of external and internal factors in deter-
mining movement, the avoidance of a stimulating agent usually occurs
in Amoeba by a process which we should call in higher animals one of
trial. If the movement were directly and unequivocally determined by
the localization of the stimulus, there would be nothing involved that
could be compared to a trial. The direct withdrawal of the part stimu-
lated is a factor due immediately to the localization of the external agent.
But the sending forth of a pseudopodium in a new direction is not forced
by the external agent, but is an outflow of the internal energy of the
organism, and the position of this new pseudopodium is, as we have
seen, determined by internal conditions. The latter factors are those
which correspond to the activities that we call trial in higher animals.
If the new direction of movement leads to further stimulation, a new
trial is made. Such trials are repeated till either there is no further
stimulation, or if it is not possible to escape completely, until the stimu-
lation falls on the posterior end, and the animal is retreating directly
from the source of stimulation.

The entire reaction method may be summed up as follows: The
stimulus induces movement in various directions (as defined by internal
causes). One of these directions is then selected through the fact that
by subjecting the animal to new conditions, it relieves it from stimula-
tion. This is our first example of “selection from among the conditions
produced by varied movements,” — a phenomenon playing a large part,
as we shall see, in the behavior of organisms.

The method of reaction above described gives, with different stimuli,
two somewhat differing classes of results. In the reactions to mechani-
cal, chemical, and thermal stimuli, different directions are ‘‘tried”’ until
the organism is moving in such a direction that it is no longer subjected
to the stimulating agent; in this direction it continues to move. But in
the reactions to light and to electricity new directions are tried merely
until the stimulation falls upon the posterior end, and the organism is
retreating directly from the source of stimulation. There is no possibil-
ity of escaping the stimulating agent completely. In the reactions to the
two stimuli last mentioned the long axis of the animal must after a time
take up a definite orientation with respect to the direction from which
the stimulus comes, while in the reactions to other stimuli there is usually
no such orientation. This difference is due, not to any essentially dif-
ferent method of reacting in the two cases, but merely to the peculiar
distribution of the stimulating agents; light and electricity act continu-

THE BEHAVIOR OF AMGBA 23

ously, and always affect a certain side of the organism, while this is not
true of the other agents.

If an intense stimulus acts on the entire surface of Amceba at once,
the animal contracts irregularly and ceases to move. If the acting agent
is very powerful, the Amoeba may remain contracted till it dies; other-
wise it usually soon begins locomotion again.

We may classify the various changes in behavior due to stimulation
into three main types, which may be called the positive reaction, the
negative reaction, and the food reaction; these have already been de-
scribed in detail. These types are not stereotyped; each varies much
in details under different conditions. "The movements in these reactions
are clearly not the direct results of the simple physical action of the
agents inducing them (see Jennings, 1904 g). As in higher animals, so
in Ameeba, the reactions are indirect. The effect of external agents is
to cause internal alterations, and these determine the movements. It
is therefore not possible to predict the movements of the organism from
a knowledge of the direct physical changes produced in its substance by
the agent in question.

_ What decides whether the reaction to a given stimulus shall be posi-
tive or negative? ‘This question touches the fundamental problem of
behavior. The nature of the physical or chemical action of an agent
does not alone determine the reaction, for to the same agent opposite
reactions may be given, depending on its intensity, or upon various
attendant circumstances. If we should make a chemical or physical
classification of the agents affecting movement in Ameeba, this would
not coincide with a classification based on the reactions given. But the
agents which produce a negative reaction are in general those which
injure the organism in one way or another, while those inducing the
positive reaction are beneficial. Any agent which directly injures the
animal, such as strong chemicals, heat, mechanical impact, produces
the negative reaction. The positive reaction is known to be produced
only by agents which are beneficial to the organism. It aids the animal
to find solid objects on which it can move, and is the chief factor in
obtaining food. Thus the behavior of Amceba is directly adaptive; it
tends to preserve the life of the animal and to aid it in carrying on its
normal activities.

It may perhaps be maintained that certain reactions are not adap-
tive; for example, that to the electric current. The reaction in this case
does not tend to remove the organism from the action of the stimulat-
ing agent. But it is instructive to imagine in such a case an organism
with possibilities of high intelligence —say even a human being —
placed under similar conditions, with similar limitations of sense and

24 BEHAVIOR OF THE LOWER ORGANISMS

of locomotive power. Would it give a more adaptive reaction than
Amoeba? Evidently, the conditions are such that it is impossible for
the animal to escape by any means from the current. Since the stimu-
lation apparently comes most strongly from the anode side, it is natural
to move in the opposite direction. The method of the negative reaction
is that of a trial of certain directions of movement. This method is in
essence an adaptive one, and if it fails in the present case, certainly no
better course of action can be suggested.

Can the behavior of Amceba be resolved throughout into direct
unvarying reactions to simple stimuli, — into elements comparable to
simple reflexes ?

For most of the behavior described in the preceding pages the stimuli
can be recognized in simple chemical or physical changes in the environ-
ment. Yet there are certain trains of action for which such a resolution
into unvarying reactions to simple stimuli seems unsatisfactory. This
is notably true for some of the food reactions. In watching an Amceba
following a rolling food ball, as in Fig. 19, one seems to see the animal,
after failing to secure the food in one way, try another. Again, in the
pursuit of one Amceba by another, it is difficult to conceive each phase
of action of the pursuer to be completely determined by a simple present
stimulus. For example, in Fig. 21, after Amoeba } has escaped com-
pletely and is quite separate from Amoeba c, the latter reverses its
course and recaptures 6 (at 11-13). What determines the behavior of
c at this point? If we can imagine all the external physical and chemi-
cal conditions to remain the same, with the two Amcebe in the same
relative positions, but suppose at the same time that Amceba c has never
had the experience of possessing 8, — would its action be the same?
Would it reverse its movement, take in b, then return on its former
course? One who sees the behavior as it occurs can hardly resist the
conviction that the action at this point is partly determined by the
changes in ¢ due to the former possession of b, so that the behavior is
not purely reflex.

Of less interest than the case just mentioned are modifications in
behavior due to acclimatization, and to the interference of stimuli.
Amoeba may become accustomed to certain things, so as to cease reacting
after a time, though the condition remains the same. Thus Verworn
(1889 6) found that Amcebe which at first react to a weak electric cur-
rent may after a time continue their usual movements, without regard
to the current. Harrington and Leaming (1900), as we have seen, found
that white or blue light thrown on Amceba causes it to cease moving, but
if the light is continued, the movements begin again after a time. In-
deed, we have recognized above the general fact that change is the chief

THE BEHAVIOR OF AMGBA 25

factor:in causing reaction, so that such acclimatization is a constant,
normal factor in the behavior. A change in reaction due to a different
cause is seen in Rhumbler’s observation of the fact that Amoeba after
beginning to ingest food may reject it when subjected to light.

Beyond facts of this character, little is known as to the modifiability
of reactions in Amceba.

LITERATURE I

(Works are cited here by giving the author’s name followed by the date of publi-
cation. The full title will be found in the alphabetical list at the end of the volume.
Only the important works are mentioned.)

A. General account of the behavior of Ameeba, giving details of the observations
on which the foregoing account is mainly based : JENNINGS, 1904 é.

B. Attempted physical explanations of the activities of Amoeba: RHUMBLER,
1898 ; BUTSCHLI, 1892; BERNSTEIN, 1900; JENSEN, I90I, 1902; VERWORN, 1892;
JENNINGS, 1902 @, 1904 g; RHUMBLER, 1905.

C. General works on Ameba and its relatives: BUTSCHLI, 1880; PENARD, 1902;
LEIDY, 1879.

D. Reactions to unlocalized stimuli, and to localized heat: VERWORN, 1889.

£. Reaction to electricity: VERWORN, 1889 4, 1896 @; JENNINGS, 1904 é.

F. Reactions to light: DAVENPORT, 1897; HARRINGTON AND LEAMING, 1900;
ENGELMANN, 1879.

CHAPTER II
THE BEHAVIOR OF BACTERIA
I. STRUCTURE AND MOVEMENTS

BACTERIA are perhaps the lowest organisms having a definite form
and special organs for locomotion. In these characteristics they are less
simple than Amoeba and resemble higher animals, though in other ways
the bacteria are among the simplest of organisms. Whether they are
more nearly related to animals or to plants is a question of little impor-
tance for our purposes; they are usually considered as nearer to plants.

Bacteria are minute organisms living in immense numbers in decay-
ing organic matter, and found in smaller numbers almost everywhere.
They have characteristic definite
forms (Fig. 23); some are straight
cylindrical rods; some are curved
rods; some are spiral in. form;
others are spherical, oval, or of
other shapes. The individuals are
often united together in chains.

While some bacteria are quiet,
others move about rapidly. The
movements are produced by the

Fic. 23. — Different species of bacteria,
showing the distribution of the flagella. a,
Chromatium okeni, after Zopf; 6, Chro-
matium photometricum, after Engelmann ;
c, Spirillum undula, after Migula; d, Vibrio

swinging of whiplike protoplasmic
processes, the flagella or cilia. The
flagella may be borne singly or in
numbers at one end of the body,
or may be scattered over the entire

cholera, after Fischer; e, Bacilli of typhus,
after Fischer ; j, Bacillus syncyaneus, after
Fischer; g, Clostridium butyricum, after
Fischer.

surface. Figure 23 shows the dis-
tribution of flagella in a number
of species.

In most bacteria we can distinguish a permanent longitudinal axis,
and along this axis movement takes place. Thus both the form, and in
correspondence with it, the movement, are more definite than in Ameeba.
If the bacterium is quiet, we can predict that when it moves it will move
in the direction of this axis; for Amoeba such a prediction cannot be
26

THE BEHAVIOR OF BACTERIA 27

made. In some bacteria the two ends are similar, and movement may
take place in either direction. In others the two ends differ, one bearing
flagella, while the other does not. In these species the movement is still
further determined; the end bearing the flagella is anterior in the usual
locomotion. In none of the bacteria can we distinguish upper and lower
surfaces or right and left sides. As the bacterium swims, it revolves
continually on its long axis; the significance of this revolution will be
considered in our account of behavior in the infusoria.

2. REACTIONS TO STIMULI

The movements of the bacteria are not unordered, but are of such a
character as to bring about certain general results, some of which at
least are conducive to the welfare of the organism. If a bacterium
swimming in a certain direction comes against a solid object, it does
not remain obstinately pressing its anterior end against the object, but
moves in some other direction. If some strong chemical is diffusing in
a certain region, the bacteria keep out of this region (Fig. 24). They
often collect about bubbles of air, and about masses of decaying animal
or plant material. Often they gather about small green plants (Fig. 25),
and in some cases a large number of bacteria gather to form a well-
defined group without evident external cause.

How are such results brought about? ‘To answer this question, we
will examine carefully the behavior of the large and favorable form,
Spirillum’ (Fig. 23, c). Spirillum is a spiral rod, bearing a bunch of
flagella at one end. Ina thriving culture a large proportion of the indi-
viduals bear flagella at both ends and can swim indifferently in either
direction. It is said by good authorities that such specimens are pre-
paring to divide.

When Spirillum comes against an obstacle, it responds by the sim-
plest possible reaction, — by a reversal of the direction of movement.
In specimens with flagella at each end the new direction is continued
till a new stimulation causes a new reversal. In bacteria with flagella
at only one end, the movement backward is continued only a short time,
then the forward movement is resumed. Usually when the forward
movement is renewed, the path followed is not the same as the original
path, but forms an angle with it; the bacterium has thus turned to one
side. Whether this turning is due to currents in the water or other

1There are several species of Spirillum found in decaying organic matter. The species
have not been clearly determined in most of the work on behavior, and this is not of great
importance, as the behavior is essentially the same in character throughout.

28 BEHAVIOR OF THE LOWER ORGANISMS

accidental conditions, or, as is more probable, is determined in some way
by the structure of the organisms, has not been discovered. In the
infusoria, as we shall see, the latter is the case.

The reversal of movement of course carries the organism away from
the agent causing it. We find that the same reaction is produced when
the bacterium comes to a region where some repellent chemical is diffus-
ing in the water. This is well shown when a drop of } per cent NaCl is
introduced with a capillary pipette beneath the cover-glass of a prepara-
tion swarming with actively moving Spirilla. The bacteria at first keep
up their movement in all directions, but on coming to the edge of the
drop of salt solution the movement is reversed. Hence none of the bacteria
enter the drop, and it remains empty, like the chemicals in Fig. 24.

Fic. 24. — Repulsion of bacteria by chemicals. A. Repulsion of Chromatium weissii by
malic acid diffusing from a capillary tube. After Miyoshi (1897). B, Repulsion of Spirilla by
crystals of NaCl. a, Condition’ immediately after adding the crystals; } and ¢, later stages
in the reaction. After Massart (1891).

They react in this way toward solutions of most acids and alkalies, as
well as toward many salts and other chemicals. A drop of these chem-
icals remains entirely empty when introduced into a preparation of
Spirilla.

This simple reversal of movement is the method by which avoidance
of any agent takes place; in other words, it is the method of the nega-
tive reactions in bacteria. Bacteria also collect in certain regions, as we
have seen, — about air bubbles, green plants, food, etc.; they have
thus what are called ‘positive reactions’ as well as negative ones.
What is the behavior in the formation of such collections ?

One finds, rather unexpectedly, that the positive reaction is produced
in essentially the same way as the negative one, — by a simple reversal

THE BEHAVIOR OF BACTERIA 29

of movement under certain conditions. If we place water containing
many Spirilla on a slide, allowing some small air bubbles to remain be-
neath the cover-glass, we find after a time that the bacteria are collecting
about the bubbles. The course of events in forming the collections is
seen to be as follows: At first the Spirilla are scattered uniformly,
swimming in all directions. They pass close to the air bubble without
change in the movements. But gradually the oxygen throughout the
preparation becomes used up, while from the air bubble oxygen diffuses
into the water. After a time therefore the bubble must be conceived as
surrounded by a zone of water impregnated with oxygen. Now the bac-
teria begin to collect about the bubble. They do not change their direc-
tion of movement and swim straight toward the center of diffusion of
the oxygen. On the contrary the movement continues in all directions
as before. A Spirillum swimming close to the bubble into the oxygen-
ated zone does not at first change its movement in the least. It swims
across the zone until it reaches the other side, where it would again
pass out into the water containing no oxygen. Here the reaction oc-
curs; the organism reverses its movement and swims in the opposite
direction. If the specimen has flagella at each end, it continues its re-
versed movement until the opposite side of the area containing the oxygen
is reached; then the movement is reversed again. This is continued,
the direction of movement being reversed as often as the organism
comes to the outer boundary of the zone of oxygen within which it is swim-
ming.’ Thus the bacterium oscillates back and forth across the area of
oxygen. Specimens having flagella at but one end swim backward
only a short distance after reaching the boundary of the area, then start
forward again.

As a result of this way of acting the bacterium of course remains in
the oxygenated area. The latter thus retains every bacterium that
enters it. Many bacteria, swimming at random, enter the area in the
way described, react at the outer boundary, and remain; thus in the
course of time the area of oxygen swarms with the organisms, while
the surrounding regions are almost free from them. The finding of the
oxygen then depends upon the usual movements of the bacteria, — not
upon movements specially set in operation or directed by the oxygen.

Thus the positive and negative reactions of the bacteria are pro-
duced in the same way; both take place through the reversal of the
movement when stimulated. The stimulus is some change in the na-
ture of the surrounding medium. In the negative reaction the change
is from ordinary water to water containing some chemical; in the posi-

1 The bacterium may of course come against the bubble itself; the movement is then
reversed in the same way.

30

BEHAVIOR OF THE LOWER ORGANISMS

tive reaction it is the change from water containing oxygen to water con-

taining none.

Ja ay
9 ef = wm fae” * *,sewe
o«* ** ¢e . *. +" s*
” ° - ~. a el eese %%
be ep BP gbagete fest Meee ty
ae Se. a CAT IM e. € 9 at = aes bea b> &
Reese * Meets, § SS ee gr Dies Cb a
. . > “ve Pare
? > st.
ee °%, ; **

+° of .8. 8
2°? #e,

“fe
. eo of ty oo? $.°
oe * ee Ms a ot Ad
‘ ce “f; ote Este ~~

Fic. 25. — Collections of bacteria about algw, due to the oxygen produced by the latter.

A, Spirilla collected about a diatom.
green alga cell in the light.

After Verworn. 8B, Bacteria gathered about a spherical
a shows the condition immediately after placing the bacteria and

alga on a slide; no collection has yet formed. 06, Condition two minutes later; part of the bac-
teria have gathered closely about the cell. After Engelmann (1894).

Spirilla collect in the way above described about any source of oxy-

gen.

WNT
ae .

7
aot,
5
“ ats
’

8 lee
Spits Se
eves
. bated
‘
‘
.

Fic. 26. — An experi-
ment of Engelmann (1894),
showing that when a di-
atom is partly lighted, only
the part exposed to the
light produces oxygen.
The upper half of the di-
atom was in the shade, the
lower half in the light.
The bacteria have gathered
only about the lighted half
of the diatom.

Green plants give off oxygen in the light, so that the bacteria col-

lect about desmids, diatoms, and other microscopic
plants, in a lighted preparation, in the same way
as about air bubbles (Fig. 25). Many other bac-
teria react in the same way to oxygen; notably
the ordinary bacterium of decaying vegetable
infusions, Bacterium termo. Bacteria react to ex-
ceedingly minute quantities of oxygen, so that it
is possible to use them as tests for the presence of
small amounts of this substance. Engelmann
calculates that a bacterium may react to one one-
hundred-billionth of a milligram of oxygen. By
means of such reactions he has carried on investi-
gations to determine whether various green or col-
orless organisms do or do not give off oxygen;
results may be attained in this way that could
scarcely be reached otherwise (Fig. 26). Spirillum
(especially S. enue) is so remarkably sensitive to
oxygen that many individuals may react to the
oxygen produced by a single specimen of another
smaller bacterium (Engelmann).

When bacteria collect about bubbles or near
the edge of the cover-glass as a reaction to oxy-

THE BEHAVIOR OF BACTERIA 31

gen, certain differences are to be observed in different species. Spirilla
usually gather in a narrow zone a short distance from the air surface,
while Bacterium termo and most other species collect in another zone,
a little closer to the air. These relations are illustrated for Spirilla
and certain infusoria in Fig. 27. In such cases it is found that the
reversal of movement is
brought about in two differ-
ent regions. Passage from
the zone in which the quan-
tity of oxygen is adapted to
the particular species, to a
region having less oxygen,
causes the reversal; passage

toa region having more Oxy- Fic. 27. — Collections of Spirilla, a, and a ciliate in-
. fusorian Anophrys, 6, at the corner of the cover-glass,
Bt (next to the air surface) and about a bubble. Each remains in a narrow zone

causes the reversal with even a certain distance from the air surface, the bacteria
greater precision. As a re- farther away than the infusoria. After Massart.
sult, each species remains swimming about within the narrow zone
adapted to it, at a short distance from the air.

Thus any given species is adapted to a certain concentration of oxy-
gen, which may be called its optimum. Passage from the optimum in
either direction — toward more oxygen or less oxygen — causes the
reversal of movement, so that the
bacteria remain in the optimum.

Oxygen is of course necessary, or
at least useful, to these bacteria; most
of them become immobilized soon if
oxygen is excluded from the water.
The reversal of movement on passing
to a region of less oxygen is thus an
adaptive reaction. It is probable that
the concentration in which each spe-
cies tends to remain is that most
EES ee ea favorable to its life activities. Some
weissii in and about a capillary tube con- bacteria (the so-called anaérobic spe-
on alae ammonium nitrate. ¢jes) do not require oxygen, and these

bacteria do not collect in an oxygen-
ated area. One of these, Amylobacter, is known to avoid oxygen in
all effective concentrations; that is, it reverses its movement on com-
ing to a region containing oxygen (Rothert, 1gor).

Many bacteria collect in various other chemicals in the same manner
as in solutions of oxygen (see Fig. 28). Such collections are usually

fo--5

if
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\
%,

rte siictssredi elas tag,
>
® f{
tp RN
(po tes
f :

4, *

Bs ¥
yy asf

“Mesias

;
‘

32 BEHAVIOR OF THE LOWER ORGANISMS

formed in food substances; meat extract, for example, is an agent which
produces such collections in most species of bacteria. Pfeffer (1884)
found that Bacterium termo forms collections in meat extract, aspara-
gine, peptone, white of egg, conglutin, grass extract, leucin, urea, and
various other substances which might serve as nourishment. The
so-called sulphur bacteria use hydrogen sulphide in their nutritive pro-
cesses, and are found to collect in solutions of this substance (Miyoshi,
1897).

Many bacteria collect also in solutions of chemicals which probably
do not serve directly as food.’ Bacterium termo collects markedly in
weak solutions of potassium. carbonate, so that this is a favorable sub-
stance for demonstrating the collections. It collects also in most salts
of potassium, and in a less marked way in many other inorganic chem-
icals. Indeed, this species may be said to gather in weak solutions of
most inorganic chemicals, save in those of the powerful acids and alka-
lies. This bacterium lives on decaying vegetation, from which many
chemicals diffuse into the surrounding water; potassium salts especially
are given off in this manner. The tendency of the organisms to collect
in such salts therefore keeps them in proximity to the decaying vegeta-
tion which serves them as nourishment; these reactions are thus indi-
rectly adaptive. But Bacterium termo collects in certain chemicals that
are not thus given off by decaying vegetation. Pfeffer (1888) found that
they gather in salts of rubidium, cesium, lithium, strontium, and
barium, with which under natural conditions they never come in con-
tact. It has been suggested that this may be explained as due to a simi-
larity in the effect of these chemicals to the effects of others which they
do meet under natural conditions. The organisms react thus in the
same way to similar stimulation, without regard to its diverse source in
different cases. :

Many other bacteria resemble Bacterium termo in collecting in solu-
tions of a great variety of chemicals. Miyoshi (1897) found that the
sulphur bacterium Chromatium weissii forms collections in weak solu-
tions of hydrogen sulphide, potassium nitrate, ammonium nitrate (Fig.
28), calcium nitrate, sodium-potassium tartrate, ammonium phosphate,
monosodium phosphate, sodium chloride, cane sugar, grape sugar,
asparagine, and peptone.

Some reactions can hardly be considered in any way adaptive.
Rothert (1901) found that Amylobacter and another bacterium collect

1 The method of testing the reaction to chemicals has usually been as follows. A capillary
glass tube is filled with the solution to be tested, and one end is sealed. The open end is
then brought into the fluid containing bacteria ; these then enter the tube (Fig. 28) or leave
it empty (Fig. 24, A), depending on their reaction to the chemical.

THE BEHAVIOR OF BACTERIA 33.

in weak solutions of ether. From the method by which the gatherings
are produced, it is, of course, evident that collection in any agent signi-
fies merely that the organisms are less repelled by this agent than by
the surrounding conditions. All such collections are doubtless to be
’ conceived as brought about by a reversal of the movement on passing
from the dilute chemical to water containing none of the chemical. In
many cases this has been determined by direct observations ; * in other
cases the observations have not been made.

If the chemical is stronger, the reversal of movement is produced
when the bacteria come in contact with it, so that strong chemicals as
a rule remain empty. Thus the same chemicals that, when dilute, pro-
duce a “positive reaction”? cause, when stronger, a negative reaction.
All substances in dilute solutions of which Spirillum gathers are avoided
if stronger solutions are used. Miyoshi found this to be true also for
Chromatium weissii; and it is indeed a general rule for bacteria.

Why should the bacteria avoid strong solutions of the very substances
that when weak are “‘attractive”? It is, of course, well known that
strong solutions are as a rule injurious; the negative reaction is there-
fore distinctly adaptive under these conditions. Even when we can see
no use for the positive reaction, as in the case of the collecting of Amylo-
bacter in a solution of ether, we find that the reaction becomes negative
as soon as the solution becomes injurious. Amylobacter keeps out of
stronger solutions of ether.

Yet the bacteria are no more infallible in detecting i injurious sub-
stances than are higher organisms. If a poisonous chemical is mixed
with a solution in which the bacteria naturally collect, the organisms may
continue to*enter a drop of the solution, where they are killed. So
Pfeffer (1888, p. 628) found that if to an attractive solution of o.o1g per
cent potassium chloride be added 0.01 per cent mercuric chloride, Bac-
lterium termo and Spirillum undula continue to pass into the solution,
though they are there immediately killed. Bacterium termo swarms into
solutions of morphine (morphium chloride), where after ten minutes to
an hour all motion ceases.

To just what action of the strong solution is the repellent effect,
when it occurs, due? Strong solutions may be injurious from two dif-
ferent classes of causes. The specific properties of the given chemical
may cause injuries when acting intensely, and this might induce the
negative reaction. But farther, in any strong solution the osmotic press-
ure is high, and this produces injury in organisms by withdrawing the

1 The reversal of motion under these circumstances has been described especially by
Pfeffer (1884), Rothert (1901), and Jennings and Crosby (1901).
D

34 BEHAVIOR OF THE LOWER ORGANISMS

water from the protoplasm (plasmolysis). The reaction of bacteria
might then be due to this physical effect of strong solutions.

If the repellent effects of strong chemicals are due to their osmotic
pressure, then all solutions having equal osmotic pressure must be
equally repellent. This gives a method of testing the matter. Bacteria
have been subjected to the action of many chemicals in solutions of
equivalent osmotic pressure, with the following results. ‘There are many
strong chemicals which cause reaction when the osmotic pressure is very
low, — much lower than in the weakest solutions required to produce
reaction in other substances. Such are, as a rule, the strong mineral
acids and alkalies (Pfeffer); such are potassium cyanide, potassium
oxalate, sodium carbonate, sodium sulphite, and potassium nitrate in
the experiments of Massart (1889). The reactions produced by these
substances can be due then only to their chemical effects, without re-
gard to the osmotic pressure. On the other hand, Massart has shown
that in two species of bacteria — Spirillum undula and Bacterium me-
gatherium — the repellent power of a large number of chemicals is pro-
portional to the osmotic pressure of the solutions. It appears probable
therefore that the osmotic press-
ure is the cause of the reaction.*
In certain other bacteria it has
been demonstrated that there
is no such sensitiveness to os-
motic pressure. Bacterium termo
enters the strongest solutions of
attractive salts. This is sup-
posed to be because its proto-

Fic. 29. —Repulsion of Spirilla of sea water Plasm is permeable to the salts
by distilled water. The upper drop consists of in question. Taken all together,

sea water containing Spirilla; the lower of distilled :
water. At x these have just been united by a the experimental results demon-

narrow neck. At y and z the bacteria are driven te that in m es the
back before the advancing distilled water. After sae os . =: sae! —
Massart (1891). negative reaction is due to the

chemical properties of the sub-

stance, and they render it probable that in some other cases the reaction
is due to the osmotic pressure.

It is not always more concentrated solutions that cause the reversal

of movement. Bacteria that live in sea water keep out of areas of dis-

1 This conclusion is weakened by the fact that the bacteria are much less repelled by sev-
eral substances — glycerine, asparagine, dextrose, and saccharose— even when they are so
concentrated as to have higher osmotic pressure than the repellent solutions of the substances
above mentioned ( Massart, 1889). This is explicable only by making certain special, un-
proved assumptions for each case. The matter needs further investigation.

THE BEHAVIOR OF BACTERIA 35

tilled water in the same way (Fig. 29). This result may be due to the
fact that the osmotic pressure of the distilled water is less than that of
the sea water. On the other hand, it is possible that it is due merely to
the cessation of the chemical action of certain components of the sea
water. The case would then be comparable to the reaction induced
when bacteria come to a region containing no oxygen, as described in
the preceding pages.

Most bacteria do not react to light. But there are certain bacteria
for whose successful development light is required, and in these species
we find that reaction to light occurs in the same manner as the reaction
to oxygen in others. The species which react to light belong chiefly to
the group of sulphur bacteria. They contain a purple coloring matter
(bacterio-purpurin), which acts in a manner analogous to the chlorophyl
of higher plants. By its aid, through the agency of light, these bacteria
break up and assimilate carbon dioxide, giving off oxygen.

Engelmann (1882 a, 1888) made a thorough study of the relations to
light in one of these bacteria, Chromatium photometricum (Fig. 23, 6).
This organism moves actively and develops well in diffuse light, but in
the dark movement soon ceases and development stops. Only in the
light does it assimilate carbon dioxide and give off oxygen. In corre-
spondence with this, Chromatium photometricum collects in lighted areas.
This takes place in the same manner as the collection of bacteria in oxy-
gen. Engelmann placed the bacteria on a glass slide, in the usual way,
then illuminated a certain spot from below, while light was cut off from
the remainder of the preparation. He found that the bacteria do not
react on entering the lighted area. But when once within this area, on
coming to the outer boundary they suddenly reverse their movement
and swim backward a distance. Then they start forward again; on
coming anew to the boundary they react as before, and this happens
every time they reach the confines of the lighted area. ‘Thus none leave
the light; all those that enter the lighted area remain, and a dense col-
lection is soon formed here. In every detail the phenomena are parallel
to those found in the reactions of other bacteria to oxygen, as described in
previous pages.

A sudden decrease of light causes the same backward movement that
is observed when the bacteria come to the edge of the lighted area. If
the light is suddenly decreased by closing the diaphragm of the micro-
scope, all the bacteria at once swim backward a distance, — often ten
to twenty times their length. This shows that the reaction is not due
to the difference in illumination of two ends or two sides of the organism,
but only to the sudden decrease in light. This is shown also by the fact
that the bacteria may swim completely across the boundary of the lighted

36 BEHAVIOR OF THE LOWER ORGANISMS

region into the dark before reacting; the reaction then carries them
‘back into the light. With the smaller bacteria the reaction usually
occurs in this manner, while in larger species (Monas okeni; Ophido-
monas sanguinea) the reversal of movement occurs when only one end
has passed into the dark. A sudden increase of light merely causes the
organisms to swim forward a little more rapidly.

The purple bacteria are sensitive in different degrees to lights of dif-
ferent colors, tending to gather in certain colors more than in others.
This is shown in a most striking way when a spectrum is thrown on a
preparation of Chromatium photometricum (Fig. 30). The largest num-

a@BC D Eb F g

Fic. 30.— Distribution of bacteria in a microscopic spectrum. The largest group is in the
ultra-red, to the left; the next largest group in the yellow-orange, close to the line D. After
Engelmann.

ber of the bacteria collect in the ultra-red rays, which do not affect the
human eye at all. There is another collection in yellow-orange, while
a few are scattered through the green and blue. None are found in the
red, the violet, or ultra-violet. These collections arise in the same man-
ner as those in the white light. Bacteria swimming from blue toward
yellow-orange, or from red toward ultra-red, do not react at all, but con-
tinue their course. But specimens swimming in the opposite direction
react in the usual way, by leaping back, when they come to the outer
boundary of the ultra-red or the orange-yellow. Hence, in the course of
time, if the bacteria continue moving, almost all of them will be found
in the two regions last named.

It is a most interesting fact that the colors in which the bacteria col-
lect are exactly those which are most absorbed by them, and are also
those which are most favorable to their metabolic processes. Engel-
mann showed that most oxygen is given off, and hence that most carbon
dioxide is assimilated, in the ultra-red rays, while next to the ultra-red
the orange-yellow are most favorable to these processes. The reactions
of these bacteria to light are therefore adapted with remarkable preci-
sion to bringing them into regions which offer the best conditions for
their development. This is the more remarkable when we consider that

THE BEHAVIOR OF BACTERIA 37

under natural conditions the bacteria rarely if ever have opportunity
to react to the separated spectral colors.

Besides the purple bacteria, a green form, Bacterium chlorinum, is
known to assimilate carbon dioxide and to collect in light, in the same
manner as do the purple species.

The precise method by which bacteria react to heat and cold has
been little studied. Mast (1903) has shown that Spirilla do not react’
at all to changes in temperature. If a portion of the preparation con-
taining them is heated, they continue to pass into this region just as
before, though they may be at once killed by the heat. They may pass
also into a cold region, where motion gradually ceases.

The reaction to the electric current, like that to heat and cold, is in
need of a thorough examination. Verworn found that when subjected
to a continuous current some bacteria pass to the anode, others to the
cathode.

When placed in a vertical tube, some kinds of bacteria pass upward
to the top, in opposition to the force of gravity, while others gather at
the lower end (Massart, 1891). The factors on which this reaction to
gravity depends, and the precise way in which the reaction takes place,
are unknown,

Bacteria often react to contact with solids by settling down and
becoming quiet on the surface of the solid, which is usually some food
body. Bacterium termo thus forms dense collections on the surface of
such an object as a fly’s leg. aR

3. GENERAL FEATURES IN THE BEHAVIOR OF BACTERIA

We find that the chief reactions of bacteria, so far as they have been
precisely determined, take place through a single movement, — a tem-
porary reversal of the direction of swimming. This reaction is so simple
as to be comparable to a reflex action as we find it in an isolated muscle.
Whether the bacteria collect in a certain region or avoid it depends on
what it is that produces this reversal of movement. The reaction is
caused as a rule by a change in the environment of the organism. ‘This
change is usually brought about by the movement of the bacterium into
a region differing from that which it previously occupied, but it may be
due to an active alteration of the environment, as when light is suddenly
cut off. For the reaction to occur with the result of a general movement
of the organisms into a certain region, it is not necessary that different
parts of the body should be differently stimulated, as we found to be the
case in Amoeba. The only requirement for producing a general move-
ment of the organisms in a certain direction is that movement in any other

38 BEHAVIOR OF THE LOWER ORGANISMS

direction shall result in such a change as will produce the reversal of
movement. Not every change in the environment produces a reaction.
A change leading toward a certain optimum condition produces no reac-
tion, while a change of opposite character causes the reversal of move-
ment. A negative change in the environment — the decrease or cessa-
tion of action of a certain agent — may be as effective a stimulus as is
a positive change due to the entrance of a new agent into action. This
is well illustrated in the reactions to light and oxygen. All these rela-
tions we shall meet again, more fully illustrated, in the behavior of
infusoria.

The strength of the change necessary to cause a reaction has been
found by Pfeffer to vary in accordance with Weber’s law. This as usually
formulated expresses certain relations between sensation and stimulus
in man. According to this law, it is the relative change in the environ-
ment, not the absolute change, that causes a perceptible difference in
sensation. Thus if a certain perceptible weight x is pressing on the skin
of certain parts of the body, it requires an additional weight of about $ x
to produce a noticeable difference in the sensation; if the original weight
is 2 x, then an additional weight of $ x is required. In general the addi-
tional weight must be about one-third the original one before a notice-
able difference in sensation is produced. In the bacteria we know noth-
ing about sensations, but if we substitute reaction for sensation, similar
relations are found to hold good. Pfeffer found that if Bacterium termo
is cultivated in 0.01 per cent meat extract, they collect noticeably in capil-
lary tubes containing 0.05 per cent meat extract, but not in a weaker
solution. For producing reaction the inner fluid must therefore be five
times as strong as the outer. If now the culture fluid is raised to a
strength of 0.1 per cent meat extract, then five times this strength —
namely, 0.5 per cent — is required to induce the bacteria to collect. If
the culture fluid is 1 per cent, the fluid in the capillary tube must be
5 per cent in order to produce the usual reaction. The fluid in which the
bacteria collect must be always five times as strong as that in which
they live. It is the relative change, not the absolute change, that in-
duces reaction. This agreement between the relation of sensation to
stimulus in man and that of reaction to stimulus in these low organisms
is of great interest.

There is a considerable amount of variation in the reactions among
different individuals of the same species. Thus, Rothert found that
specimens of Amylobacter from a certain culture were markedly negative
to oxygen and positive to ether, while in specimens from another culture
these reactions were hardly observable. Even among individuals of the
same culture there is variation. Engelmann found that when the light

THE BEHAVIOR OF BACTERIA 39

falling on a group of individuals of Chromatium was suddenly decreased,
a few react to even very slight changes, a larger number to more consid-
erable changes, while some hardly react at all. “Nervous” and “apa-
thetic” individuals, Engelmann says, can be distinguished in any group.
Even in the same individual the reaction may vary. Engelmann found
that if the light was suddenly decreased, then restored, and at once de-
creased again, the bacteria usually do not react to the second decrease,
though they did to the first.

Among different kinds of bacteria there are, as we have seen, certain
constant differences in the reactions. A relation of great significance
becomes evident on examining the facts; behavior under stimulation
depends on the nature of the normal lije processes, — especially the meta-
bolic processes. Bacteria that require oxygen in their metabolism col-
lect in water containing oxygen; bacteria to which oxygen is useless or
harmful avoid oxygen. Bacteria that use hydrogen sulphide in their
metabolism gather in that substance. Bacteria that require light for
the proper performance of their metabolic processes gather in light,
while others do not. When one color is more favorable than others to
the metabolic processes the bacteria gather in that color, even though
they may under natural conditions have no experience .with separated
spectral colors. Keeping in mind that all these collections are formed
through the fact that the organisms reverse their movement at passing
out of the favorable conditions, these relations can be summed up as
follows: Behavior that results in interference with the normal metabolic
processes is changed, the movement being reversed, while behavior that
does not result in interference or that favors the metabolic processes is
continued.

This statement doubtless does not express the behavior completely,
yet the general fact which it sets forth is on the whole clearly evident.
The result of this method of action is to make the behavior regulatory,
or adaptive. Through it, the bacteria, like higher organisms, avoid
injurious conditions and collect in beneficial ones. There are some
exceptions to this; the adaptiveness is not perfect, as nothing is perfect
under ail conditions. The exceptions are perhaps not more numerous
in these lowest organisms than in the highest ones.

Putting all together, the behavior of the bacteria may be summed up
as follows: They swim about in a direction determined by the posi-
tion of the body axis, until the movement subjects them to an unfavora-
ble change; thereupon they reverse and swim in some other direction.
With rapid movements and much sensitiveness to unfavorable influ-
ences, this soon results in their finding and remaining in the favorable
regions. In the presence of a localized region of favorable conditions

40 BEHAVIOR OF THE LOWER ORGANISMS

(food or oxygen, for example) the organisms do not show movement in
a single direction, adapted to reaching these favorable conditions. On
the contrary, they show movements in all sorts of directions; one of
these is finally continued or selected by its success. We find again be-
havior based on the ‘“‘selection from among the conditions produced by
varied movements.”

' LITERATURE I
(On the behavior of Bacteria)
ENGELMANN, 1881, 1882 a, 1888, 1894; JENNINGS AND CROSBY, 1901 ; MASSART, ;

1889, 1891, 1891 @; MAST, 1903; MIYOSHI, 1897; PFEFFER, 1884, 1888; ROTHERT,
1901, 1903.

CHAPTER III
THE BEHAVIOR OF INFUSORIA; PARAMECIUM
STRUCTURE; MOVEMENTS; METHOD OF REACTION TO STIMULI

INTRODUCTORY

THE name Jnjusoria is applied to those unicellular organisms (aside
from bacteria) that swim by means of cilia or flagella, as well as to a few
others. The organs of locomotion are protoplasmic processes on the
body surface. Where these are short and numerous, they are called
cilia; where they are long and the organism bears but one or a small
number, they are called flagella. The organisms bearing cilia are
classed together as Ciliata; those with flagella are the Flagellata. Fig-
ure 31 shows a number of characteristic forms of the Ciliata. Along with
the infusoria we shall take up other unicellular organisms or develop-
mental stages that swim by means of such protoplasmic processes, —
for example, spermatozoa and swarm spores.

The infusoria are commonly found, as the name implies, in infusions
of decaying animal and vegetable matter. One of the commonest and best
known of the infusoria is Paramecium, found in water containing de-
caying marsh plants, or in hay infusion with which some marsh or pond
water has been mixed. The behavior of Paramecium has been studied
more than that of any other infusorian, so that we shall take this up
first as a representative of the group. The behavior of other species
will be then examined to discover how far the relations in Paramecium
are typical, and to bring out differences — especially points for which
Paramecium is not a favorable object of study.

1. BEHAVIOR OF PARAMECIUM; STRUCTURE

Paramecium (Fig. 32) is a whitish,:cigar-shaped animal, living in
immense numbers in decaying vegetable infusions, and visible to the
naked eye as a minute, elongated particle. The anterior part of the

41

42 BEHAVIOR OF THE LOWER ORGANISMS

body is slender but blunt, the posterior part thicker, but more pointed.
Thus the two ends differ, as in some bacteria, and there is a further

Fic. 31. — Examples of ciliate infusoria. «@, Spirostomum ambiguum Ehr., after Stein.
b, Stentor reselii Ehr., after Stein. c, Vorticella nebulifera O. F. M., after Biitschli. d, Col-
pidium colpoda Ehr., after Schewiakoff, from Biitschli. e, Loxophyllum meleagris O. F. M.,
after Biitschli. /, Stylonychia mytilus Ehr., after Engelmann.

differentiation of the lateral surfaces. One side, the oral surface, bears
a broad, oblique groove, known as the oral groove, or peristome, ex-

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 43
tending from the mouth in the middle of the body forward to the anterior
end. When the animal is placed with the oral surface below, the groove
extends from the right behind
toward the left in front (see Fig.
32). The animal is thus not bi-
laterally symmetrical, but slightly
spiral in form. The surface oppo-
site the oral groove is marked by
the presence near it of two large
contractile vacuoles; this may be
called the aboral surface. By con-
sidering the oral surface as ventral
we may distinguish for convenience
right and left sides. The entire
body is covered with fine cilia, set
in oblique rows. Those at the pos-
terior end are a little longer than
the others.

As to internal structure, we may
distinguish an outer firm layer
known as the ectosarc, enclosing
an inner fluid portion, the endo-
sarc. The ectosarc is covered by
a thin outer cuticle; below this it
is thickly set with rodlike sacs,
placed perpendicular to the surface
and known as trichocysts; the con-

tents of these may be discharged as
fine threads. The endosarc con-
tains two nuclei, the large macronu-
cleus and the minute micronucleus,
together with numerous masses of
food, most of them enclosed in
vacuoles of water. The endosarc

Fic. 32. — Paramecium, viewed from the
oral surface. L, left side; R, right side.
an., anus; ec., ectosarc; en., endosarc; }.v.,
food vacuoles; g, gullet; m, mouth; ma.,
macronucleus; mi., micronucleus; 0.g., oral
groove; P., -pellicle; ¢r., trichocyst layer.
The arrows show the direction of movement
of the food vacuoles.

is in continual movement, rotating lengthwise of the body, in the
direction shown by the arrows in Fig. 32. Between endosare and
ectosarc, but attached to the latter, are the two contractile vacuoles,
which at intervals collapse, emptying their contents to the outside.
From the mouth (m) a passageway the gullet (g), leads through the
ectosarc into the endosarc.

‘44 BEHAVIOR OF THE LOWER ORGANISMS

2. MOVEMENTS

Paramecium swims by the beating of its cilia. These are usually

YN Pe.
. es

Fic. 33. — Spiral path
of Paramecium. The fig-
/ures I, 2, 3, 4, etc., show the
successive positions occu-
pied. The dotted areas
with small arrows show the
currents of water drawn
from in front.

inclined backward, and their stroke then drives
the animal forward. They may at times be di-
rected forward; their stroke then drives the ani-
mal backward. The direction of their effective
stroke may indeed be varied in many ways, as
we shall see later. The stroke of the cilia is
always somewhat oblique, so that in addition to
its forward or backward movement Paramecium
rotates on its long axis. This rotation is over to
the left (Fig. 33), both when the animal is swim-
ming forward, and when it is swimming back-
ward. The revolution on the long axis is not
due to the oblique position of the oral groove, as
might be supposed, for if the animal is cut in
two, the posterior half, which has no oral groove,
continues to revolve.

The cilia in the oral groove beat more effec-
tively than those elsewhere. The result is to
turn the anterior end continually away from the
oral side, just as happens in a boat that is rowed
on one side more strongly than on the other.
As a result the animal would swim in circles,
turning continually toward the aboral side, but
for the fact that it rotates on its long axis.
Through the rotation the forward movement and
the swerving to one side are combined to pro-
duce a spiral course (Fig. 33). The swerving
when the oral side is to the left is to the right;
when the oral side is above, the body swerves_
downward; when the oral side is to the right the
body swerves to the left, etc. Hence the swerv-
ing in any given direction is compensated by an
equal swerving in the opposite direction; the re-
sultant is a spiral path having a straight axis.

The spiral course plays so important a part in the be-
havior of Paramecium that we must analyze it farther.
The spiral swimming is evidently the resultant of three
factors, — the forward movement, the rotation on the long

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 45

axis, and the swerving toward the aboral side. Each of these factors is due to a
certain peculiarity in the stroke of the cilia. The first results from the fact that the
cilia strike chiefly backward. The second is due to the fact that the cilia strike, not
directly backward, but obliquely to the right, causing the animal to rol] over to the
left. The third factor — the swerving toward the aboral side — is due largely to the
greater power of the stroke of the oral cilia, and the fact that they strike more nearly
directly backward. It seems partly due however to a peculiarity in the stroke of the
body cilia, by which on the whole they strike more strongly toward the oral groove
than away from it, thus driving the body in the opposite direction.

Each of these factors may vary in effectiveness, and the result is a change in the
movements. The forward course may cease completely, or be transformed into a
backward course, while the rotation and the swerving continue. Or the rotation
may become slower, while the
swerving to the aboral side ab
continues or increases; then
the spiral becomes much
wider. This result is brought

ab

Vs =iyt

direction of the beating of the
cilia to the left of the oral
groove; they beat now to the
left (toward the oral groove)
instead of to the right (Fig.
34). The result of this is, as
the figure shows, to oppose

ee
oe ‘
about by a change in the Fi
‘Sat Nera /
0

Fic. 34. — Diagrams of transverse sections of Parame-
cium, viewed from the posterior end, showing the change
in the beat of the cilia of the left side. a, Stroke of the
cilia in the usual forward movement. All the cilia strike
toward the right side (7), rotating the organism to the left

the rotation to the left, but
to increase the swerving
toward the aboral side. The
width of the spiral, or the final
complete cessation of the rota-
tion on the long axis which sometimes occurs, depends on the number and effective-
ness of these cilia of the left side that beat toward the oral groove instead of away
from it. A large part of the behavior of Paramecium depends, as we shall see, on
the variations in the three factors which produce the spiral course.

(2), as shown by the arrows. 3, Stroke of the cilia after
stimulation. The cilia of the left side strike to the left,
opposing the lateral effect of the cilia of the right side.
This causes the animal to cease revolving, and to swerve
toward the aboral side (ab). 0, Oral groove.

3. ADAPTIVENESS OF THE MOVEMENTS

How does Paramecium meet the conditions of the environment ?
Under the answer to this question must be included certain aspects of
the spiral movement, described in the foregoing paragraphs. The
problem solved by the spiral path is as follows: How is an unsym-
metrical organism, without eyes or other sense organs that may guide it
by the position of objects at a distance, to maintain a definite course
through the trackless water, where it may vary from the path to the right
or to the left, or up or down, or in any intermediate direction? It is
well known that man does not succeed in maintaining a course under

46 BEHAVIOR OF THE LOWER ORGANISMS

similar but simpler conditions. On the trackless snow-covered prairie
the traveller wanders in circles, try hard as he may to maintain a straight
course, — though it is possible to err only to the right or left, not up or
down, as in the water. Paramecium meets this difficulty most effec-
tively by revolution on the axis of progression, so that the wandering
from the course in any given direction is exactly compensated by an
equal wandering in the opposite direction. Rotation on the long axis
is a device which we find very generally among the smaller water or-
ganisms for enabling an unsymmetrical animal to follow a straight
course. The device is marvellously effective, since it compensates with
absolute precision for any tendency or combination of tendencies to
deviate from a straight course in any direction whatsoever.

The normal movements of Paramecium are adaptive in another
respect. The same movements of the cilia which carry the animal
through the water also bring it its food. The oral cilia cause a current
of water to flow rapidly along the oral groove (Fig. 33). In the water
are the bacteria upon which Paramecium feeds; they are carried by
this current directly to the mouth. In the gullet is a vibrating membrane
which carries particles inward; the bacteria which reach the mouth
are thus carried through the gullet to the endosarc, where they form
food vacuoles and are digested.

Not only food, but also other substances, may be brought to Para-
mecium by the currents due to the movements of the cilia. It is im-
portant for understand-
ing the behavior of this
animal to realize that
not only does it move
; forward to meet the en-
: vironment, but the en-
vironment, so far as that
is possible, also streams
backward to meet it.
If there is a chemical
diffusing in the water in

_ Fic. 35. — Paramecium approaching a region contain- front of it, or if the water
ing India ink (shown by the dots). The India ink is drawn is warmer or colder, or
out to the anterior end and oral groove of the animal. a = :

differs in any other way,

a sample of this differentiated region is pulled backward in the form
of a cone, and as a result of the stronger beating of the oral cilia,
passes as a stream down the oral groove to the mouth (Fig. 33). This
may best be seen by bringing near the anterior end of a resting Parame-
cium, by means of a capillary pipette, some colored solution, such as

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 47

methyline blue, or by using in the same way water containing India
ink. Or if a cloud of India ink, with a definite boundary, is produced
in the water containing swimming Paramecia, a cone of the ink is seen
to move out to meet the advancing animals (Fig. 35). Thus Parame-
cium is continually receiving “samples” of the water in front of it.
Since in its spiral course the organism is successively pointed in many
different directions, the samples of water it receives likewise come suc-
cessively from many directions (Fig. 33). Thus the animal is given
opportunity to “try” the various different conditions supplied by the
neighboring environment. Paramecium does not passively wait for
the environment to act upon it, as Amoeba may be said, in com-
parison, to do. On the contrary, it actively intervenes, determining
for itself what portion of the environment shall act upon it, and in
what part of its body it shall be primarily affected by the varying con-
ditions of the surrounding water. By thus receiving samples of the
environment for a certain distance in advance, it is enabled to react
with reference to any new condition which it is approaching, before it
has actually entered these conditions.

4. REACTIONS TO STIMULI

Let us suppose that as Paramecium swims forward in the way just
described, it receives from in front a sample that acts as a stimulus, —
that is perhaps injurious. The ciliary current brings to its anterior
end water that is hotter or colder than usual, or that contains some
strong chemical in solution, or holds large solid bodies in suspension, or
the infusorian strikes with its anterior end against a solid object. What
is to be done?

Paramecium has a simple reaction method for meeting all such
conditions. It first swims backward, at the same time necessarily
reversing the ciliary current. It thus gets rid of the stimulating agent,
— itself backing out of the region where this agent is found, while it
drives away the stimulus in its reversed ciliary current. It then turns
to one side and swims forward in a new direction. The reaction is
illustrated in Fig. 36. The animal may thus avoid the stimulating
agent. If, however, the new path leads again toward the region from
which the stimulus comes, the animal reacts in the same way as at first,
till it finally becomes directed elsewhere. We may for convenience
call this reaction, by which the animal avoids all sorts of agents, the
“avoiding reaction.” :

In the foregoing paragraph we have given only a general outline of
the behavior. The avoiding reaction has certain additional features,

48 BEHAVIOR OF THE LOWER ORGANISMS

which add greatly to its effectiveness. After getting rid of the stimulus
by swimming backward a distance there must be some way of deter-

Fic. 36. — Diagram of the avoiding reaction of Paramecium. A is a solid object or other
source of stimulation. 1-6, successive positions occupied by the animal. (The rotation on the
long axis is not shown.)

mining the new direction in which the animal is to swim forward. It
is evident that some method of testing the conditions in various different
directions in advance would be the most effective way of accomplishing
this. The infusorian now moves in precisely such a way as to make
such tests. It will be recalled that in its usual course the animal is
revolving on the long axis and swerving a little toward the aboral side
(Fig. 33), so that it swims in a narrow spiral. After swimming back-
ward a certain distance in response to stimulation, the revolution on the
long axis becomes slower, while the swerving toward the aboral side is
increased. As a result the anterior end swings about in a large circle;
the animal becomes pointed successively in many different directions,
as illustrated in Figs. 37 and 38. From each of these directions it
receives in its ciliary vortex a “sample” of the water from immediately
in advance, as the figures show. As long.as the samples contain the
stimulating agent, — the hot or cold water, the chemical, or the like, —
the animal holds back and continues to swing its anterior end in a
circle — “trying” successively many different directions. When the
sample from a certain direction no longer contains the stimulating agent,
the animal simply resumes its forward course in that direction. Thus
its path has been changed, so that it does not enter the region of the
chemical or the hot or cold water. Mechanical obstacles are avoided
in precisely the same way, save that of course the ciliary vortex does
not bring samples of the stimulating agent, so that the infusorian is
compelled to try starting forward repeatedly in various directions, be-
fore it finds one in which it can pass freely.

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 49

This method of behaving is perhaps as effective a plan for meeting
all sorts of conditions as could be devised for so simple a creature. On
getting into difficulties the animal retraces its course for a distance,
then tries going ahead in various directions, till it finds one in which
there is no further obstacle to its progress. In this direction it continues.
Through systematically testing the surroundings, by swinging the an-
terior end in a circle, and through performing the entire reaction re-
peatedly, the infusorian is bound in time to find any existing egress from
the difficulties, even though it be but a narrow and tortuous passageway.

The different phases of this avoiding reaction are evidently due to modifications
of the three factors in the spiral course. ‘The swimming backward is due of course
to a reversal of the forward stroke of the cilia. The turning toward the aboral side
is an accentuation of the swerving that takes pla¢e always; it is due to the fact that
the cilia at the left side of the body strike during the reaction toward the oral groove
instead of away from it. Thus the cilia of both right and left sides now tend to turn
the animal toward the aboral side. The difference between the usual condition and
that found during the reaction is illustrated in Fig. 34. Finally, the decrease or
cessation in the revolution on the long axis is due to the same factor as the increase
in swerving toward the aboral side. During the reaction the cilia of the left side
oppose the usual revolution on the long axis to the left (as shown in Fig. 34),
through the same change which causes them to assist in turning the body toward the
aboral side.

_ The avoiding reaction varies greatly under different conditions,
though its characteristic features are maintained throughout. But its
different phases vary in intensity depending
on circumstances. The backward movement
may be long continued, or may last but a
short time; or there may be merely a stop-
page or slowing of the forward movement.
The swerving toward the aboral side may be
only slightly increased, while the revolution
on the long axis becomes a little slower. In
this case the anterior end swings about in
a small circle, as in Fig. 37, so that the ani-
mal is pointed successively in a number of
directions varying only a little from the origi-
nal one. Witha stronger stimulus the swerv-
ing toward the aboral side is more decided,

Fic. 37. — Paramecium
: a rete swinging its anterior end about in
while the rotation on the long axis is slower; a small circle, in a weak avoiding

reaction. 1, 2, 3, 4, successive

then the anterior end swings about a larger poulibeacocapled:

circle, as in Fig. 38. The Paramecium thus

becomes pointed successively in many directions differing much from

the original one. Finally, the rotation on the long axis may com-
E

5° BEHAVIOR OF THE LOWER ORGANISMS

pletely cease, while the swerving toward the aboral side is farther
increased; then the Paramecium swings its anterior end about a circle
with its posterior
end near thecen-
tre (Fig. 39). In
this case the
animal may turn
directly away
from the stimu-
lating agent.
Such _ varia-
tions are seen
when the infu-
soria are sub-
jected to stimuli
of different in-
tensities. If the
animals come in contact with any strong chemical, or with water that is
very hot, they respond first by swimming a long way backward, thus
removing themselves as far as
possible from the source of
stimulation. Then they turn
directly toward the aboral
side, —the rotation on the
long axis completely ceasing,
as in Fig. 39. In this way the
animal may turn directly away
from the drop and retrace its
course. But often the reac-
tion is so violent that the an-
terior end swings about in two
or three complete circles before
the animal starts forward
again. Then the new path
may lead it again toward the

Fic. 38. — More pronounced avoiding reaction. The anterior end
swings about a larger circle. 1-5, successive positions occupied.

. ‘ Fic. 39. — Avoiding reaction when revolution on

drop, when the reaction is the long axis ceases completely. The anterior end

repeated. swings about a circle of which the body forms one of
the radii.

In marked contrast with
this violent reaction is the behavior when the stimulus is very weak.
A weak stimulus is produced for example by 345 per cent to 45 per
cent sodium chloride, or by water only three or four degrees above the
normal temperature. The Paramecium whose oral cilia bring it a

THE BEHAVIOR OF INFUSORIA,; PARAMECIUM 51

sample of such water merely stops, or progresses more slowly, and
begins to swing its anterior end about in a circle, as in Fig. 37, thus
“trying” a number of different directions. As long as the oral cilia
continue to bring it the weak salt solution or the warmed water, the
animal holds back, and continues to swing its anterior end about ina
circle. When the anterior end is finally pointed in a direction from
which no more of the stimulating agent comes, the Paramecium
swims forward. The reaction in this case is a very precise and delicate
one; in a cursory view the animal seems to turn directly away from
the region of the stimulus, — the revolution on the long axis and swing-
ing of the anterior end in a circle being easily overlooked. :

Between this delicate reaction and the violent one first described
there exists every intermediate gradation, depending on the intensity of
the stimulation.

Paramecia react to most of the different classes of stimuli which act
upon them, in the way just described. Mechanical stimuli, such as
solid obstacles, or disturbances in the water; chemicals of all sorts;
heat and cold; light that is sufficiently powerful to be injurious; electric
shocks, and certain disturbances induced by gravity and by centrifugal
force, all cause the animal to respond by the avoiding reaction, so that
it escapes if possible from the region or condition that acts as a stimulus.
Certain peculiarities and special features in the action of the different
classes of stimuli will be taken up separately in the following chapters.

Stimulating agents produce the same reaction when they act on the
entire surface of the body as they do when they reach only the anterior
end or oral groove. This is shown by dropping the animals directly
into a 4 per cent solution of sodium chloride, or into corresponding
solutions of other chemicals; or into hot or cold water. They at once
give the avoiding reaction; they swim backward, turn toward the aboral
side, then swim forward, and this reaction may be repeated many times.
If the stimulating agent is not so powerful as to be directly destructive,
the reaction ceases after a time, and the Paramecia swim about within
the solution as they did before in water.

This experiment shows clearly that the cause of the avoiding reaction
does not lie in the difference in the intensity of the chemical on the two
sides or two ends of the animal, as is sometimes held. For as we have
just seen, the animal reacts in the same way when the entire surface of
the body is subjected equally to the action of the chemical or the changed
temperature. It is clear that the cause of the reaction is the change
from one solution or temperature to another. This is evident further
from the fact that the animal reacts as a rule when the change occurs,
but ceases to react after the change is completed. To constant con-

52 BEHAVIOR OF THE LOWER ORGANISMS

ditions Paramecium soon becomes acclimatized; it is change that
causes reaction.

To this general statement there are certain exceptions. If we place
the infusoria in conditions of such intense action that they are quickly
destructive, —for example, in 2 per cent potassium bichromate, or
in water heated to 38 degrees C., —the animals continue to react till they
die. For two or three minutes they rapidly alternate swimming back-
ward with turning toward the aboral side and swimming forward,
till death puts an end to their activity. Thus very injurious conditions
may produce reaction independently of change. But as a general rule,
it is some change in the conditions that causes the animal to change its
behavior. The animal, having been subjected to certain conditions,
becomes now subjected to others, and it is the transition from one state
to another that is the cause of reaction. This is a fact of fundamental
significance for understanding the behavior of lower organisms.

But it is not mere change, taken by itself, that causes reaction, but
change im a certain direction. This is shown by observation of the
behavior of the individuals as they pass from one set of conditions to
another. If we place Paramecia on a slide in ordinary water, then in-
troduce into the preparation, by means of a capillary pipette, a drop of
4 per cent sodium chloride, as shown in Fig. 40, we find that the
animals react at the change from the water to the salt solution, so that
they do not enter the latter. If, on the other hand, the animals are first
mixed with + per cent salt solution, and a drop of water is introduced
into the preparation (as in Fig. 40), they do not react at passing from the
salt solution to the water. In the same way, Paramecia at a temperature
of 30 degrees react at passing to a higher temperature, but not at passing
to a lower temperature. Paramecia at 20 degrees, on the other hand,
react at passing to a lower temperature, not at passing to a higher. To
these relations we shall return.

A relation which is worthy of special emphasis is the following: The
direction toward which the animal turns in the avoiding reaction does
not depend on the side of the animal that is stimulated, but is deter-
mined by internal relations. The animal always turns toward the aboral
side. It is true that with chemical stimuli the stimulation usually
occurs on the oral side, so that the animal turns away from the side
stimulated. But, as we have just seen, it turns in the same way when
all parts of the body are equally affected by the stimulating agent.
Furthermore, it is possible to apply mechanical stimuli to various parts
of the body, and observe the resulting reaction. If with the tip of a fine
glass point we touch the oral side of Paramecium, the infusorian turns
directly away from the point touched. But if we touch the aboral side,

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 53

the Paramecium turns in the same manner as before, — toward the
aboral side, and hence toward the point touched. This experiment is
more easily performed, and the results are more striking, with certain
of the Hypotricha,* because these animals do not continually revolve on
the long axis, as Paramecium does.

The general effect of the avoiding reaction is to cause the animals
to avoid and escape from the region in which the stimulus is acting.
This may be illustrated for the different classes of stimuli in the follow-
ing ways.

The effects of this reaction to chemicals may best be seen by intro-
ducing a little $ per cent solution of sodium chloride into the water
containing the ani-
mals. For this pur-
pose water with many
Paramecia is placed
on a slide and covered
with a long cover-
glass supported near
its end by glass rods.
A medicine dropper
is drawn to a long,

slender point, and with : tency uP ees pe oe
. 1G. 40. — Method of introducing a chemical into a slide

this a drop of the salt o¢ infusoria.

solution is introduced

beneath the cover-glass, as illustrated in Fig. 40. The Paramecia are
swimming about in all directions, but as soon as they come to the
= —_—__—_—_——_——, region of the salt solution, the
De aS oa By ||.| avoiding reaction is given in the
ten A Se as ot os) way already. desenbed,: ~and
ia eof ‘-:.* ‘| the animals swim elsewhere.
“Hoe ete eet. > sf] Thus the drop of salt solution
Ate tt ts te 4 emeins empty (Pig aa
SERCO Ree Rae etre Practically all strong chemicals
Fic. 4t. — Slide of Paramecia four minutes induce the avoiding reaction, so
after, the introduction of a drop of 4 per cent that Paramecia do not enter them.
NaCl. The drop remains empty. This has been shown for many
alkalies, neutral salts, and organic substances, and for strong acids.
In the case of acids the reaction differs in certain respects from the
behavior under the influence of other chemicals; this will be brought
out later.

The reaction to heat or cold may easily be shown by placing a drop

1See Chapter VII.

54 BEHAVIOR OF THE LOWER ORGANISMS

of hot or cold water on the cover-glass of a slide of Paramecia, or by
touching the cover-glass with a hot wire, or a piece of ice. The animals
respond by the avoiding reaction, just as when stimulated by a chemical,
so that the hot or cold region remains vacant. The intensity of the re-
action depends on the temperature, and very hot water causes a much
more decided reaction than very cold water.

The avoiding reaction is seen under mechanical stimulation when a
specimen in swimming comes against an obstacle. It may also be shown
by touching the anterior end of the animal with a fine glass point. A
slight disturbance in the water may be induced by injecting a fine
stream of water against the animal with a pipette drawn to a capillary
point; the animal then responds by the avoiding reaction, thus swimming
elsewhere.

Special features in the reactions to various different classes of stimuli
will be dealt with in the next chapter.

5. “ PositIvE REACTIONS ”

The reactions thus far described have the effect of removing the
animal from the source of stimulation; they might therefore be charac-
terized as negative. But Paramecia are known also to collect in certain
regions, giving rise to what are commonly known as positive reactions.
How are these brought about ?

A simple experiment throws much light on the cause of such col-
lections. Under usual conditions the animals avoid a 345 per cent solu-
tion of NaCl, so that when a drop of this is introduced into a slide of
Paramecia, they leave it empty. But if we mix the animals with $ per
cent NaCl, then introduce into a slide of this mixture a drop of
qo per cent NaCl, in the way shown in Fig. 40, we find that the Para-
mecia quickly collect in this drop, though under ordinary circumstances
they avoid it. Very soon the drop of 345 per cent NaCl is swarming with
the infusoria, as in Fig. 43, while very few remain in other parts
of the preparation. The phenomena are identical with what has often
been called positive chemotaxis.

Careful observation of the movements of the individuals shows,
as might be expected, that the Paramecia collect in the 345 per cent NaCl
merely because they avoid the stronger solution more decidedly. Pas-
sage from the +4, per cent solution to the } per cent solution causes the
avoiding reaction, while passage in the reverse direction does not. The
details of the behavior are as follows: The Paramecia in the 4 per cent
NaCl are swimming rapidly in all directions, so that many of them are
carried toward the drop. On reaching its boundary they do not react

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 55

in any way, but swim directly into it. They continue across till they
reach the farther boundary, where they come in contact again with the
4 per cent solution. Here the reaction occurs. The animals give
the avoiding reaction, swimming backward, turning toward the aboral
side, and starting forward again, etc. They of course soon come in
contact again with the outlying 4 per cent NaCl, whereupon they react
as before, and this continues, so that they do not leave the drop of 45 per
cent NaCl. The path of a single Paramecium in such a drop is like
nat shown in Fig. 44. Since all the infusoria that enter the drop of

Zo per cent NaCl remain, it soon swarms with them.

fe place of NaCl, we may use pairs of solutions of other chemicals,
one stronger than the other, — taking pains of course not to employ
concentrations that are decidedly injurious. With any of the ordinary
inorganic salts or alkalies the animals collect in the weaker solution,
through the fact that they avoid the stronger one in the way described
above. The same concentration of a given chemical may play opposite
réles in successive experiments, depending on whether it is associated
with a weaker or a stronger solution. In the former case the Paramecia
avoid it; in the latter they gather within it. If the weaker solution sur-
rounds a drop of the stronger, the latter is left empty, and the Para-
mecia remain scattered through the preparation, as in Fig. 41. If
the stronger solution surrounds the weaker, the latter becomes filled
with the Paramecia, as in Fig. 43, while the former is left nearly
empty. Thus with the same pair of substances we get either a dense
aggregation (or what is often called positive chemotaxis), or a certain
area left vacant (“negative chemotaxis”), depending on the relation
of the two fluids to each other.

If we use pure water in place of the weaker solution, we get the same
result; the Paramecia collect in the drop of water. This is easily shown
by introducing a drop of water into a preparation of Paramecia that have
been mixed with } per cent NaCl; the water soon swarms with the in-
fusoria. The culture water in which Paramecia live usually contains
various salts, and is often alkaline in reaction. If a drop of distilled
water is added (as in Fig. 40) to a preparation of infusoria in such
culture water, the animals gather in the distilled water.

The same results may be obtained with water of differing tempera-
tures. This is done by surrounding an area of water at the normal
temperature with water at a temperature considerably higher or lower.
The Paramecia may be placed on a slide in the usual way, with a cover-
glass supported by glass rods. This slide is then placed on a bottle
or other vessel containing water heated to forty-five or fifty degrees.
As soon as the Paramecia begin to move about more rapidly in conse-

56 BEHAVIOR OF THE LOWER ORGANISMS

quence of the heat, a drop of cold water is placed on the upper surface
of the cover-glass. At once a dense collection of Paramecia is formed
beneath it (Fig. 42). Observation of
: . the movements of the individuals
Faget shows that this collection is formed in
ie. si? palais +- @ the same way as the collections pro-
TES ieee ane duced in chemicals (Figs. 43, 44,
ce : ' etc.). The Paramecia at a distance

Fic. 42. —A slide of Paramecia is from the cooled region do not turn
heated to 40 or 45 degrees, then adrop of gnd swim directly toward it. But the
cold water (represented by the outline a) . . - S :
is placed on the upper surface of the Paramecia are swimming rapidly in
cover-glass. The animals collect beneath aj] directions, and many enter every
eee instant the region beneath the drop.
They do not react on entering, but on reaching the opposite side, where
they would pass out again into the heated water, they give the avoid-
ing reaction. This is repeated every time they come to the other
boundary of the drop, so that
the path of an individual within | - ‘ ‘
the cooled region is similar to that
shown in Fig. 44. Every Para-
mecium that enters the cooled .
region therefore remains, and | - $
soon a dense swarm is formed. ; - fee :

A collection may be formed in
the same way by resting the slide age Eo caiperogtet bes Pekin abe
of Paramecia on a piece of ice and
placing a drop of warmed water on the upper surface; the Paramecia
now collect in the warmed region. But the collection is never so pro-
nounced as in the experiment last described, because the Paramecia
when cooled move less rapidly.

Thus the Paramecia collect in certain regions because they give
the avoiding reaction when passing from certain conditions to others,
while when passing in the reverse direction they do not. Paramecia
at the normal temperature give the reaction at passing both to hotter
and to colder water; they therefore tend to gather in water at the usual
temperature. This temperature at which they gather may be spoken
of as the optimum. Passage away from the optimum induces the
avoiding reaction; passage toward the optimum does not.

In the case of the chemicals thus far considered, the animals give
the reaction at passing from the weaker to the stronger solution, not at
passing in the opposite direction, so that they collect in the weaker solu-
tion. The optimum for these substances is thus zero, and this natu-

.

THE BEHAVIOR OF INFUSORIA,; PARAMECIUM 57

rally results in the tendency of the animals to collect in distilled water.
But there are certain chemicals of which the optimum is a certain posi-
tive concentration, so that Paramecia give
the avoiding reaction at passing to weaker
solutions or to water containing none of
the substance in question. This is the
case with acids and with oxygen. If a
drop of very weak acid is introduced into 7
a slide of Paramecia (Fig. 43) that are in
ordinary water, the animals quickly gather
in the drop. This may be shown by the
use of about +45 to 45 per cent of the ordi-
nary laboratory solutions of hydrochloric
or sulphuric acid, or of #5 to x per cent ‘Fic. 44.— Path followed by a
acetic acid. In a dict" time the - drop is “Sau LRARet aie ee
swarming with Paramecia.*

Observation shows that the method of collecting in the acid is the
same as in the cases before described. The rapid movements of the
animals in all directions are what carry them into the drop. They do
not react in any way at the moment of entering it, but swim across.
At the point where they would pass out into the surrounding water they
respond by the avoiding reaction; hence they return to the acid. This
is repeated each time that they come to the boundary. Hence all that
enter the acid remain till it is crowded. The path of a single Parame-
cium within a drop of acid is shown in Fig. 44.

In the formation: of all these collections the natural roving move-
ments play an essential part. These movements cause any given speci-
men in the course of a short time to cross almost any given area in the
preparation, and hence bring the animals to the introduced drop. The
animals do not turn and swim in radial lines toward the drop of acid.
If a ring is marked on the upper surface of the cover-glass, as many
Paramecia will be found to pass beneath this ring before a drop of acid
is placed beneath it as after. But in the latter case all that pass beneath
the ring remain, and the collection results. If we wait, before introduc-
ing the acid, till all have become nearly quiet, no collection is produced.

We may sum up the usual behavior of Paramecium under the vari-
ous stimuli of the environment in the following way. The natural
condition of the animal is movement. In constant external conditions
(unless destructive) the movements are not changed, — that is, there

1In all these experiments it is assumed, of course, that the preparation contains the
infusoria in very large numbers. With scattered specimens only, the results are slow and
not striking.

58 ._ BEHAVIOR OF THE LOWER ORGANISMS

is no reaction, — even though these conditions do not represent the
optimum. But as its movements carry the animal from one region to
another, the environmental conditions affecting it are of course changed,
and some of these changes in condition act as stimuli, causing the ani-
mal to change its movements. If the environmental change leads
toward the optimum, there is no reaction, but the existing behavior is
continued. To a change leading away from the optimum (in either a
plus or minus direction), Paramecium responds by the “avoiding reac-
tion.”” This consists essentially in a return to a previous position,
through a backward movement, then in “trying” different directions of
movement till one is found which leads toward the optimum. Ex-
pressed in a purely objective way, the animal performs movements
which subject it successively to many different environmental condi-
tions. As soon as one of the conditions thus reached is of such a char-
acter as to remove the cause of stimulation, the avoiding reaction ceases
and the infusorian continues in the condition now existing. This
method of reacting causes the animals to collect in certain regions (as
near the optimum as possible), and to avoid other regions. ‘Thus are
produced the so-called positive and negative reactions. The behavior
may be characterized briefly as a selection from the environmental con-
ditions resulting from varied movements.

Some details of the behavior under the different classes of stimuli
will be given in the next chapter.

LITERATURE If

On the character of the movements and reactions of Paramecium: JENNINGS
1904 4, 1899, 1901.

CHAPTER IV

BEHAVIOR OF PARAMECIUM (Continued)

SPECIAL FEATURES OF THE REACTIONS TO A NUMBER OF DIFFER-
ENT CLASSES OF STIMULI

In the preceding chapter the general method of the reactions of
Paramecium to most classes of stimuli has been described. In the
present chapter certain important details and special peculiarities of
the behavior under the different classes of stimuli will be described.

I. MECHANICAL STIMULI

When Paramecium strikes in its forward course against a solid ob-
ject, it responds usually by the avoiding reaction, as described in the
preceding chapter. In such cases the stimulus affects the anterior end
of the animal. But if mechanical stimuli affect other parts of the body,
will this alter the nature of the reaction? This question may be an-
swered by drawing a glass rod to an extremely fine point and touching
various parts of the body with this point under the microscope. The
first discovery that we make by this method of experimentation is that
the anterior end is much more sensitive than the remainder of the body
surface. If the anterior end is touched very lightly, the animal responds
by a strong avoiding reaction, while the same or a more powerful stimu-
lus on other parts of the body produces no reaction at all. There is
some evidence drawn from other sources’ that the region immediately
about the mouth is likewise very sensitive.

A second fact brought out by these experiments is that a stimulus
on the posterior part of the body produces a different reaction from a
stimulus in front. If we touch the anterior end, or any point on the
anterior portion of the body back nearly to the middle, the typical avoid-
ing reaction is produced. But if we touch the middle or the posterior
part of the body of a resting specimen, the animal, if it reacts at all,
merely moves forward.

1 See Chapter V.
59

60

BEHAVIOR OF THE LOWER ORGANISMS

On the other hand, as we have seen in the preceding chapter, the
direction in which the animal turns in the avoiding reaction does not
depend on the side of the body stimulated. The animal turns toward
the aboral side as well when that side is touched, as when the oral side
receives the stimulus.

The reactions which we have thus far described have the effect of
removing the animal from the object with which it comes in contact, so

Fic. 45.
— Parame-
cium at rest
against a
cotton fibre,
showing the
motionless
cilia in con-
tact with the
fibre.

that they may be called negative reactions. But under
certain conditions, not very precisely definable, Paramecium
does not avoid the object which it strikes against. On the
contrary it stops and remains in contact with the object.
This seems most likely to happen when the animal is swim-
ming slowly, so that it does not strike the object violently.
But this does not explain all cases; many individuals seem
much inclined to come to rest against solids, while others do
not. Often all the individuals in a culture are thus inclined
to come to rest, while in another culture all remain free
swimming, and give the avoiding reaction whenever they
come in contact with a solid. Observing a single swim-
ming specimen, it is often seen to react as follows. When
it first strikes against an object it responds with a weak
avoiding reaction, — swimming backward a short distance,
turning a little toward the aboral side, then swimming for-
ward again. Its path carries it against the object again,

whereupon it stops and comes to rest against the surface.
The objects against which Paramecium strikes under normal con-
ditions are usually pieces of decaying vegetable matter or bits of bacte-

rial zoédgloeea. Remaining in contact

with these helps it toobtain food. The
cilia that come in contact with the
solid cease moving, and become stiff
and set, seeming to hold the Parame-
cium against the object (Fig. 45).
Often it is only the cilia of the anterior
end that are thus in contact and im-
movable; in other cases cilia of the
general surface of the body show the
same condition. Meanwhile, the cilia
of the oral groove continue in active
motion, so that a rapid current passes
from the anterior end down the groove
to the mouth (Fig. 46). This cur-

Fic. 46. — Paramecium at rest with
anterior end against a mass of bacte-
rial zodgloea (a), showing the currents
produced by the cilia.

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 61

rent of course carries many of the bacteria found in the zodgloea or
on the decaying plant tissue; these serve as food for the animal. The
cilia of the remainder of the ,body usually strike only weakly and
ineffectively, so that the currents about the Paramecium are almost all
due to the movements of the oral cilia. The body cilia directly behind
those in contact with the solid are usually quite at rest.

The function of this positive contact reaction is evidently, under
ordinary conditions, to procure food for the animal. But Paramecium
shows no precise discrimination, and often reacts in this way to objects
that cannot furnish food. Thus, if we place a bit of torn filter paper
in the water containing the animals, we often find that they come to
rest upon this, gathering in a dense group on its surface, just as they do
with bits of bacterial zodgloea (Fig. 47). The oral cilia drive a strong
current of water to the mouth, as usual, but this bears no food. To
bits of thread, ravellings of cloth, pieces of sponge, or masses of pow-
dered carmine, Paramecium may react
in the same way. In general it shows a
tendency to come to rest against loose or ro.
fibrous material; in other words, it re-
acts thus to material with which it can
come in contact at two or more parts of
the body at once. To smooth, hard _ Fic. 47. — Paramecia gathered
materials, such as glass, it is much less reas RISES GOES STO Eee
likely to react in this manner, so that it
clearly shows a certain discrimination in this behavior. These hard
substances, it is evident, are less likely to furnish food than the soft
fibrous material to which Paramecium reacts readily. But under cer-
tain conditions Paramecium comes to rest even against a smooth glass
surface, or against the surface film of the water. Specimens are often
found at rest in this manner in the angle between the surface film of a
drop of water and the glass surface to which it is attached.

Paramecia often behave in the manner just described with reference
to bodies of very minute size,— to small bits of bacterial zoéglcea, or
to a single grain of carmine. Such objects are of course too small to
restrain the movements that naturally result from the activity of the oral
cilia in the contact reaction. These cilia continue to beat in the same
manner as when the object is a large one, producing currents similar to
those shown in Fig. 46. This ciliary motion of course tends to drive
the animal forward, and since all the active cilia are on the oral side, it
tends also to move the animal toward the aboral side. The resultant
of these two motions at right angles is movement in the circumference
of a circle. The animal moves in the lines of the water currents shown

62 BEHAVIOR OF THE LOWER ORGANISMS

in Fig. 46, but in the opposite direction; it is, as it were, whirled about
in its own whirlpool. The resulting path is shown in Fig. 48. This
circular movement, with the oral side
ys directed toward the centre of the
ss ee circle, is seen only in specimens show-
eo by r
‘ ye

ing the contact reaction to objects of

/ ‘Minute size.

f The contact reaction modifies
H strongly the reactions to most other
1 stimuli; this is a matter which will
\

be taken up later.

Thus when Paramecium comes
in contact with a solid object, it may
react in three different ways. First,
it may react either positively or
negatively, this depending partly on

Fic. 48.— Circular path followed by the intensity of the stimulus, partly
Sie cake reacting to contact witha 4 the physiological condition of the

Paramecium. If it reacts negatively,
this reaction may take either one of two forms. If the stimulation
occurs at the anterior end, the animal gives the avoiding reaction;
if it occurs elsewhere, the animal merely moves forward.

-
=

2. REACTIONS TO CHEMICAL STIMULI

The reactions to chemical stimuli occur through the avoiding reaction
described in the preceding chapter. As we have seen, the avoiding
reaction is produced as a rule by a change from one chemical to another.
With regard to this relation, there are certain facts of importance.

In all cases a certain amount of change is necessary to produce
reaction; that is, the chemical must be present in a certain concentra-
tion before reaction is produced. The sensitiveness of different indi-
viduals varies greatly, and even that of given individuals changes much
with changes in the conditions. It is therefore not possible to establish
for any given chemical the weakest concentration that causes the avoid-
ing reaction. But the animals when in ordinary water are very
sensitive to the common inorganic chemicals, reacting to very weak solu-
tions. Thus the weakest solutions causing reaction have been found to
be for various chemicals about as follows: —

Sodium chloride, 4; to 345 per cent (#45 to x} normal); potassium
bromate, about s4, per cent; sodium carbonate, about 345 to 345 per
cent; copper sulphate, about <4, per cent; potassium hydroxide, about

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 63

gto per cent; sodium hydroxide, g45 per cent; sulphuric acid, x45 per
cent of an ordinary laboratory solution; hydrochloric acid, ¢}5 per cent
of the usual solution; alcohol, 1 per cent; chloral hydrate, 2 per cent.
For the inorganic chemicals, many of these solutions are so weak as not
to affect at all the sense of taste in man.

Is the reaction of Paramecium to solutions due to the chemical
properties of the dissolved substance, or to its osmotic pressure? This
question may be answered from the data which we possess (partly
given above) as to the weakest solutions which cause reactions. If
the reactions are due to osmotic pressure, then solutions having equal
osmotic pressure must have equal stimulating power. The results of
the experiments on the weakest solutions necessary to cause reaction
show that this is not true. Thus, if the osmotic pressure of a solution
of sodium chloride that will barely cause the reaction is taken as unity,
the osmotic pressures of solutions of a number of other substances hav-
ing the same stimulating effect are as follows: potassium bromate, $;
sodium carbonate, s4;; copper sulphate, 3+; potassium hydroxide, +5;
sulphuric acid, 45; ethyl alcohol, 8. The stimulating effect is not then
proportional to the osmotic pressure, and must be due to the chemical
properties of the substances in solution.

This is further shown by the fact that Paramecia will enter solu-
tions of sugar and of glycerine having osmotic pressure many times as
great as that of a solution of sodium chloride which they avoid. They
swim into a 20 per cent solution of sugar or a 10 per cent solution of
glycerine without reaction. The solutions are so concentrated that
they cause plasmolysis; the Paramecia shrink into flattened plates. ”
Just as the shrinking becomes evident to the eye of the observer, the
Paramecia react in the usual way, by swimming backward and turn-
ing towards the aboral side. But this is as a rule too late to save them,
and they die in the dense solution. Thus it is evident that osmotic press-
ure, acting by itself, produces the same “avoiding reactions” as do
other stimuli, but the result is not produced till the Paramecia are
already injured beyond help. The reactions to most solutions are then
clearly due to their chemical properties.

Is the avoiding reaction that is produced by chemicals due directly
to the injuriousness of the substance? This question may be answered
by a series of experiments based on a method similar to that used in
determining whether the reaction is due to osmotic pressure. If the
reaction is due to the injuriousness of the chemicals, then two substances
which are equally injurious must have equal powers of inducing reac-
tion; in other words, the repelling powers of any two substances must
be proportional to their injurious effects.

64 BEHAVIOR OF THE LOWER ORGANISMS

An extensive series of experiments has shown that this is not true
(Jennings, 1899 c; Barratt, 1905). We may compare, for example, the
effects of chromic acid and of potassium bichromate. The weakest
solution of the former which kills the Paramecia in one minute is +5
per cent; the weakest solution of the latter having the same effect is
1 per cent. Hence the chromic acid is 150 times as injurious as the
potassium bichromate.

On the other hand, the weakest solution of chromic acid that sets
in operation the avoiding reaction is still =45 per cent, while potassium
bichromate has the same effect in a 345 per cent solution. The repel-
lent power is thus not proportional to the injurious effects; the potas-
sium bichromate is repellent in a strength 5/5 that which is immediately
injurious, which chromic acid does not repel until it has reached a
strength that is already destructive. Similar relations are found for
other pairs of substances. Thus the stimulating power of sodium
chloride is ten times that of cane sugar, in proportion to its injuriousness.

Comparing a large number of chemicals from this point of view,
it has been found that they may be divided into two classes. On the
one hand are a number of substances which must’be classified with
potassium bichromate and sodium chloride, because their stimulating
power is strong in proportion to their injurious effects. Paramecia
avoid these substances markedly; if a drop of a strong solution of one
of them is introduced into a preparation of the infusoria, it remains
empty, and none of the infusoria are killed by it. On the other hand,
there is a large number of substances which, like chromic acid and
sugar, produce stimulation only where they are strong enough to be
immediately injurious. When a strong solution of one of these is brought
into a preparation of Paramecia, it proves very destructive, for the ani-
mals as a rule do not react until they have been injured. The follow-
ing table (from Jennings, 1899 c) shows the distribution of various
chemicals from this point of view: —

TABLE

1. Repellent power strong in proportion| 2. Repellent power very weak in pro-
to injurious effects ; reaction protective. | portion to injurious effects; reaction not

LiCl, NaCl, KCI, CsCl, completely protective.

LiBr, NaBr, KBr, RuBr, HF, HCl, HBr, HI, H,SO, HNO,,
Lil, NaI, KI, Rul, Acetic acid, Tannic acid, Picric acid,
Li,CO,, Na,CO,, K,CO,, Chromic acid, Ammonia alum, Ammonio-
LiNO,, NaNO,, KNO,, ferric alum, Chrome alum, Potash alum,
NaOH, KOH, NaF, KF, CuSO, CuCl,, ZnCl,, HgCl,, AICI,, Cop-
NH,F, NH,Cl, NH,Br, NH,I, per acetate, Cane sugar, Lactose, Maltose,
CaCl,, SrCl,, BaCl Dextrose, Mannite, Glycerine, Urea.

Ca(NO,)o, St(NO,), Ba(NO,)o
Potassium bromate, Potassium perman-
nate, Potassium bichromate, Potassium

erricyanide, Ammonium bichromate.

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 65

This table shows that the relative repellent power of different sub-
stances bear a somewhat definite relation to their chemical composi-
tion. All alkalies and compounds of the alkali and the earth alkali
metals (save the alums, where the proportion of the metals is very small)
have a relatively strong repellent effect; most other compounds have not.

While our general result is that the stimulating powers of different
chemicals are not proportional to their injurious effects, yet one further
fact of importance comes out clearly. All substances, whatever their
nature, do produce, as soon as they become injurious, the avoiding
reaction. With all the substances in the second column the avoiding
reaction is produced when a strength sufficient to be injurious is reached
and the reaction seems clearly due to the injuries produced. The
significance of this fact will be discussed later.

In the chapter preceding the present one, we have seen that Para-
mecia collect in certain chemicals, owing to the fact that passage out
- of these causes the avoiding reaction. The two chief classes of chemi-
cals in which the animals collect are acids and oxygen.

Paramecia collect in all weakly acid solutions, no matter what acid
substance is present. Sulphuric, hydrochloric, nitric, hydriodic, and
many other inorganic acids; acetic, formic, carbonic, propionic, and
other organic acids, have been tested, and the animals have been found
to gather in all. The Paramecia collect even in solutions of poisonous
acid salts, such as corrosive sublimate and copper sulphate, where they
are quickly killed. In all these cases they swim into the solution with-
out reaction, but give the avoiding reaction at passing out. They
give the avoiding reaction also after the injurious chemical begins to
act on them, but under the circumstances this does not save them from
destruction.

It seems remarkable that the animals should thus tend to gather in
acids, when, as is well known, the decaying vegetable infusions in which
they live are usually alkaline in character.

Specimens in water that is decidedly alka- «SN no ae
line collect even more readily in acids than RS ihn iis
do those in a neutral fluid. ou < & att
A solution may contain both an acid lS
and a repellent substance, as when 3 per * eee ae

cent acetic acid is mixed with } per cent Fao, » apc Gellectinia of Pia
sodium chloride. In this case a curious mecia about the periphery of a
effect is produced. The Paramecia gather "™*t® of Salt and acid.
in a ring about the outer edge of the solution, as in Fig. 49. They are
repelled both by the inner fluid and the surrounding water. The path
of a Paramecium in such a ring is similar to that shown in Fig. 50.

F

66 BEHAVIOR OF THE LOWER ORGANISMS

Strong acid solutions cause the avoiding reaction as do other chemi-
cals. If a drop of strong acid solution is introduced into a preparation
of Paramecia, the animals collect about its periphery, where the acid
is diluted by the surrounding water, just as in Fig. 49. Individuals
which swim against the inner strong acid respond by giving the avoid-

ing reaction in a very pronounced way, — swim-
ming far backward and turning toward the aboral
side, for perhaps two or three or more complete
turns. They react also at the outer boundary of the
acid ring, so that within the ring the individual
Paramecium follows such a path as is shown in
Fig. 50.
Often the reaction is not produced at the inner
Aba te aes boundary of the ring, by the strong acid, until the
in such aringasisshown Paramecium has entered far enough to be injured,
ae PNG 40: or even killed. A drop of strong acid introduced
into a preparation is usually soon surrounded by a zone of dead
animals. Acids, as we have seen (p. 64), belong with those substances
which do not produce the avoiding reaction till they have become
directly injurious.

Paramecia do not, under usual conditions, collect in oxygen. If
we introduce an air bubble or a bubble of oxygen into a slide prepara-
tion of Paramecia, they do not as a rule collect about it. But if the
outer air is excluded from this preparation by covering its edges with
vaseline, and it is allowed to stand for a long time, the behavior changes.
The oxygen has of course become nearly exhausted and now the Para-
mecia gather about the air or the oxygen. The collections are formed
in exactly the same way as are those in acids.

Thus the experiments show that all reactions to chemicals take place
through the avoiding reaction, and this reaction is produced by a change
in the intensity of action of the chemical in question. With some chem-
icals, or under certain conditions, it is a change to a greater intensity
that produces the avoiding reaction; in other cases it is a change to a
less intensity that produces the reaction. With acids both an increase
and a decrease beyond a certain intensity produce reaction. We may
express the facts for all chemicals in the following general way. For
each chemical there is a certain optimum concentration in which the
Paramecia are not caused to react. Passage from this optimum to
regions of either greater or less concentration causes the avoiding reac-
tion, so that the animals tend to remain in the region of the optimum,
and if this region is small, to form here a dense collection. For, acids
and for oxygen the optimum is a certain very low concentration. For

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 67

most other chemicals the optimum is zero; an increase in intensity by
any effective quantity produces the avoiding reaction, while decrease in
intensity has no effect. Hence the Paramecia tend to collect where none
of the chemical is present.

The point needs to be brought out clearly that it is not merely pas-
sage from the absolute optimum that induces reaction, but passage in
a direction leading away from the opti-
mum. Toconstant conditions, even when
not optimal, Paramecium becomes ac-
climatized ; it may live for example in a
qo per cent salt solution, though pas- A
sage from water to this causes reaction.
While in this salt solution, passage into
conditions lying still farther from the
optimum, as into 4 per cent salt solu-
tion, causes the avoiding reaction, while
passage to conditions lying nearer the B
optimum produces no reaction. Ac-
climatization to non-optimal conditions
is an ever present factor in the behavior
of the organisms. ‘This is another way
of stating the fact that change is the
chief factor inducing reactions. c

Acids then take a peculiar position in
among chemicals merely in the fact that Renny
a certain positive concentration forms |,

5 IG. 51. — Collection of Paramecia
the optimum, passage to a lower CON- about a bubble of COg. a is a bubble of
centration inducing reaction. The pe- it 4 of COs. A shows the preparation

- z ‘ S two minutes after the introduction of the
culiar behavior of Paramecium with Co.; B, two minutes later; C, eighteen
respect to acids plays a large part in minutes later.
its life under natural conditions. Paramecia produce carbon dioxide
in their respiratory processes as do other organisms. This substance
when dissolved in water produces an acid solution, the acidity being
due to carbonic acid. In such a solution Paramecia gather as in
other acids. This may be shown by introducing, by means of a capil-
lary pipette attached to a rubber bag containing the gas, a small
bubble of carbon dioxide into a slide preparation of Paramecia. ‘The
infusoria quickly gather in a dense collection about the bubble, at first
pressing closely against it (Fig. 51, A). Later the Paramecia spread
out with the diffusion of the carbon dioxide (B). After a time the ani-
mals are usually found chiefly about the margin of the area containing
the carbon dioxide (C).

68 BEHAVIOR OF THE LOWER ORGANISMS

Now, the Paramecia gather in the solution of carbon dioxide pro-
duced by themselves, just as in that due to other causes. In this way
dense spontaneous groups are formed, in which the phenomena seen
in the collections about bubbles of carbon dioxide are reproduced. If
a large number of Paramecia are mounted in water on a slide, they do
not remain scattered, but soon gather in one or more regions (Fig. 52).
Within such groups the individuals move about in all directions. On
coming to an invisible outer boundary, they give the avoiding reaction
in a mild form, so that they do not leave the group. The area covered
by the group does not remain of the original size, but slowly enlarges,
as shown in Fig. 52. It continues thus to increase in size until it covers
the whole preparation. ,

By the use of proper indicators it can be shown that such spontane-
ous groups contain an acid, and this is beyond doubt due to the carbon
dioxide known to be produced in res-
piration. The groups are formed in
the following way. Two or three Para-
mecia by chance strike against some
small, loose object, a roughening of the
surface of the glass, or the like, and
come to rest, in the way described in
our account of the reaction to mechan-

oou a _.d| | ical stimuli. They of course produce
Be. ‘af < dl | carbon dioxide, which diffuses into the
eee ae ‘|| | surrounding water. Other Paramecia

that swim by chance across this area of
carbon dioxide of course stop and re-
main. ‘They too produce carbon diox-
ide, so that the area grows in size; more
Paramecia enter it, and finally a large
and dense collection is formed. The
area occupied by such a collection con-
tinually increases in size, because the

Fic. 52.—Spontaneousgroupsformed Paramecia continue to produce carbon
by Paramecia. A, B, C, successivestages ,. . 3 - x
in the spreading out of such groups. dioxide, and this continues to diffuse

through the water.

The tendency of Paramecia to gather in regions containing carbon —
dioxide plays a large part in their life under natural conditions, and
this, together with the fact that they themselves produce carbon dioxide,
explains many peculiar phenomena in their behavior. When placed in
tubes or vessels of any kind, Paramecia usually show a tendency to
collect into groups or clouds, having a definite boundary (Fig. 53).

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 69

This is of course a result of their reaction to carbon dioxide produced
by themselves. In all experimental work on the reactions of these
organisms to stimuli it is
necessary to take these wee,
facts into account. For eeee ada uertecna tyes
example, in order to get te
clear results in, such
work, Paramecia must not
be taken with a pipette
directly from a dense
collection in a culture
jar, and at once mounted | «.
on a slide. Such col- | *
lections contain carbon
dioxide, which may be-
come unequally distrib-
uted throughout the
preparation, as a result
of the fact that some of
the water outside the

1 to ]j Fic. 53. — Spontaneous collections of Paramecia, due to
collection is li kely 0 be COzg. A, Collections formed in an upright tube, after Jensen.
taken up with the Pl- B, Collection formed beneath a cover-glass, when water is
pette at the same time. t#ken directly from a dense culture of Paramecia. C, Collec-

tion in the bottom of a watch-glass.

The Paramecia quickly
gather in the region containing most carbon dioxide, and their reac-
tions to other substances are inconstant and irregular, owing to the
interference due to the reaction to carbon dioxide (Fig. 53, B). For

experimental work it is always necessary before each experiment to |
place a few drops of the .water containing the Paramecia in the bot-
tom of a shallow watch-glass, and to aérate it thoroughly by stirring it
and bringing it into contact with the air by means of the pipette.
Then this aérated water and its contained Paramecia must be used for
the experiments. This aération must be repeated before each experi-
ment, and the test for the reaction to other chemicals must be made
immediately after the Paramecia are mounted, before they have had
time to produce an appreciable quantity of carbon dioxide. If these
precautions are neglected, the reactions of the Paramecia are incon-
stant, and the results of experiments are likely to be very misleading.
Paramecia in a solution of carbon dioxide react to other agents in a
manner entirely different from the reaction of individuals in water not
containing carbon dioxide. The account of their reactions given in
the present chapter assumes that the carbon dioxide has been in every

go BEHAVIOR OF THE LOWER ORGANISMS

case removed from the water. The experimental results described
cannot be verified unless this is done.

In general it cannot be too much emphasized that in all experimental
studies on the behavior of Paramecium close attention to their reac-
tions with reference to carbon dioxide is necessary. When inconstant
results are obtained, or results seeming to contradict those noted by
other observers, it will often be found that inattention to the carbon
dioxide produced by the animals is at the bottom of the difficulty.

3- REACTIONS TO HEAT AND COLD

As we saw in the preceding chapter, a change to a temperature de-
cidedly above or decidedly below the optimum causes Paramecia to
give the avoiding reaction, while a change leading toward the optimum
does not. As a result the animals collect in temperatures as near the
optimum as possible.

The effects of heat and cold differ slightly, since heat increases the
rapidity of movement, while cold reduces activity. Both produce the
avoiding reaction in the same way, but in heated water the reaction is
continued violently till the animals escape or are killed, while in ice
water the animals after a time become benumbed and sink to the bottom.

The reactions to heat and cold are seen in a striking way when the
Paramecia are placed in a long tube or trough, one end of which is heated
while the other is maintained at the normal temperature, or is cooled.
The Paramecia then pass to the region that is nearest the optimum,
forming here a collection. By changing the temperature of the ends
or of the middle, the Paramecia may be driven from one end to the other
or caused to gather in any part of the trough. Such experiments were
devised by Mendelssohn (1895, 1902, 1902 a, 6). He passed tubes
beneath the middle and ends of the trough or slide bearing the animals,
and through these tubes he conducted water of different temperatures.
By changing the connections of the tubes, that end of the trough which
is at first heated may later be cooled, etc., without disturbing the ani-
mals in any other way.’

If in this way we heat the water at one end of the trough to 38 degrees
while we cool the opposite end to 10 degrees, the Paramecia collect in
an intermediate region. By varying the temperatures at the two ends,
the infusoria may be driven back and forth, as represented in Fig. 54,
taken from Mendelssohn. By grading the temperatures properly,
the sensitiveness of Paramecium to changes in temperature may be
measured, and the optimum temperature determined very accurately.

1A simple apparatus of this sort is described and figured in Jennings, 1904.

THE BEHAVIOR OF INFUSORIA,; PARAMECIUM 71

Mendelssohn found that the optimum temperature for Paramecium
lies, under ordinary conditions, between 24 and 28 degrees C.,
and that when there is a difference of but 3 degrees C. between the
two ends of a trough 1o centimeters in length, the Paramecia gather
at the end of thetrough :
nearest the optimum bat tie a9 Re
(see Fig. 54). If the
end a has a tempera-
ture of 26 degrees, the
end b 38 degrees, the
Paramecia gather at
the end a; if now the
temperature of the two
ends is interchanged,
the Paramecia travel
from a toward b, and
collect there. The
same results are pro-
duced if one end has
a temperature of 10 10°

degrees, the other of Fic. 54. — Reactions of Paramecia to heat and cold, after
Mendelssohn (1902). At a@ the infusoria are placed in a trough,

* 6 degrees, save that both ends of which have a temperature of 19 degrees. They are
in this case the Para- equally scattered. At b the temperature of one end is raised to
mecia gather at the 38 degrees while the other is only 26 degrees. The infusoria col-
* lect at the end having the lower temperature. At c one end has

end having the higher atemperature of 25 degrees, while the other is lowered to 10 degrees.
temperature. Tf Para- The animals now collect at the end having the higher tempera-

: ture.
mecia are kept for

some hours at a temperature of 36 to 38 degrees, the optimum be-
comes higher, — about 30 to 32 degrees; otherwise the phenomena
remain the same.

Observation of the movement of the individuals shows that the re-
actions in these experiments take place in the following manner. As one
end of the trough is heated above the optimum, the Paramecia in that
region are seen to become more active, darting about rapidly in all direc-
tions. Those that come against the sides or end of the vessel respond by
the avoiding reaction; they are thus directed elsewhere. Individuals
that are swimming toward the hotter region likewise give the avoiding
reaction, —at first in but a slightly marked form, stopping, swinging
the anterior end about in a circle, as illustrated in Figs. 37—39, and “try-
ing’ forward movement in a number of different directions. This con-
tinues as long as they are moving toward the warmer region; but as
soon as their direction of movement leads them toward the cooler region,

72 BEHAVIOR OF THE LOWER ORGANISMS

the avoiding reaction ceases, and they continue to swim in that direc-
tion. At that end of the trough which is cooled below the optimum,
similar effects are produced, save that the reaction is less rapid, and the
Paramecia therefore leave this region much more slowly than they do
the heated end.

Thus after a time the direction of movement of all the individuals in
the hot or cold end of the trough has become changed, and all are moving,
often in a well-defined group, toward the optimum region. Thus we
may observe in these temperature reactions a well-defined common
orientation of a large number of organisms; all are headed toward the
optimum. This orientation is brought about, as we have seen, by ex-
clusion. That is, movement in any other direction is stopped, through
the production of the avoiding reaction, so that all finally travel in this
one direction. Or, to put it more accurately, the Paramecia try every
possible direction, through the avoiding reaction (Figs. 37-39), till
finally they all find the only one which does not cause stimulation; in
‘this direction: they continue to move. The method of reaction, by
systematic trial of all directions, is such as to find any existing avenue
of escape, no matter how narrow it may be.

4. REACTION TO LIGHT

To ordinary visible light Paramecium is not known to react in any
way. If light is allowed to fall on the animals from one side only, or
if one portion of the vessel containing them is strongly lighted while the
rest is shaded, this has no observable effect on their movements or
distribution.

But Hertel (1904) has recently shown that to powerful ultra violet
light Paramecium does react. The ultra violet rays employed by Hertel
came from a magnesium spectrum; they were of a wave length of
280 py. When part of adrop of water containing Paramecia
was subjected to this light, the animals in the lighted region at once
began to move about rapidly. They therefore passed quickly into
the region not lighted. Specimens moving about in this shaded region
stopped at once on reaching the boundary of the lighted area, and turned
away. It is evident that the reaction to light is by the usual avoiding
reaction, though the details of the movement were not observed by
Hertel.

When the animals were unable to escape from the light, their move-
ment became uncoérdinated, and in ten to fifty seconds it ceased. The
animals were dead.

THE BEHAVIOR OF INFUSORIA,; PARAMECIUM 73

5. ORIENTING REACTIONS, TO WATER CURRENTS, TO GRAVITY, AND
TO CENTRIFUGAL FORCE

In the reactions which we have thus far considered, the infusoria do
not become oriented in any precise way with relation to the direction of
action of the stimulating agent. But to water currents, to gravity, and
to centrifugal force the animals at times react in such a way as to bring
about a definite orientation, with the body axis of all the reacting
individuals in line with the external force. In a water current the
anterior end is directed up stream; under the influence of gravity the
anterior end is directed upward, while when subjected to a centrifugal
force the anterior end is directed against the action of the force.

How are these results produced, and why do the organisms take a
definite axial orientation under the action of these stimuli, while they do
not under most other stimuli?

In the reactions to water currents and to gravity, direct observation
has shown that the orientation is produced through the movements
which we have called the avoiding reaction. Under the action of a
centrifugal force, observation of individuals is impossible, but beyond
doubt the reaction is the same as that due to gravity.

A. Reactions to Water Currents

The reactions to water currents can best. be studied in a tube like
that shown in Fig. 55. By covering the two open ends with rubber caps
filled with air, and
pressing on these, the
water containing the
animals in the tube Fic. 55. — Tube used in studying the, reactions to water cur-
canbedriventhrough ***
the narrow part of the tube with any desired velocity. With a certain
velocity of current most of the individuals, both those that are free
swimming and those that are resting against the glass, are seen to
place themselves in line with the current, with anterior end up stream.
Some of the individuals usually do not react. In those that do, the
reaction is brought as follows: As soon as the current begins to act,
producing a disturbance in the water, the animals give the avoiding
reaction in a not very pronounced form. That is, a given individual
swims more slowly or stops, and swerves more strongly toward the
aboral side, thus swinging the anterior end about in a circle, as in
Figs. 37 and 38, “trying” various directions. It then starts forward
again in one of these directions. This reaction may be repeated sev-
eral times, till the infusorian finally comes into a position with anterior

74 BEHAVIOR OF THE LOWER ORGANISMS

end directed up stream. The reaction then ceases, and the infusorian
remains in this position, either swimming forward against the current,
or at rest against the wall of the tube. Sometimes the reaction is a
little more precise, the animal turning directly toward the aboral side
till the anterior end is directed up stream. This is commonly the
case with the individuals that are at rest against a solid. The reaction
of the resting specimens is less easily observed, for the current easily
carries them away from their attachment, when of course they behave
like other free specimens.

What is the cause of the reaction to water currents? Under natural
conditions the cilia of Paramecium are beating backward, driving a cur-
rent of water backward over the surface, especially in the oral groove.
If an external current moves in the opposite direction, or in some oblique
direction, it will of course act in opposition to the cilia on that part of
the body which it strikes, tending to reverse or disarrange them, and to
reverse or change the direction of the usual currents. It appears not
surprising that such a disturbance acts as a stimulus, causing the usual
avoiding reaction until the disturbance is corrected. The correction can
occur only when the animal is headed up stream; the current is then
passing backward over the body in the usual direction. The reaction
is essentially a response to a mechanical disturbance, comparable to that
due to the touch of a solid body.

If this is the correct explanation, as seems probable, then there should
be no reaction when the animal is completely immersed in a homogene-
ous current, — one moving at the same velocity in all parts. For as
Lyon (1904) has pointed out, under these circumstances the animal is
merely transferred bodily in a certain direction, along with the medium
surrounding it, and at the same rate. Its relation to the enveloping fluid
is the same as in quiet water; there is nothing to cause a disturbance.
“Stimulation implies a change of relation between organism and en-
vironment. But if both in all their parts are moving at the same veloc-
ity, their relations do not change, and the conditions for stimulation are
wanting” (Lyon, 1904, p. 150).". The animal should then react only
when either it is in contact on one side with a solid, or when the current
is moving more rapidly on one side than on the other, producing a shear-
ing effect, with the necessarily accompanying disturbing action. Whether
this is true or not is very difficult to determine, but observation seems to
indicate that it is.

*This consideration, as well as the fact that individuals resting against a surface
react to the current, shows the incorrectness of the theory put forward by the present
author (1904 /), in which stimulation was supposed to be due to the variations in pressure
produced through the varied movements of the animal in its spiral course.

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 75

Certain authors (Dale, 1901, Statkewitsch, 1903 a@) have reported that
Paramecia sometimes swim with the current. But in these cases ir-
regular currents have been used, such as are produced by stirring the
water containing the animals. Using a tube, the present author has
found the results to be practically uniform, the animals swimming up
stream. If the reverse reaction actually occurs at times, it must be due
to some change of internal condition, such as results in swimming back-
ward under certain circumstances; the direction of the current over the
body would be the same in the two cases.

If the explanation of the reaction to water currents above given is
correct, this reaction is clearly analogous to the compensatory move-
ments of higher animals, as Lyon (1904) has brought out for other
organisms. It is a response to unusual relations with the environment,
and tends to restore the usual relations.

B. Reactions to Gravity

In the reaction to gravity the animals place themselves with anterior
end directed upward, and as a result swim to the top of the vessel con-
taining them, forming a collection there (Fig. 56). If the
tube is inverted after the collection is formed, so that the
infusoria are now at the bottom, they again direct the ante-
rior end upward, and swim to the top. These results follow
in the same way whether the upper end of the tube is open
or closed, and they take place equally well when the

— temperature is kept uniform
by immersing the tube in
running water.

To determine the way
in which the reaction oc-
curs, itis necessary to direct
the lenses of a microscope
of long focus upon a region
where the animals are tak-
ing up the position with long \Y
axis in the direction of pj 7j5°5.

= Ae gravity. This may best be lected at the =o
1G. 57. — Tube used in observing . . of a_ vertic
the way in which Paramecium reacts to accomplished by placing the tube, after Jen-

gravity. animals in a U-shaped tube, sen (1893).

at first with the free ends upward. After the animals have become
grouped at the two free ends, the tube is inverted (Fig. 57). The
Paramecia now move upward, reach the cross-piece of the U, and

wee

76 BEHAVIOR OF THE LOWER ORGANISMS

move across it to the opposite side. Reaching this, they at first con-
tinue the course by swimming obliquely downward, to the point x.
Here the reaction occurs; the animals turn around and swim upward
again. Studying the movements of the Paramecia at this point, one ob-
serves that the forward motion becomes slower, while the spiral course
becomes wider. The animals swerve more strongly than usual toward
the aboral side, so that the anterior end swings about in a circle, as in
Figs. 37 and 38. Thus the animals are giving the avoiding reaction,
“trying” successively many different positions. This is continued or
repeated till after a time they come into a position with anterior end
upward. The strong swerving then ceases; the animals swim upward
in the usual spiral course.

The position of individuals at rest against a solid is usually quite
independent of gravity. The body axis may be placed at any angle with
the pull of gravity, with either end higher. The contact reaction inter-
feres with the reaction to gravity, preventing it almost completely. Yet
there is a tendency, even when in contact with a solid, to take a position
with anterior end above. If Paramecia are placed in clean water in a
clean, upright glass tube, in the course of time many individuals come to
rest against the perpendicular walls. It will now be found, in some
cases, that a considerable portion of the animals, though by no means
all, are resting with the body axis nearly in line with gravity and with
anterior end upward. When a swimming individual places itself in con-
tact with the wall, it is often seen to make a sudden turn toward the
aboral side, just as it comes to rest, till the anterior end is upward; then
it remains in that position. The proportion thus oriented with reference
to gravity is in some cultures sufficiently great, amounting perhaps to
half the individuals, to show that the position is not accidental. In

_ other cultures there may be almost no indication of any influence of
gravity on the position of the attached specimens.

The precise nature of the determining factor in the reaction to gravity
is very obscure. Jensen (1893) held that the reaction is due to the dif-
ference in pressure between the upper and lower portions of the organism.
The cilia on the side where the pressure was greatest (the lower side)
were supposed to beat more rapidly, thus turning the animal directly
upward. But, as we have seen above, exact observation of the move-
ments of the individuals shows that the reaction does not take place in
this way. Moreover, the difference in pressure between the two sides
of the organism is in certain reacting infusoria only one millionth of the
total pressure, and this difference seems beyond question too slight to
act as an effective stimulus.

Davenport (1897, p. 122) held that the reaction to gravity is due to

THE BEHAVIOR OF INFUSORIA,; PARAMECIUM 77

the fact that the resistance in moving upward is greater than the resist-
ance in moving downward, owing to the fact that the animal is heavier
than water. To the changes in resistance as it swims up or down, the
animal reacts. This view was accepted and elaborated by the author
of the present work (Jennings, 1904 #). But to this can be made an
objection analogous to that which is fatal to the corresponding view for
the reaction to water currents. Under the uniform action of gravity,
as Radl (1903, p. 139) has pointed out, it is not apparent how any such
difference of resistance could be perceived by the organism. The ani-
mal would, with the same action of the cilia, and overcoming the same
resistance, move somewhat more rapidly downward than upward. But
it is very questionable if this slight comparative difference in rate could
be perceived by the organism, — though this is of course not impossible.
In any case, the fact that resting individuals may react to gravity
appears fatal to the view at present under consideration.

The view having the greatest probability is perhaps that suggested
by Lyon (1905). The animal contains substances of differing specific
gravity; this Lyon has demonstrated. The distribution of these sub-
stances must change with the various positions taken by the animal.
When the anterior end is directed downward the redistribution of inter-
nal substances thus induced acts as a stimulus, causing the usual re-
action. The animal “tries”? new positions till it reaches one with
anterior end upward; then the reaction ceases and the animal remains
in the position so reached.

Whatever the cause for the reaction to gravity, the stimulation it
induces is evidently very slight, and its effect is easily annulled by the
action of other agents. As we have seen, the contact reaction usually
prevents the reaction to gravity. The same is true of most other stimu-
lating agents. Almost any other stimulus that may be present produces
its usual effect without interference from gravity, so that the reaction to
gravity is seen clearly only in the absence of most other stimuli. Thus,
if the walls of the vessel containing the animals are not clean, or if the
water contains many solid particles in suspension, often no reaction to
gravity can be observed.

Furthermore, the reaction to gravity becomes reversed under cer-
tain conditions. Sometimes nearly all the individuals in a given cul-
ture swim downward instead of upward. This result may be produced
in cultures having originally the more usual upward tendency, in a
number of different ways (Sosnowski, 1899; Moore, 1903). These
will be mentioned in our section on reactions to two or more stimuli.

78 BEHAVIOR OF THE LOWER ORGANISMS

C. Reaction to Centrifugal Force

Conditions similar to those due to gravity may be produced by a
centrifugal force, and Paramecia then react, as might be expected, in
the same way as to gravity. Jensen (1893) shows that if a tube contain-
ing Paramecia is placed in a horizontal position on a centrifuge and
whirled at a certain rate, the infusoria tend to swim toward that
end of the tube next to the centre. In a tube 12 cm. long, with the
inner end 2 cm. from the centre, the phenomena were well shown
when the tube was whirled at the rate of four turns per second, for ten or
fifteen minutes. In such a tube the Paramecia at the outer end, where
the movement is fastest, are carried by the centrifugal force, against
their active efforts, to the outer end of the tube; this is of course a purely
passive phenomenon. The remainder of the Paramecia swim toward
the end of the tube next the centre and collect there; this is the active
part of the reaction.

This movement toward the inner end of the tube is doubtless due to
the same causes, whatever they may be, that produce the upward move-
ment in the reaction to gravity. Lyon (1905) has shown that the body
contains substances of varying specific gravity, some of which collect,
under strong centrifugation, at that end of the animal which is at the
outer end of the tube. This redistribution is probably the cause of the
reaction to centrifugal force. If the passage of such substances into
the anterior end should act as a stimulus to the usual reaction, this
would produce the results actually observed.

6. RELATION OF THE ORIENTATION REACTIONS TO OTHER REACTIONS

We are now in a position to define the difference between these orien-
tation reactions and the others that we have described, and to see why
the result of the avoiding reaction is to produce a certain position of
the body axis in one set of cases, while it does not in the others.

In the reactions to mechanical stimuli, chemicals, osmotic pressure,
heat and cold, and powerful light, the avoiding reaction is caused by the
transition from one external condition to another; by a change in the
intensity of action of some agent,— the change being of such a charac-
ter as to lead away from the optimum. As a result, the organism tries
repeated different directions of movement (in the avoiding reaction) till
it hits upon one in which the transition is toward the optimum instead
of away from it; in this direction it continues. This does not require
the body axis to take any definite orientation, since as a rule there are
various directions in which the animal can move and be on the whole
approaching the optimum. Furthermore, the body axis might be in any
position, provided the movement were on the whole toward the optimum.

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 79

But in the reactions to water currents, gravity and centrifugal force,
it is a certain position of the body that results in stimulation; displace-
ment of the cilia, or of certain internal constituents, occur in certain
positions of the body, causing disturbances to which the animal reacts,
as usual, by the avoiding reaction. This reaction consists in successively
“trying,” not only different directions of locomotion, but also different
positions of the body axis, as a glance at Figs. 37-39 willshow. As soon
therefore as a position is reached in which the disturbance causing the
reaction no longer exists, the reaction of course stops; the animal there-
fore retains this axial position.’

A comparison of the reactions to these two sets of agents brings out
strongly the general adaptiveness and effectiveness of the reaction
method of the infusorian. The avoiding reaction is of such a charac-
ter as to bring about in a systematic way (1) different directions of
movement; (2) different axial positions; (3) different environmental
conditions (of temperature, chemicals, etc.). If any one of these puts
an end to the disturbance which caused stimulation, the reaction of
course stops at that point, and the animal retains the direction of move-
ment, axial orientation, or environmental condition thus reached. Ifa
certain axial orientation must be reached before the stimulating dis-
turbance ceases, then the result of the reaction will be to produce this
orientation. If the disturbance ceases before a common orientation of
all the individuals is reached, then no common orientation will occur.
In other words, the method of reaction is such as to bring about any
condition whatsoever that is required in order to put an end to stimula-
tion, — provided of course that this condition is attainable. It will
therefore produce in some cases a certain direction of movement, in other
cases a certain axial orientation, in other cases the retention of a certain
environmental condition, just as circumstances may require.

LITERATURE IV

A. Reactions to contact with solids: PUTTER, 1900; JENNINGS, 1897, 1899.

B. Reactions to chemicals: JENNINGS, 1897, 1899 ¢; GREELEY, 1904; BARRATT,
1905.
C. Reactions to heat and cold: JENNINGS, 1904; MENDELSSOHN, 1895, 1902,
1902 a, 1902 4.

D. Reactions to light: HERTEL, 1904.

£. Reactions to water currents: JENNINGS, 1904 4: LYON, 1904, 1905.

F. Reactions to gravity and centrifugal force: LYON, 1905 ; JENSEN, 1893; JEN-
NINGS, 1904 4; SOSNOWSKI, 1899; MOORE, 1903.

1 It is worthy of note that the position of orientation is not one in which a median
plane of symmetry takes up a definite position with reference to the external agent, as is
sometimes set forth. The infusorian when oriented continues to revolve on its long axis,
so that no more can be maintained than that the longitudinal axis (in reality the axis of
the spiral path) is in line with the orienting force.

CHAPTER V
BEHAVIOR OF PARAMECIUM (Continued )

REACTIONS TO ELECTRICITY AND SPECIAL REACTIONS

I. REACTIONS TO ELECTRICITY

THE reactions of Paramecia to electricity are more complex than
those to other stimuli. This is owing to certain factors peculiar to the
action of the electric current, which interfere with the usual reaction
method.

The gross features in the behavior under the action of electricity may
be seen as follows. The Paramecia are placed in a watch-glass or other
small vessel, and through the water containing them an electric current
is passed (Fig. 58, A). Unpolarizable electrodes should be used, though
the. gross features in the reaction
may be observed with platinum
electrodes. A current such as is
produced by six or eight chromic
acid cells is needed. As soon as the
current begins to pass, all the Para-
mecia swims toward the cathode or

Fic. 58. — A, General appearance of’ Paramecia reacting to the electric current. After
Verworn ( 1899). The current is passed by means of unpolarizable brush electrodes through
a cell with porous walls. The infusoria have gathered at the cathodic side. B, Magnified
view of a portion of the swarm as it moves toward the cathode: After Verworn.

negative electrode. The swarm of infusoria all moving in the same

direction present a most striking appearance (Fig. 58, B). If while

all are swimming toward the cathode the direction of the current is

reversed, the Paramecia at once turn around and swim toward the
80

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 81

new cathode. If the electrodes are small points, the Paramecia swim
in curves, such as are known to be formed by the current (Fig. 59).
If while all are moving
toward the cathode the cur-
rent is interrupted, the group
breaks up and the Paramecia
scatter in all directions.

If the current is at. first
very weak, the Paramecia do
not react sharply, only a few

Fic. 59. — A, Curves followed by Paramecia when
. ; pointed electrodes are used. B, Collection of Para-
of them swimming toward mecia behind the cathode, when the electrodes are

me cathode When, the placed close together. After Verworn (1899).

strength of the current is increased, more of the animals react and the
movement is more rapid, till at a certain strength of current practically
all are swimming rapidly to the cathode. With a further increase in
the current, the rate of progression toward the cathode becomes slower.
As the increase continues, the rate of swimming decreases till progress
nearly or quite ceases. The animals now remain in position, with
anterior ends directed toward the cathode, but not moving in either
direction. Increasing the current still farther, the animals begin to
swim backward toward the anode. At this time each Paramecium
is seen to have become deformed, being short and thick. If the cur-
rent is farther increased, the animals burst at one end and go to pieces.
These remarkable phenomena were first observed by Verworn (1889 a).

How is this striking behavior brought about? Why do the Para-
mecia first all go to the cathode, then in a stronger current stop, then
swim backward to the anode?

A. Reaction to Induction Shocks

In attempting to answer these questions, it will be best to take up
first the reactions to single induction shocks. To observe the reactions
accurately, the Paramecia must be placed in some viscid but not inju-
rious substance, such as the jelly produced by allowing a few quince
seeds to soak in a watch-glass of water. containing the animals (Statke-
witsch, 1904 a). This makes the movements so slow that they can be
followed under the microscope. The reaction to induction shocks under
these conditions has been studied especially by Statkewitsch (1903).
When an induction shock is passed through a drop of such fluid con-
taining Paramecia, the animals are found to react especially at that
part of the body which is next the anode. Here the cilia are suddenly

reversed, striking forward instead of backward; the ectosare contracts
G

82 BEHAVIOR OF THE LOWER ORGANISMS

sharply, and trichocysts are thrown out (Fig. 60). If the current is a
very weak one, only the reversal of cilia occurs; with a stronger current
the other phenomena

Ww’ appear. With a very
powerful _—current,

contraction and dis-
charge of trichocysts
occur also at the
4+ S> , wks i cathode, and with a
Zz further increase of
current, over the
whole body. . The
animal at the same
time becomes de-
formed and usually

f ‘ ar goes to pieces.
Fic. 60. — Effect of induction shocks on Paramecia in different oe f
positions. After Statkewitsch (1903). Trichocysts discharged, n the current o
cilia reversed, and contraction of the ectosarc, at the anodic side moderate strength

or end, in a moderate current. ped

the reversal of cilia,
beginning at the anode, quickly spreads over the entire body, causing
the animal to swim backward. This movement is the beginning of
the avoiding reaction. After swimming backward a short distance the
animal turns toward the aboral side and swims forward in a new
direction. Thus the reaction to an induction shock is of essentially the
same character as the reaction to other strong stimuli.

Paramecium reacts to induction shocks more readily, as might be
expected, when the sensitive anterior end is directed toward the anode.
When in this position, it reacts to currents that are too weak to produce
reaction in specimens occupying other positions. According to Roesle
(1902), Paramecium reacts more readily when the oral surface is toward
the anode than when in other positions, indicating that the region about
the mouth is especially sensitive. While this seems probable on general
principles, it was not confirmed by the thorough work of Statkewitsch
(1903). In some cases an induction shock, like a weak mechanical
stimulus, causes in place of the avoiding reaction a movement forward
(Roesle, 1902).

Since the animal is most stimulated when the anterior end is directed
toward the anode, and this stimulation causes as a rule the avoiding re-
action, one would expect that if the stimulation came repeatedly from
_ the same direction, the animal would after a time reach a position with
anterior end directed away from the anode. This is exactly what occurs.
If frequent induction shocks are passed in a certain direction through

\

\

N

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 83

the water, the animals all become pointed toward the cathode and swim
in that direction (Birukoff, 1899, Statkewitsch, 1903). This happens
even when the current is so weak that a single induction shock causes
no reaction. There is a summation of the effects of the successive
shocks until a reaction is produced (Statkewitsch, 1903). As most com-
monly used, induction currents pass alternately in opposite directions.
The induced current in one direction is due to the closing of the circuit
in the primary coil, while the immediately following current induced in
the opposite direction is due to the breaking of the circuit in the primary
coil. The induced currents due to the breaking of the circuit are, as is
well known, more powerful than those produced by the closing of the
circuit. When both currents pass through the preparation alternately,
Paramecia react primarily to the stronger ‘“‘break”’ currents. They
move toward the cathode of these stronger currents and are apparently
not affected by the weaker ‘“‘make” shocks (Birukoff, 1899, Statke-
witsch, 1903 a).

B. Reaction to the Constant Current

If in place of induction shocks a continuous electric current is used,
the result is the same as was described in the last paragraph. The
Paramecia place themselves with anterior end directed toward the
cathode and swim in that direction (Fig. 58).

From what we know of the behavior of Paramecium under the action
of other stimuli, we might suppose that the whole secret of this behavior
lies in the production of the avoiding reaction when the anterior end is
directed toward the anode. This reaction, continuing until a position
was reached where the anterior end was no longer stimulated, would
cause it to become directed toward the cathode. If the anode stimula-
tion still continued, now at the posterior end, the animal would continue to
swim forward toward the cathode, for to stimulation at the posterior end,
as we have seen, the animal responds by swimming forward. If this were
the method of reaction, the behavior under the electric current would
be of the same character as under the stimuli which the animal meets
in its natural existence.

But a study of the exact movements of the animals shows that there
is present another factor which is peculiar to the action of the electric
current. To detect this the precise movements of the cilia under the
action of the current must be examined. The cilia themselves may be
directly observed in specimens placed in some viscous medium (see
Statkewitsch, 1904 a). Or the effective movements of the cilia may be
determined by mingling with the fluid containing them a quantity of
finely ground India ink. By its aid the direction of the currents pro-

~84 BEHAVIOR’ OF THE LOWER ORGANISMS

duced by the cilia becomes evident.' In this way we find that it is not
alone at the anode that the electric current is active, but that a peculiar
effect is produced also at the cathode. Here the direction of the cilia
is reversed (Fig. 61) so that they point forward, and their effective stroke
is forward, tending to drive the animal backward. When the electric

ward in the usual way.
If the current is made stronger, this

current is weak and the animals are swim-

ming toward the cathode, the cilia are re-
versed only at the anterior end (Fig. 61, 1),
the reversal extending a little farther down
on the oral side than elsewhere. At the
anterior tip the water currents are forward
instead of backward (Fig. 62, a), and the
cilia themselves are clearly seen to be
pointed forward (Fig. 61, 1). | When the
animal is swimming most rapidly toward the
cathode, this effect is very slight; almost
Fic. 61. — Progressive cathodic
reversal of the cilia and change of
form in Paramecium as the con-
stant electric current is made
stronger. Thecathode is supposed
to lie at the upper end. The cur-
rent is weakest at 1, where only a
few cilia are reversed. 2-6, Suc-
cessive changes as the current is
gradually increased. After Statke-

cathodic effect increases. The cilia become
reversed farther and farther back, till with a
certain strength of the electric current the
cilia on the anterior half of the body are
striking forward, those on the posterior half
backward (Fig. 61, 3).” The water cur-
rents produced are in opposite directions,
making the animal the centre of a sort of

all the cilia of the body are beating back-
witsch (1903 a).

cyclonic disturbance in the water, which
gives a most extraordinary appearance (Fig. 62, 6). The two sets of
cilia oppose each other, so that the animal seems to be trying to swim
in two opposite directions at once. Up to a certain strength of the elec-
tric current the posterior cilia prevail over the anterior ones, so that the
animal swims forward. But the movement becomes slower and more
labored as the electric current is increased, until in time the two sets of
cilia balance each other. Then the animal remains in place, revolving
-rapidly on its long axis, or it shoots first a short distance forward, then
a little backward. With a still further increase of the electric current,
the cathodic effect increases to such an extent that the reversed cilia gain

1 The Paramecia must be in a thin layer of fluid; this may be attained by supporting
.the cover-glass on thin sheets of filter paper and introducing the current through this
paper.
? This peculiar effect was first observed by Ludloff (1895).

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 85

the upper hand, and the animal swims backward toward the anode.
The cilia are now reversed even behind the middle (Fig. 61, 4, 5). The
body is deformed, becoming short and thick, and pinched to a point at
the anode end, while the cathode end is swollen. Finally the animal
usually bursts and goes to

pieces ; before this happens \Y

almost all the cilia have Leite oe i

become reversed (Fig. Wn.

61, 6). 4 =e
When a Paramecium ORO apni <i

: ; or ‘

is transverse or oblique to \\

the direction of a current
at the time the circuit is
closed (Fig. 63, ¢, e), cer-
tain striking effects are
produced. If a current of
medium strength is em-
ployed, such as causes re-
versal of about half the
cilia, the following results
are observed. On _ the
anode side the cilia strike
backward, as usual. On
the cathode side the cilia
strike forward. As a re-

sult the animal, when in a
transverse position, must Fic. 62. — Water currents produced by the cilia in the

» electric current. @, Electric currents weak; water currents
turn directly toward the reversed only at cathodic tip. 06, Electric currents stronger;
cathode side, the cilia of Water currents reversed over cathodic half as far back as

both sides of the body the middle.

tending to produce this effect, as indicated by the arrows in Fig. 63,
cand e. This happens even when the oral side is directed toward the
cathode (Fig. 63, e). The animal then turns toward the oral side, —
a result never produced by other stimuli, and due to the peculiar
cathodic effect of the current.

This tendency to turn directly toward the cathodic side is compli-
cated in certain positions of the animal by the usual strong tendency to
turn, under the influence of stimuli, toward the aboral side, — that is,
to respond by the typical avoiding reaction. If the anterior end is
directed toward the anode at the time the circuit is closed, the animal in-
variably turns toward its aboral side, the cilia taking the position shown
in Fig. 63, 6. This method of turning is apparently due to the fact that

86 BEHAVIOR OF THE LOWER ORGANISMS

the backward stroke of the oral cilia is more powerful than that of the
opposing aboral cilia. For the same reason the animal turns toward
the aboral side even when in the position shown in Fig. 63, a, where it
would be more direct to turn toward the oral side. Between this posi-
tion (a) and the transverse position with oral side to the cathode (e),
there is a position in which the tendencies to turn in opposite directions
are exactly balanced (f). The animal tries, as it were, to turn in opposite
directions at the same time, so that it remains in position, though the

cS)
3

_

Cc

Fic. 63. — Effects of the electric current on the cilia of Paramecia, and direction of turning
in different positions. The oral side is marked by an oblique line. The large arrows show
the direction toward which the animal turns. The small internal arrows indicate the direction
in which the cilia of the corresponding quarter of the body tend to turn the animal. In all
positions save ¢ and e the cilia of different regions oppose each other. From a to d the turning
is toward the aboral side; from d to /, toward the oral side. At / the impulse to turn is equal in
both directions, and there is no result till by revolution on the long axis the animal comes into
a position with aboral side to the cathode.

cilia are beating violently, causing complicated currents in the water.
This independent and opposing activity of the cilia of different parts of
the body is characteristic of the effects of the electric current, and is not
found in the reactions to other stimuli. In the position shown in Fig.
63, j, the revolution on the long axis, which is a part of the normal
motion of the animal, soon interchanges the position of oral and aboral
sides, whereupon the infusorian of course turns at once towards the
aboral side, till its anterior end is directed toward the cathode.

Thus in a considerable preponderance of all possible cases the ani-

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 87

mal turns toward the aboral side, as it does under other stimuli. But
in certain positions (from d to /, Fig. 63) it turns directly toward the oral
side, a result not producible by other stimuli.

If the direction of the electric current is frequently reversed, certain
peculiar effects are produced. If the reversal occurs at the moment
when the anterior end has become directed toward the cathode, then the
animal continues to turn toward the aboral side till the anterior end is
pointed toward the new cathode. By repeated properly timed rever-
sals, the animals can be caused to spin round and round, — always
toward the aboral side.’ If the intervals between the reversals of the
current are made less, so that the animal has not yet become pointed
toward the cathode, it swings back over the space through which it has
turned. Thus. the animals may be made to swing back and forth or turn
round and round, remaining in the same spot, like animated galva-
nometers, — the anterior end pointing out the direction of the current.

If the rate of reversal is much increased,” so that the animals have
scarcely time to begin swinging in a certain direction before a new re-
versal occurs, then certain other phenomena result; these have been
described by Statkewitsch (1903, 1903 @). The Paramecia which are
swimming toward one electrode when the current is closed usually con-
tinue to swim in the same direction for a time, as if reacting to only one
of the current directions. Those not already pointed toward one of the
electrodes usually take quickly the transverse position. Thus, soon after
the beginning of the experiment, part of the animals are swimming
toward the electrode at the right, part toward that at the left, while the
rest are transverse. Soon those not transverse have reached the region
of the electrode toward which they are swimming. Thus the Paramecia
are now divided into three groups, —a group at the right swimming
toward the right electrode, another at the left swimming towards the
left electrode, and a central group swimming athwart the current (Fig.
64). After a time the transverse position is assumed also by those
directed toward the electrodes, especially if the current is made stronger
or the rate of reversal is increased. Thus at a later stage all or nearly
all are transverse; they swim across the current, some toward one side
of the preparation, some toward the other.

The reason for taking the transverse position when the current is
rapidly reversed seems to be as follows: We have seen above that to

1 As soon as a specimen has made a half revolution on its long axis, as may happen, it
of course seems to spin in the opposite direction, because the aboral side has taken up a
new position.

2 The strength of the current remaining the same in both directions, not varying as in
ordinary induction shocks.

88 BEHAVIOR OF THE LOWER ORGANISMS

single electric shocks the animals react more strongly when the anterior
end is directed toward the anode. Often there is no reaction when they
are in the opposite position. Consider a specimen that is oblique, as in
Fig. 63, b'. The current comes alternately from the right and left. To
the current coming from the left
(anode at the left) the Paramecium
reacts strongly, since its anterior end
is directed toward the anode. It
therefore turns its anterior end in the
opposite direction, —to the right.
To the opposite current, on the other
hand, it reacts little or not at all,
since the anterior end is not directed
toward the anode. Continuing thus
to react to the repeated currents from
the left, it must come into the trans-
verse position. Here the anterior end
has the same relation to both currents;
hence it swings as far to one side as to
the other. Since it changes its posi-
tion very little at any one reversal, it
maintains on the whole the transverse

Fic. 64. — Positions taken by Para- Pomc A
mecia in rapidly reversed currents. a, Posi- Under -a constant current in one
tions in weak currents, or in moderate direction, the general effect of the
currents at the beginning of the experiment. ? :
¢ and d, Positions taken in stronger cur- behavior is of course to cause the ani-
rents, or after the experiment has lasted for mals to pass to the cathode. Here they
some time. After Statkewitsch (1903 a). ‘ ;

may gather in a dense mass. But if
the cathode is so placed that the Paramecia can pass behind it, they do
this, thus reaching a region where the current is not acting (Fig. 59,
B). Here they swim about in all directions. If one comes by chance
again into the field of the current, it is at once returned, by the usual
reaction, to the region behind the cathode. If in any other way certain
areas are left free from the action of the current or with very little cur-
rent, the animals gather in these free areas. Birukoff (1899) has de-
scribed and figured many such cases, produced under induction shocks
by the aid of electrodes of different forms; his results have been extended
by Statkewitsch (1903 a).

It is evident that the reaction to the electric current differs funda-
mentally from the known behavior under other classes of stimuli. Under
other stimuli the movements are coérdinated, all tending toward the same
end, while in the electric current different parts of the body oppose each

c<; —S = —

——)
—

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 89

other. The behavior thus becomes uncoérdinated, lacking unity. The
animal seems to strive to perform two opposite actions at once. The
anterior cilia drive the animal backward, the posterior cilia forward. In
certain positions (Fig. 63, /) part of the cilia tend to turn the animal to
the right, others to the left. The action of the current is more local and
direct than that of other stimuli, producing opposed reactions in dif-
ferent parts of the body. The whole secret of this extraordinary be-
havior lies in the cathodic reversal of the cilia. If this cathodic effect
were non-existent, the behavior under the action of the electric current
would probably be the same as under other stimuli. The reaction due
to the anodic stimulation is, as we have seen, the same as that due to
other strong stimuli, and in the constant current the anodic cilia strike
backward in the usual way. If the anodic stimulation alone existed,
- the animal would doubtless become directed to the cathode by the method
of trial and would swim in that direction. But as the behavior actually
occurs, there is nothing like a trial of different positions. The cathodic
reversal of the cilia forces the animal directly into a certain orientation.
The reaction is not due, like that to chemicals, to the change in condi-
tions as the animal passes from one region to another. It is not due to
a tendency to collect about the cathode, for, as we have seen, if it is
possible, the animals go beyond the cathode. Moreover, in a strong
current there is no movement to the cathode, and in a still stronger
current the movement is away from the cathode, though the orientation
remains the same in both cases. All these peculiarities in the behavior
are due to the cathodic reversal of the cilia.

What is the cause of this fundamental feature of the reaction to the
electric current, — the cathodic reversal? Many theories have been
proposed to account for the reaction to electricity, though often these
do not touch this fundamental feature in any way. It will be better to
reserve an account of these theories until we have examined the behavior
of other infusoria under the action of electricity (see Chapter IX).

2. OTHER METHODS OF REACTION IN PARAMECIUM

In Paramecium there are certain methods of reacting to stimuli which
we have not yet described. These are, first, local contractions of the
ectosarc, and second, discharge of trichocysts. Neither of these seem to
play any important part in regulating the relation of the organism to
the surrounding conditions.

Slight local contractions of the ectosarc occur in response to many
stimuli. Since the ectosarc of Paramecium is not known to contain con-
tractile elements, the way in which these are brought about is unknown.

go BEHAVIOR OF THE LOWER ORGANISMS

A discharge of trichocysts is produced by many different agents.
The trichocysts are rodlike sacs in the ectosarc, perpendicular to the
outer surface. Their contents are ejected, under certain conditions, into
the water, forming long threads. According to some authors, these
threads have a definite structure, and are probably preformed within
the animal. Others suppose the threads to be formed by the coagula-
tion of a fluid contained within the sacs. After discharge of the tricho-
cysts the animal appears to be surrounded by a zone of radiating fibres
(Fig. 65).

The discharge of trichocysts under the influence of stimuli has been
studied especially by Massart (1901 a), and by Statkewitsch (1903).
Crushing the animal causes
discharge of trichocysts in
the region injured. Weaker
mechanical stimuli do not
have this effect. If the ani-
mal is heated rapidly till it
is killed, it discharges the
trichocysts before dying; if

Fic. 65. — Paramecium with trichocysts discharged, heated slowly, this effect is
as a result of the application of picric acid. not produced. Neither cold
nor increased osmotic pressure have any effect on the trichocysts. Many
chemicals produce the discharge, particularly various acids. Saturated
solution of picric acid causes a sudden discharge of all the trichocysts at
once. One-fourth per cent methylene blue produces a slow and irregular
discharge successively from different parts of the body.’ If any agent
acts on a limited portion of the body surface, the trichocysts of only that
region are discharged. Many chemicals kill the animal without dis-
charge of the trichocysts.

A weak induction shock causes discharge of the trichocysts at the
anode only (Fig. 60); a stronger shock causes discharge at both anode
and cathode. A still stronger shock causes discharge of the trichocysts
over the entire surface of the body (Statkewitsch, 1903).

In the discharge of the trichocysts we have a phenomenon compara-
ble to the definite reflex actions observed in various organs of higher
animals. The function of the trichocysts is uncertain. They are usu-
ally supposed to be weapons of defence. If the Paramecium is seized
by an animal which is attempting to prey upon it, the trichocysts will of
course be discharged from the injured region. But whether they really

1To demonstrate the discharge of the trichocysts it is convenient to use picric acid
alone or picric acid to which a little aniline blue has been added. In the latter case the
trichocysts become colored blue (Massart).

THE BEHAVIOR OF INFUSORIA; PARAMECIUM gI

serve for defence seems questionable. Certainly the infusorian Didi-
nium (Fig. 113), which is the chief enemy of Paramecium, is not hindered
in the least from seizing and devouring the animal by the discharge of
trichocysts. It is possible that the discharge is really an expression of
injury, —a purely secondary, even pathological, phenomenon, like the
formation of vesicles on the surface of an injured specimen.

LITERATURE V .

A. Reaction of Paramecium to electricity : VERWORN, 1889 a; LUDLOFF, 1895 ;
BIRUKOFF, 1899, 1904; ROESLE, 1902; PUTTER, 1900; STATKEWITSCH, 1903,
1903 @, 1904; JENNINGS, 1904 4; BANCROFT, 1905; COEHN AND BARRATT, 1905.

&. Discharge of trichocysts as a reaction: MASSART, I9oI a.

CHAPTER VI
BEHAVIOR OF PARAMECIUM (Continued)

BEHAVIOR UNDER Two oR More STIMULI; VARIABILITY OF BE-
- HAVIOR; FiIssION AND ConjuGATION; Dairy LIFE; GENERAL
FEATURES OF THE BEHAVIOR

I. BEHAVIOR UNDER TWO OR MORE STIMULI

THE behavior thus far described is that which takes place under the
influence of but a single kind of stimulation. But normally the condi-
tions are as a rule more complex than this; the animal is affected by
several sets of stimuli at once. What is the behavior under such condi-
tions? If, while the Paramecium is reacting to the stimulus a, the stim-
ulus 6 acts upon it, will it react in the usual way to 6? Or will it con-
tinue to react to a? Or will its action form a compromise between the
usual reactions to the two agents? Or will it, finally, react in a new
way, different from the usual reactions to either a or 0?

Let us examine first the behavior under the simultaneous action of
the contact stimulus and of other usual stimuli. As we have seen, the
contact stimulus often causes the animal to come to rest and behave in
a characteristic manner, while other classes of stimuli usually induce
the avoiding reaction or a movement forward. Thus opposite reactions
are induced by the two kinds of stimuli acting separately. What will be
the result when the two act together?

If the animal is at rest against a mass of vegetable matter or a bit of
paper under the action of the contact stimulus, and it is then struck
with the tip of a glass rod, we find that at first it may not react to the
latter stimulus at all. A touch that would cause a free swimming speci-
men to give the avoiding reaction in a pronounced way often has no evi-
dent effect on the quiet specimen. Sometimes, however, a touch coming
from behind causes the animal to move forward, still remaining in con-
tact with the solid object; it thus creeps a short distance over the sur-
- face of the solid. Finally, a strong blow on the anterior end causes the
animal to leave the solid and give the typical avoiding reaction.

Thus we find that under the simultaneous action of the two stimuli

92

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 93

the infusorian may either react to the more effective of the two, which-
ever it is, without regard to the other, or its behavior may be a sort of
compromise between the usual results of both.

If specimens showing the contact reaction are heated, it is found that
they do not react to the heat until a higher temperature has been reached
than that necessary. to cause a definite reaction in free swimming speci-
mens. Thus Piitter (1900) found that at 30 degrees C. all the
free specimens are strongly affected, moving about rapidly in all direc-
tions, while the attached specimens remain quiet or make only slight
vibratory movements. Many of them remain attached until the tem-
perature has reached 37 degrees, when the free specimens are dashing
about wildly. At this temperature or a-somewhat lower one the at-
tached. specimens become free; they then dash about as furiously as the
others. Thus the contact reaction interferes with the reaction to heat,
preventing it until a much higher temperature has been reached than is
necessary to cause reaction in free specimens.

On the other hand, both heat and cold interfere with this contact
reaction. Paramecia much above or much below the usual tempera-
ture do not settle against solids with which they come in contact, but
respond instead by a pronounced avoiding reaction. At a still higher
temperature even the avoiding reaction ceases. A Paramecium coming
against a solid presses the anterior end against it and continues to try to
swim forward, — succeeding only in revolving on its long axis (Massart,
IgOI @).

Specimens in contact with a solid react less readily to chemicals than
do free specimens, so that a higher concentration is required to induc:.

the avoiding reaction. On the other hand,

immersion in strong chemicals prevents see Si"
the positive contact reaction; Paramecia . O—
under such conditions coming against a .

solid react by the avoiding reaction. In Wascees
this case, then, the effect of the chemical

is to change the method of reacting to Fro. 66. — Pate ehiae beee
another stimulus —to the solid object. formed aring about a bubble of COs,
: : and have then come to rest against the
Certain other chemicals have the oppo- glass supporting rods, forming two
site effect, favoring the positive contact dense groups.
reaction. This is notably true of carbon dioxide. In water contain-
ing this substance the infusoria are strongly inclined to settle down
against any object with which they may come in contact. They thus
often form under these conditions dense masses attached to the glass
rods used for holding up the cover-glass (Fig. 66), though usually they
do not come to rest against smooth, hard objects.

94 BEHAVIOR OF THE LOWER ORGANISMS

The contact reaction may completely prevent the reaction to gravity.
Paramecia placed in a tube which contains many bits of solid matter, or
has its walls rough or dirty, usually do not rise to the top, but settle
against the solid matter on the wall and remain. They may thus re-
main scattered through all parts of the tube, or may gather in any por-
tion of it where the material inducing the reaction is found. Specimens
at rest against a solid may occupy any position with reference to gravity.
In similar ways the contact reaction may prevent the usual reaction
to water currents.

The interference between the contact reaction and the reaction to
the electric current produces a number of peculiar results. If a weak
electric current is passed through a preparation containing many speci-
mens attached to a bit of débris or to the surface of the glass, the free
specimens swim at once toward the cathode, while the attached speci-
mens do not react at all. If the current is made stronger, it produces
for an instant the usual effect on the cilia of the attached specimens.
The cathodic cilia strike forward, the anodic cilia backward. But this
does not continue; after a moment the contact reaction resumes its
sway, and the cilia have their usual positions. If the current continues,
after a short time the cilia are again affected as before; then resume
their original positions. This may occur many times, — the two stimuli
alternating in their control of the cilia. If the current is made much
stronger, the animal finally leaves the solid. It then swims directly
to the cathode in the usual way. To induce this reaction in a resting
specimen, it requires as a rule two or three times as intense a current as
that needed for producing the same effect on free swimming animals.

If the electric stimulus is first in action and the Paramecium then
comes in contact with a solid, somewhat different results are produced.
If the current is weak, often the animal, swimming toward the cathode,
ceases to react to the electricity on coming against the solid; it may
then take up any position on the surface of the solid. If it comes against
the surface film of the water, or the surface of the glass slide, it may
cease its forward movement only for an instant, then, becoming free, it
may swim again toward the cathode. If the current is a little stronger
(such as to produce the maximum rapidity of movement toward the
cathode, in free swimming specimens), a different effect is produced.
The Paramecium stops against the surface of the solid, and places itself
transversely or obliquely to the current, with the oral surface toward the
cathode (Fig. 67). Here it remains, the current produced by the cilia
being everywhere backward save in the oral groove, where it is forward.
If the electric current is reversed, the oral cilia strike strongly backward,
and the animal at once turns on its short axis till the oral surface

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 95

faces the new cathode. It remains in this position till the current is
reversed anew. Thus, when in contact with a surface, Paramecia often
show a transverse orientation with reference to the electric current. At
times the animal while in this position moves forward along the surface
with which it is in contact, transversely to the current; on reversal of
the current it turns about and moves in the opposite direction. This
may often be observed if the Paramecia are
placed on a slide in a thin layer of water
through which the electric current is passed.
Many of them in swimming come against
the glass or the surface film of the water.
Thereupon they begin to move transversely
to the current, as just described. Mean-
while the free swimming specimens con-
tinue to pass toward the cathode. +
Fic. 67. — Oblique position
With a stronger current a still different taken by Paramecium in contact with
effect is produced. The Paramecia are 2 Surface, when under the action of
s ; the electric current.
swimming forward in the slow, cramped
manner that is characteristic for strong currents. On coming in con-
tact with the surface film or the glass, the animals at once begin to
move backward (toward the anode) instead of forward. This con-
tinues as long as the contact continues. On becoming free they swim
forward again. ‘The reason for this behavior seems to be as follows:
In a strong electric current, as we know, the anterior cilia tend to drive
the animal backward, the posterior cilia forward (Fig. 62, 6); the latter
prevail. The contact reaction, as we have seen, causes the cilia behind
the region of contact to cease movement. When swimming forward
under the conditions mentioned, the Paramecia usually come in con-
tact with the surface at the thickest part of the body, near the middle
of its length. Thereupon, owing to the contact reaction, the cilia be-
hind this spot, driving the animal forward, cease to beat, while the cilia
in front, driving it backward, continue their action. Hence, the
anterior cilia gain the upper hand and force the animal backward.
Why does this contact stimulus thus interfere with the reaction to
other stimuli? There are two possible factors to be considered here,
one physical, the other physiological. The animal seems actually to
attach itself to solids, probably by a secretion of mucus. Such a secre-
tion is very evident in many infusoria, though it has not been demon-
strated in Paramecium. ‘This attachment would, in a purely physical
way, impede the movements due to other stimuli. While it is possible
that this factor may play a small part in the matter, it is clear that it is
not the important or essential factor. If it were, we should see the cilia

96 BEHAVIOR OF THE LOWER ORGANISMS

of the attached animal move in the usual manner under the influence of
stimuli, though these movements would not have the usual effect. Asa
matter of fact, in most cases we see nothing of the kind. The cilia
either do not move at all, or move in a manner different from that occur-
ring in free specimens. The essential factor in the interference is a
physiological one. When reacting to the contact stimulus, the animal
is less easily affected by other stimuli, and when reacting to the other
stimuli, it is less easily affected by the contact stimulus. Since the two
stimuli in question require behavior of opposite character, it is indeed
inevitable that one should give away to the other, or at least modify the
behavior toward it; both cannot receive the usual reaction.

Combinations of other stimuli have been less investigated than those
just considered. In any combination the reaction to gravity gives way,
as we have seen, to the reaction due to other factors. Paramecia swim-
ming upward react to other stimuli without hindrance, and Paramecia at
rest against a surface often show no orientation with reference to gravity.
The reactions to chemical and electrical stimuli completely supplant
the reactions to gravity. In a vertical tube Paramecia may form col-
lections in any region that becomes impregnated with carbon dioxide or
may avoid any region which contains a repellent chemical. If an elec-
tric current is passed through a vertical tube, the Paramecia react to it
in exactly the same manner as under other conditions, swimming toward
the cathode whether this is above or below. Sosnowski (1899) and
Moore (1903) have shown that many different stimuli modify the reac-
tion to gravity, changing the direction in which the animals swim. If
Paramecia in the culture fluid swim upward, mixture with tap water, or
with chemicals of various sorts, often causes them to swim downward.
This effect soon disappears, however, and the animals return to the top.
Increase of temperature to 30 degrees (Sosnowski), or decrease to 2 de-
grees (Moore), often has the same temporary effect. The same result
is at times produced by shaking or jarring the tube containing the ani-
mals; they go to the bottom, returning in a short time to the top. The
effect of all these agents varies with different cultures of Paramecia; in
some cultures the reaction to gravity is easily changed, in others with
difficulty or not at all.

Reactions to chemicals often interfere with the reaction to the
electric current. If through a preparation of Paramecia that are
gathered in an area containing carbon dioxide, as in Fig. 68, A, an
electric current is passed, the animals swim to the cathode side of the
area, then stop. All gather in this region, seeming to make vain efforts
to cross the invisible boundary (Fig. 68, B). Observation of individuals

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 97

shows that as soon as they reach the boundary:of the area of carbon
dioxide, they give the avoiding reaction, in the usual way, and pass back
into the area. Here they become oriented again by the electric current,
and pass again to the boundary, where they react as before. Thus the
reaction to the electric current prevails until a region of a sudden change
in chemical character is reached; the reaction to this then supplants
the reaction to the current. If the current is reversed, the animals
gather in the same way at the opposite side of the area of carbon dioxide
(Fig. 68,C). If the current is made very powerful and is long continued,

B\|- @ +

C | |+ }-

Fic. 68. — Interference of chemicals with the reaction to the electric current. At A Para-
mecia have gathered in an area containing COg. At B an electric current is passed through
the preparation with cathode at the left; the animals gather at the left edge of the area of COg.

At C the current has been reversed; the animals are therefore gathered at the right edge of the
area.

the Paramecia are one by one caused to cross the boundary of the acid
area and to swim to the cathode. If a drop of some repellent chemical
—as sodium chloride or an alkali —is introduced into a preparation
(Fig. 41), the Paramecia of course leave this vacant. If the electric
current is passed through the preparation, the Paramecia swim toward
the cathode; coming to the boundary of the drop, they swim around it,
leaving it empty, and thus reach the cathode. In this case the path
followed is a resultant of the operation of the two stimuli, — the orienta-
tion due to the electric current and the avoiding reaction produced by
the chemical.

If the entire region next the cathode is occupied by a repellent chemi-

svcalysthe Paramecia may be forced by a strong and long-continued cut-*

rent to enter it till they are destroyed.

A very peculiar interaction of chemicals and the electric current is

seen when Paramecia are placed in physiological salt solution (0.7 per
H

98 BEHAVIOR OF THE LOWER ORGANISMS

cent) and the current is passed through the vessel. The strong chemical
causes the animals to swim backward; the current orients them in the
usual way; the result is that they swim backward to the anode. This
phenomenon is to be observed in solutions of various chemicals, as
acids, potassium iodide, sodium carbonate, etc. It will probably be
found to occur in any solution that causes the animals to swim back-
ward for a considerable time. It should be investigated further. As
soon as the Paramecia have become accustomed to the chemical, so that
they no longer swim backward within it, they react to the current in the
usual way, swimming to the cathode.

Thus we find that under the action of more than one stimulus Para-
mecium may behave in any of the ways which we mentioned in our
first paragraph as conceivable. It may react to the first stimulus with-
out regard to the second, or to the second without regard to the first,
depending on which is the more effective. Such results are often pro-
duced when both the stimuli are sufficiently strong to cause reaction if
acting alone. Which stimulus shall produce its characteristic effect some-
times depends on which comes into action first. Thus, Paramecia in
contact may not react to the electric current or to heat; while free
Paramecia subjected to the same strength of current or degree of heat
do not show the positive contact reaction. This condition of affairs
seems to occur throughout the animal series; in higher animals we
express the same phenomenon subjectively by saying that attention to
one thing prevents attending to others.

In some cases the behavior shown is a resultant of the action of the
two stimuli. Examples of this are seen in the movement along a surface
under the simultaneous action of the contact reaction and a mechanical
shock, or in swimming around a chemical in solution, under the influence
of the electric current; or in swimming backward to the anode when in
solutions of strong chemicals.

Finally, the effect of one stimulus is sometimes merely to change
the method of reaction to another. Thus heat and strong chemicals
cause the animal to respond to contact by the avoiding reaction in place
of the positive contact reaction; carbon dioxide has the contrary effect.
The modifications of the reaction to gravity above mentioned are ex-
amples of the same thing. Cases of this character have much theoret-
ical interest. We shall return to them in considering the variability
and modifiability of the reactions of Paramecium.

2. VARIABILITY AND MODIFIABILITY OF REACTIONS

We have seen in the last section that the behavior of Paramecium
under a given stimulus may be determined by the simultaneous presence

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 99

of other stimuli. The behavior depends not only on the stimulus to
which it is primarily reacting, but also upon other external conditions.
May the nature of the behavior also depend upon internal conditions?
In other words, may the same animal under the same external conditions
behave differently at different times? May Paramecium, like higher
animals, become modified by the stimuli which it has received, or by
its own reactions, so as to react for the future in a manner different from
its reactions in the past?

It is difficult to obtain evidence on this question for Paramecium,
because the animal moves about so rapidly that it is hardly possible to
follow a given individual and determine whether its reactions do or do
not change. Much more is known in regard to this matter, as we shall
see later, for the fixed infusorian Stentor. But a number of significant
facts have been brought out for Paramecium.

First we have the fact that the presence of a certain agent or condi-
tion may alter the method of reaction to another. Paramecia in
heated water react to solids by the avoiding reaction in place of the
positive contact reaction; Paramecia in a solution of carbon dioxide,
on the other hand, are much more likely to respond by the positive
contact reactions. Many conditions — heat, cold, chemicals, mechani-
cal shock, etc. — alter, as we have seen, the reaction to gravity, causing
the animals to swim downward instead of upward. Such phenomena
indicate that the first agents alter in some way the physiological con-
dition of the animals, so that they now react to the second agent in a
changed manner. This conclusion is impressed upon the observer
by the behavior of the organisms. Specimens in heated water are
swimming about violently, so that we should not expect them to come
to rest against solids. Those in carbon dioxide move slowly and seem
in a condition predisposing to repose, so that coming to rest against
solids is the reaction that might be anticipated. The interference
between the two stimuli is not purely physical. There is nothing in the
physical action of heat or a mechanical jar to make the animals move
downward, as happens when the agents reverse the action to gravity.
Indeed, in the latter case one can plainly see that the downward move-
ment is an active one. The only explanation possible for such cases
is that the animals have become changed in some way by the first stimu-
lus, so that they now react in an altered manner to the second stimulus.

Further we find that there are great differences in the reactions of
different individual Paramecia, and especially of Paramecia from
different cultures. In studying the reactions to chemicals, one often
finds that a few individuals swim directly into the given solution, while
the majority give the avoiding reaction on coming in contact with it,

100 BEHAVIOR OF THE LOWER ORGANISMS

and hence remain outside (Jennings, 1899 ¢, p. 373). While in a cer-
tain case individuals from one culture were repelled by #5 per cent lithium
chloride, those from another culture were found to be quite indifferent
to a solution of the same chemical sixteen times as strong, swimming
readily into a drop of % per cent lithium chloride (Jennings, 1899 c,
p- 374). When placed in a vertical tube, Paramecia from certain cul-
tures gather at the top; from other cultures at the bottom; while in
other cases they remain scattered throughout the tube (Sosnowski,
1899). Corresponding variations are found in the reaction to water
currents. Similar differences are to be observed with regard to the
positive contact reaction (Piitter, 1900, p. 253). Infusoria in certain
cultures are strongly inclined to attach themselves to solids, forming
dense masses on the surface; in other cultures such masses are never
formed. In fresh cultures the animals are usually much inclined to
attach themselves in this way; in old cultures they are not. Even in
a culture where most of the animals attach themselves, there are always
a number of specimens which remain persistently free. Variations are
to be observed at times in the reactions to electricity ( Jennings, 1904 h).
One sometimes observes that while most of the specimens in a prepara-
tion are reacting to the electric current in a precise way, a few speci-
mens do not react at all, swimming about at random. Sometimes
single specimens will be seen swimming toward the anode, while all the
rest'swim toward the cathode. This is most often observed after the
current has been reversed several times.

Whether the variations mentioned in the last paragraph are due to
changes which have occurred during the life-time of the animals, or
whether they are permanent differences between different individuals
we do not know. In either case they.are of importance, since they give
much opportunity for the action of natural selection. This is a point
to which we shall return later.

We know, however, that sometimes the behavior of the same indi-
vidual varies, and in some cases we can form an idea of the nature of
the change which has occurred. If a Paramecium is subjected to a
strong induction shock, it fails for some time thereafter to react to weak
shocks, though at the beginning it reacted to these (Statkewitsch, 1903).
This result is probably due to a change in the animal such as we com-
monly call fatigue. To be explained possibly in a similar way is the
following occasional observation. A specimen in the continuous elec-
tric current is swimming toward the cathode; on reversal of the current
it retains its orientation and continues to swim forward, — now of
course toward the anode. This lasts usually but a short time.

Paramecia which have been living at the usual temperatures show

THE BEHAVIOR OF INFUSORIA; PARAMECIUM ‘IOI

a temperature optimum of about 24 to 28 degrees; if they are kept for
‘some hours at a temperature from 36 to 38 degrees, the optimum rises
to 30 or 32 degrees (Mendelssohn, 1902). A change in the individuals
induced in this way is commonly spoken of as acclimatization. Simi-
lar changes could doubtless be induced in the reactions to chemicals
and to other stimuli; this has not yet been done.

Paramecia that have long been deprived of food behave in a some-
what different manner from normal individuals (Moore, 1903; Wal-
lengren, 1902 a). But the changes in behavior are apparently due to
actual structural changes in the organism, due to lack of food, and render-
ing it impossible for the animal to move so strongly and rapidly (Wal-
lengren, 1902 a). Paramecia kept in distilled water are found to be
much more sensitive to most stimuli than usual (Jennings, 1897; Wal-
lengren, 1902 @); owing apparently to lack of sodium salts in the body.
This condition may perhaps be called that of salt hunger. If a small
quantity of some sodium salt is added to the distilled water, the Para-
mecia return to the usual condition (Wallengren, rgo2 a).

Certain changes in the behavior of individuals can hardly be classi-
fied as due either to fatigue, acclimatization, or hunger. If a bit of
filter paper is placed in a preparation of Paramecia, the following be-
havior may often be observed. An individual swims against it, gives
the avoiding reaction in a slightly marked way, swimming backward
a little; then it swims forward again, jerks back a shorter distance,
then settles against the paper and remains. After remaining a few
seconds, it may move to another position, still remaining in contact
with the paper. Then it may leave the paper and go on its way. All
this may happen without the slightest evident change in the outer con-
ditions. So far as can be seen, the Paramecium first responds to the
solid by the avoiding reaction, later by the positive contact reaction,
and still later suspends the contact reaction, all without any change in
external conditions. The changes inducing the change in reaction must
then be within the animal.

Again, as we have seen, jarring Paramecia which have collected at
the top of a tube often causes them to swim to the bottom of the tube
(Sosnowski, Moore). The jarring itself lasts but a moment, while
the Paramecia continue for some time after to swim downward. The
shock must therefore have changed the physiological condition of the
animals, so that they now show a change of reaction to gravity, or
possibly a lack of reaction to gravity.’

‘It is possible that the shock merely causes them to swim rapidly in any direction
that is open to them. Since they are already at the top of the tube, the only direc-
tion open to them is that leading downward.

102 BEHAVIOR OF THE LOWER ORGANISMS

All together, it is clear that there are differences in behavior due to
differences in the internal or physiological condition of the animal, —
differences shown even in a single individual at different times. Some
of the different physiological conditions may be characterized as fatigue,
as acclimatization, as hunger, or the like. In other cases they cannot
be definitely characterized. We clearly have slight beginnings of the
modification of behavior through the previous experiences of the organism.
The analysis of this matter will be carried farther. for the behavior of
unicellular organisms in the account of Stentor (Chapter X).

3- BEHAVIOR IN FISSION AND CONJUGATION

At intervals certain extraordinary episodes connected with the pro-
cesses of reproduction interrupt the usual life of Paramecium. The
behavior at such times seems not to differ in any notable manner from
the usual behavior. We shall therefore describe it only briefly.

Fission. — At times the animal begins to divide into two by a trans-
verse constriction at about the middle. During the early stages of the
process the two halves act in unison. The currents
of water are driven by the cilia in the same direction
over both, and the two halves react to any stimulus
as a single animal. _ If subjected to induction shocks
the half at the anode responds by contraction of the
ectosarc and discharge of trichocysts, while the
cathode half does not. As the constriction sepa-
rating the two halves becomes very deep, so that they
are connected only by a slender strand, they begin
to behave more independently. The anterior half

Fic. 69.—A pair t times changes its direction of movement, while the
of conjugating Para- posterior half tries to continue straight forward. The
te connecting strand is strained and bent or twisted.
Soon it breaks, and the two individuals are separated.

Conjugation. —In conjugation two individuals become united by
their oral surfaces (Fig. 69), and a complicated process of interchange
of nuclei occurs. The union of two specimens seems brought about
chiefly by the usual movements and reactions of the animals, taken in
connection with a physical change of the body substance in the region
of the oral groove. Here the surface becomes viscid, so that if another
Paramecium comes in contact with this region, the two stick together.
- Often two individuals may be seen at rest close together on the surface
of a bit of bacterial zodgloea. One drags its posterior end across the
oral groove of the other, whereupon the two stick together (Fig. 70, @).

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 103

Each tries to continue its course, so that they pull in opposite directions.
One may drag the other along with it, or the two may finally pull apart.

There is of course a tendency for objects to be brought against the
oral groove, owing to the strong current of water that passes along this
region; it is through this fact that Paramecium gets its food (compare
Fig. 46). This tendency operates on other Paramecia in the neigh-
borhood as well as on inanimate objects. If two Paramecia are close
together with oral grooves facing each other (Fig. 71), this tendency is
reciprocal; each tends to draw the other to its own oral surface. On

Fic. 70. — Groups of individuals adhering to each other by their oral surfaces, from cultures
of Paramecia undergoing conjugation. a, Two attached individuals swimming in opposite
directions. 6, Three individuals attached by their oral surfaces to a fourth. c, Three indi-
viduals irregularly attached. d, A conjugating pair, swimming to the left, with a third individual
attached by its oral surface to the posterior part of one of these, and a fourth individual trans-
versely attached to the third. The third and fourth were dragged about by the first pair.

the other hand, if the aboral surfaces face each other, the currents tend
to separate the two Paramecia. Hence when two Paramecia come in
contact it will usually be by the oral surfaces. This often happens under
usual conditions, but no conjugation results, because the oral surfaces
have no tendency to adhere; the animals therefore quickly separate
again. But at times when the oral surfaces are viscid, specimens which
come thus in contact remain united. The succeeding internal processes
fall in the field of physiology rather than that of behavior. Details
concerning them will be found in text-books of zodélogy.

Thus nothing seems to be required for producing conjugation be-
yond the usual movements and the viscidity of the oral region. The

‘104 BEHAVIOR OF THE LOWER ORGANISMS

present author has been unable, after careful study, to detect any differ-
ences in the methods of reacting during periods of conjugation. The
groups formed on the surface of solids and the rapid movements of the
organisms, described by Balbiani (1861, p. 441), as occurring at such
periods, are by no means peculiar to conjugat-
ing infusoria. They take place in the same
manner in cultures where none are conjugating.

The significant part played in conjugation by
the viscidity of the oral surfaces is demon-
strated by the peculiar phenomena observed
when specimens accidentally come in contact
irregularly. This often happens where the ani-
mals.are numerous. If any part of the body of
‘one specimen comes by chance against the oral
surface of another, the two stick together, with-
out regard to their relative position.

Often groups of three or four or more are

Fic. 71.— Currents urging 2 ‘ : es
two Paramecia together when formed in this way (Fig. 70). The individuals

the oral sides face one another. o-cypy all sorts of irregular positions, and each

endeavors to swim forward in his own direction. Some are pulled back-
ward, others sidewise, against their vigorous struggles. Often one suc-
ceeds in freeing itself, and then swims away; others remain caught in
such groups indefinitely. Even moribund specimens and specimens
undergoing fission sometimes thus become united irregularly with
others. But the regular union of individuals by the oral surfaces is
more common than the formation of irregular groups, owing to the
strong tendency, produced by the usual currents, for Paramecia to come
together at the oral surfaces.

During conjugation the two united individuals behave in much
the same way as a single specimen. They revolve on the long axis to
the left as they swim through the water, and they react to stimuli by the
avoiding reaction in the usual way. The direction of turning in the
avoiding reaction seems determined usually by one of the components;
the pair always turn toward the aboral side of this particular individual.
If subjected in the transverse position to an induction shock, only the
specimen next the anode responds by ejecting trichocysts (Statkewitsch,
1903).

4. THE DAILY LIFE OF PARAMECIUM
Let us now try to form a picture of the behavior of Paramecium in

its daily life under natural conditions. An individual is swimming
‘freely in a pool, parallel with the surface and some distance below it.

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 105

No other stimulus acting, it begins to respond to the changes in distri-
bution of its internal contents due to the fact that it is not in line with
gravity. It tries various new positions until its anterior end is directed
upward, and continues in that direction. It thus reaches the surface
film. To this it responds by the avoiding reaction, finding a new posi-
tion and swimming along near the surface of the water. Now there
is a strong mechanical jar, — some one throws a stone into the water,
perhaps. The Paramecium starts back, tries certain new directions,
and finishes by reacting to gravity in the reverse way from its former
reaction; it now swims downward. But this soon brings it into water
that is notably lacking in oxygen. To this change it responds as be-
fore, trying new directions till it has come near the surface again. Swim-
ming forward here, it approaches a region where the sun has been
shining strongly into the pool, heating the water. The Paramecium
receives some of this heated water in the current passing from the
anterior end down the oral groove. Thereupon it pauses, swings its an-
terior end about in a circle, and finding that the water coming from one
of the directions thus tried is not heated, it proceeds forward in that
direction. This course leads it perhaps into the region of a fresh plant
stem which has lately been crushed and has fallen into the water. The
plant juice, oozing out, alters markedly the chemical constitution of
the water. The Paramecium soon receives some of this altered water
in its ciliary current. Again it pauses, or if the chemical was strong,
swims backward a distance. Then it again swings the anterior end
around in a circle (Fig. 38) till it finds a direction from which it receives
no more of this chemical; in this direction it swims forward.

Thus the animal swims about, continually hesitating as it reaches
regions where the conditions differ, trying new directions, and changing
its course frequently. Every faint influence in the water affects it,
for the animal is very sensitive. Other Paramecia swim about in the
same way. They do not avoid each other, but often strike together;
then one or both draw back and turn in another direction. The animal
may strike in the same way against stones or the sides of a glass vessel.
In such cases it may be compelled to try successively many different
directions before it succeeds in avoiding the obstacle, — acting like a
blind man who finds a stone wall in his course. .

After a time our animal comes against a decayed, softened leaf.
At first it draws back slightly, then starts forward again, and places
itself against the leaf. The body cilia cease their action, while the oral
cilia carry a strong stream of water to the mouth. It so happens that
this leaf has lately fallen into the water and has no bacteria upon it, so
that the Paramecium receives no food. Nevertheless the animal “‘tries”’

106 BEHAVIOR OF THE LOWER ORGANISMS

it for a while. Other Paramecia may gather in the same way, but after
a considerable time they one by one leave the dead leaf. Our Para-
mecium swims about again, being directed hither and thither by the
various changes in the chemical constitution or temperature of the water,
till it comes to a region containing more carbon dioxide in solution than
usual. It gives no sign of perceiving this, save perhaps by swimming
a little less energetically than before. The area containing carbon
dioxide is small, and soon the animal comes to its outer boundary,
where the water drawn to its oral groove contains no carbon dioxide.
It stops, and tries different regions, by swinging its anterior end around
in a circle, till it again finds a direction from which it receives carbonic
acid; in that direction it swims forward. Since it behaves in the same
way whenever it comes to the outer boundary of the carbonic acid, it
remains swimming back and forth within this region, and thus in time
explores it very thoroughly. Finally it comes upon the source of the
carbon dioxide, — a large mass of bacteria, embedded in zodgloea, that
are giving off this substance. The infusorian places itself against the
mass of zodgloea, suspends the activity of the body cilia, and brings a
strong current of water along the oral groove to the mouth. This current
removes some of the bacteria from the zoégloea and carries them to the
mouth, where they are swallowed. While the animal is thus occupied,
other Paramecia in their headlong course may strike against it. But
now it does not react to such a shock at all; it remains in place, engaged
with its food taking. After the animal has been in this position for some
time, the sun begins to shine strongly on this part of the pool, heating
the water. All the free-swimming Paramecia in this region thereupon
begin to swim rapidly about, repeatedly backing and trying new direc-
tions, till a direction is found that leads to a cooler region. But our
Paramecium, busy with its food-getting, does not react to the heat at
all. The water becomes hotter and hotter, and after a time our infuso-
rian moves about a little, turning over or shifting its position, but still
remaining against the zodgloea. All the free swimming specimens have
left this region long ago. As the water becomes still hotter, our Para-
mecium suddenly leaves the mass of zodégloea and now dashes about
frantically under the influence of the great heat. It first swims back-
ward, then forward, and tries one direction after another. Fortunately
one of these directions soon lead it toward a cooler region. In this
direction it continues and its behavior becomes more composed. It
now swims about quietly, as it did at first, till it finds another mass of
bacteria and resumes the process of obtaining food.

In this way the daily life of the animal continues. It constantly
feels its way about, trying in a systematic way all sorts of conditions,

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 107

and retiring from those that are harmful. Its behavior is in principle
much like that of a blind and deaf. person, or one that feels his way
about in the dark. It is a continual process of proving all things and
holding to that which is good.

5. FEATURES OF GENERAL SIGNIFICANCE IN THE BEHAVIOR OF
PARAMECIUM

A. The Action System

Passing in review the behavior of Paramecium, we find that the
animal has a certain set of actions, by some combination of which its
behavior under all sorts of conditions is made up. The number of
different factors in this set of actions is small, and they are combined
into a codrdinated system, so that we may call the whole set taken
together the action system. The action system of Paramecium is based
chiefly on the spiral course, with its three factors of forward movement,
revolution on the long axis, and swerving toward the aboral side. The
behavior under most conditions is determined by variations in these
three factors. Such variations, combined in a typical manner, produce
what we have called the avoiding reaction. Other elements in the action
system are the resumption of forward movement, in response to stimula-
tion, and the coming to rest against solid objects in what we have called
the positive contact reaction. Subordinate activities, playing little part
in the behavior, are the contractions of the ectosarc and the discharge
of trichocysts. .

The action system thus includes only a small number of definite
movements. By one or another of these, or by some combination of
them, we may expect the organism to respond to any stimulus which
acts upon it. We cannot expect each kind of stimulation to have a
specific effect, different from that produced by other stimuli, for all
any stimulus can do is to set in operation certain features of the action
system. Many different stimuli acting on this one organism therefore
necessarily produce the same effect. Different organisms have different
action systems, so that the same agent acting on different organisms may
produce entirely different effects. ‘The nature of the behavior under
given conditions depends as much (or more) on the action system of the
animal as on the nature of the conditions. In studying the behavior
of any organism the most important step is therefore to work out its
action system, —the characteristic set of movements by which its
behavior under all sorts of conditions is brought about.

The most important features of the action system of Paramecium

108 BEHAVIOR OF THE LOWER ORGANISMS

are those shown in what we have called the avoiding reaction. This,
as we have seen, consists essentially in reversing, stopping, or slowing
up the forward motion, then swerving more than usual toward the aboral
side, while at the same time the rate of revolution on the long axis is
decreased. By this combination of movements Paramecium responds
to most effective stimuli that act upon it. By it are produced both
negative and positive reactions.

B. Causes oj the Reactions, and Effects produced by them

Examination has shown us that the cause for this reaction is some
change in the conditions; usually some change in the relation of the
animal to the environmental conditions. Such changes are brought
about chiefly by the movements of the animal. In certain cases
they are due to the direction of movement, carrying the animal into
environmental conditions which stimulate it; in other cases they are
due to the axial position taken by the animal, this resulting in internal
or external disturbances which act as stimuli.

These stimuli produce, as we have seen, not a single, simple, definitely
directed movement, comparable to the typical reflex act. On the con-
trary, stimulation is followed by varied movements, made up of several
simultaneous or successive factors, each of which may vary, as we have
seen in detail, more or less independently of the others. These move-
ments produce varied effects, as follows: (1) They place the animal
successively and in a systematic way in many different axial positions
(see Fig. 38); (2) they cause it to move successively and systemati-
cally in many different directions; (3) they subject it successively
to many different environmental conditions, — of temperature, light,
chemicals, mechanical stimuli, etc. Now, it is evident that in this way
the animal is practically certain to reach finally a position, direction of
movement, or environmental condition, that removes the cause of stimu-
lation, since the latter was due to something wrong in one of these
respects. The reaction then ceases, since its cause has ceased; the
animal therefore retains the axial position, direction of motion, or en-
vironmental condition thus reached. The method of reaction is then
of such a character as to bring about whatever is required for putting
an end to the stimulation, — whether this requirement is one of orienta-
tion, of general direction of locomotion, or of the retention of certain
environmental conditions.

Thus the behavior and reactions of Paramecium consist on the whole
in performing movements which subject the organism to varied condi-
tions (using this word in the widest sense), with rejection of certain of these

THE BEHAVIOR OF INFUSORIA; PARAMECIUM 109g

conditions, and retention of others. It may be characterized briefly
as a Selection from among the varied conditions brought about by varied
movements.

The fundamental question for this method of behavior is, Why does
the organism reject certain conditions and retain others? We find
that the animal rejects, on the whole, such things as are injurious to it,
and accepts those that are beneficial. There are perhaps some excep-
tions to this, but these are rare and only noticeable because exceptional;
in a general view the relation of rejection and acceptance to injury and
benefit is evident. It results in keeping the animals from entering
temperatures that are above or below those favorable for the life pro-
cesses, in causing them to avoid injurious chemicals of all sorts, in saving
them from mechanical injuries, and in keeping them in regions con-
taining food and oxygen. Clearly, the animal rejects injurious things,
and accepts those that are beneficial.

How does this happen? We meet here the same question that we -
find in higher organisms and man. How does it happen that in man
the response to heat and cold beyond the optimum is by drawing back,
just as it is in Paramecium? How does it happen that in both cases
there is a tendency to reject things injurious and retain things bene-
ficial? We shall attempt in a later chapter to bring out the relations
involved in this problem, in such a way as to make it possibly a little
more intelligible; here we shall content ourselves with pointing out
the identity of the problem in the infusorian and in man.

LITERATURE VI

; A. Interference between contact and other stimuli: PUTTER, 1900; JENNINGS,
1897, 1904 h.

8. Heat and other stimuli: MENDELSSOHN, 1902 a; MASSART, Igo! a.

C. Gravity and other stimuli: SosNowsKI, 1899; MOORE, 1903.

D. Behavior in conjugation: JENNINGS, 1904 4; BALBIANI, 1861.

CHAPTER VII
THE BEHAVIOR OF OTHER INFUSORIA

AcTION SYSTEMS. REACTIONS TO CONTACT, TO CHEMICALS, TO HEAT
AND COLD

THE infusoria form a large and varied group of organisms. In
the present chapter we shall try to show-how far the behavior of Para-
mecium is typical for the group, and to bring out important differences
found in the behavior of other species. Certain features of behavior
are better illustrated in other infusoria than in Paramecium; these we
shall treat in detail. This is notably true of the reactions to light, and
to a less degree of the reactions to certain other stimuli. Certain
infusoria are much more favorable for a study of the modifiability of
reactions than Paramecium, so that we shall examine these relations
with care.

I. THE ACTION SYSTEM

We found that Paramecium has a certain set of ways of acting, —
of “habits,” one might call them, — of which its behavior under most
conditions is made up. ‘These are few in number and combined into
a connected system, which we have called the ‘“‘action system.” The
action system of Paramecium is typical of what we find throughout the
infusoria, including both the flagellates and the ciliates. But it becomes
modified among different species, in accordance with their varying
structure and the conditions under which they live. Practically all the
infusoria agree with Paramecium in swimming in a spiral when passing
freely through the water, and in the fact that when stimulated they
turn toward a certain side, defined by the structure of the organism.
But some species instead of swimming freely usually creep along sur-
faces, while others are attached by one end to solid objects, remaining
‘in the same spot indefinitely. These different methods of life neces-
sitate changes in the action system. We shall take up briefly a number
of species, bringing out the essential features of the action system.

IIo

THE BEHAVIOR OF OTHER INFUSORIA IIl

A. Flagellata

The free swimming flagellates move in a spiral, keeping a certain
side of the body always toward the outside of the spiral,’ just as Para-
mecium does. By means of the flagella they draw a cone of water from
in front to the anterior end of the body, as happens in Paramecium.
Among the flagellates the behavior has
‘been most precisely studied in Chilomonas
and Euglena (Jennings, 1900, Ig00 @
and 6).

Chilomonas. — Chilomonas is an un-
symmetrical organism, of an irregularly
oblong form. ‘The body is compressed
sideways and bears an oblique notch at the
broader anterior end (Fig. 72). Of the two
anterior angles which lie on either side of
the notch, one (x) is larger and lies more
to the right than the other (y). From the
notch arise two long flagella, by the aid of
which the animal swims. Chilomonas
often occurs in uncounted millions in water
containing decaying vegetation.

In swimming, Chilomonas revolves on
its long axis, at the same time swerving Fis. i. Clillomoae ado det
toward the smaller of the two angles at <. v., contractile vacuole; f, flagella;
the anterior end (Fig. 72, y). The path & pale pe —. slays or
followed thus becomes a spiral (Fig. 73).

The animal often comes to rest against solid objects; it is then attached
by one of the two flagella, while the other is free.

To most effective stimuli Chilomonas responds by an avoiding re-
action similar to that of Paramecium. Its forward movement becomes
slower, ceases, or is transformed into a movement backward. Then
the animal turns more strongly toward the side which bears the smaller
angle, and finally starts forward again. Thus the path is altered. The
reaction consists essentially in pointing the anterior end successively in
many directions, toward one of which the animal finally swims. The
different factors in the reaction vary with the intensity of the stimula-
tion, just as they do in Paramecium. The reaction may be repeated,
as in the animal last named, until it finally carries the organism away
from the stimulating region. Thus it is clear that in Chilomonas, as in

1 This was first observed by Naegeli (1860),

112 BEHAVIOR OF THE LOWER ORGANISMS

Paramecium, the method running through the behavior is that of the

selection of certain conditions through the production of varied move-

ments. When stimulated the animal “tries’? many different directions

till one is found in which stimulation

ceases. This reaction is known to be pro- !

duced in Chilomonas by heat, by the

drying up of the water containing the d

animals, by mechanical stimulation, by

various chemicals, by passage from water

containing certain chemicals (acid) to water

containing none, and by the electric cur-

rent. We shall take up certain details of

the reactions of Chilomonas in the sec-

tions which deal with the

different classes of stimuli.
Euglena. — Euglena

viridis (Fig. 74), like

Chilomonas, swims in a

spiral. The larger lip

ones Sex J (Fig. 74, x) is always

BA: toward the outer side of .

the spiral (Fig. 94).

When stimulated by com- b

ing in contact with a weak

chemical, by a mechanical

shock, or by a change in ‘

the intensity of light, Eu- \

glena responds by an \

avoiding reaction similar

to that of Paramecium

and Chilomonas. The
Fic. 74. — Ew forward motion becomes

glena viridis, after

Kent. ¢. v., reservoir Slower, ceases, or (more

Ot octane rarely) ff transformed Fic. 73. — Spiral path of

gullet; nu, nucleus; x, into a backward motion. Chilomonas. 4, }, ¢, d, suc-

larger or upper lip. Then the organism cessive positions occupied. /

swerves more strongly than usual toward the larger lip. Thus the

spiral becomes wider and the organism becomes pointed successively

in many directions (see Fig. 91). In one of these directions it finaly

swims forward, repeating the reaction if again stimulated. We shall

have occasion to describe in detail the reactions of Euglena to light

(Chapter VIII).

-
8 a oe

THE BEHAVIOR OF OTHER INFUSORIA 113

To most very intense stimuli Euglena responds by contracting into
a sphere and beginning to encyst.

The behavior of most other flagellates is not known in detail, since
the organisms are usually very minute and their precise movements can
be followed only with much difficulty. Cryptomonas ovata is known to
respond to stimuli in essentially the same way as Euglena (Jennings,
1904 @), —the swerving being toward the more convex surface. The
flagellate swarm spores of various alge react in much the same way, as
is shown by the descriptions of Naegeli (1860) and Strasburger (1878),
though the precise details have not been worked out as they have for
Chilomonas, Euglena, and Cryptomonas. Naegeli (/. c.,p. 101) describes
the behavior of the flagellate swarm spores on coming against a mechani-
cal obstacle, as follows: They swim backward, turn to one side, then
swim forward in the changed direction. This is exactly what Chilo-
monas does, as we have seen. Similar observations have been made
on flagellates by various investigators, but only in the species we have
named has the side toward which the organism turns been determined.

B. Ciliata

In many free swimming ciliates the action system is known to be
essentially similar to that of Paramecium. All swim in spirals, swerv-
ing toward a certain side, and react to stimuli by backing and swerving
more than usual toward a structurally defined side. Loxodes rosirum

fe eas Oe
a Cf Ge

Fic. 75.— Reaction of Loxo- Fic. 76.— Methods of reaction to strong stimuli
phyllum meleagris. 1-4, succes- in Stentor. The individual at 1 is stimulated; it there-
sive positions. upon swims backward (2, 3), turns toward the right

aboral side (3, 4), and swims forward (5).

in reacting turns toward the aboral side. Loxophyllum meleagris re-

acts as a rule by turning toward the oral side (Fig. 75). Stentor poly-

morphus, Stentor ceruleus, and Stentor reselit (Fig. 31, 6), when free

swimming, react by turning toward the right aboral side (Fig. 76). Bur-

saria truncatella reacts to most stimuli by swimming backward and
T

9 ee BEHAVIOR OF THE LOWER ORGANISMS

turning toward the right side (Fig. 77). Spirostomum ambiguum and
Spirostomum tenue swim backward and turn toward the aboral side.
Opalina ranarum turns toward the more convex (right) side, Nycto-

\ therus toward the aboral side
(Fig. 78). . Many of these or-
ganisms show an _ additional
- reaction to strong stimuli, con-
sisting in a marked contraction
of the body. This is particu-
larly noticeable in Spirostomum
and Stentor.

Many of the Ciliata do not
as a rule swim freely through
the water, but creep along sur-
faces, keeping one side against

Fic. 77. — Reaction of Bursaria, ventral view. the surface. This is true at
Faas peeepere pomcions occupied. times of most of the organisms
mentioned in the foregoing paragraph. It is much more usual in cer-
tain other ciliates, belonging to the group of Hypotricha (Fig. 31, /;
Fig. 81). In these animals the cilia of one side of the body are spe-
cially modified for creeping, while the opposite side
bears either few and weak cilia or none at all. The
Hypotricha are usually found running about on the
bottom, or on the surface of objects in the water.
In addition to their creeping movements, they pro-
duce by means of strong peristomal cilia a vortex
leading back to the mouth. These animals of course
do not revolve on the long axis as they progress, and
the corresponding feature is likewise lacking in the
reactions to stimuli. On coming in contact with an
obstacle, or when otherwise stimulated, they stop or , F's- 78-— Nycto-

, therus. The arrow to
move backward a distance, then turn toward a cer- the right shows the
tain structurally marked side, keeping in contact with ‘rection of turning in

‘ . Yesponse to stimula-

the substratum and not revolving on the long axis. tion, while the three

This renders it much easier to observe the precise iterior arrows indicate

‘ * . the direction of beat of

method of reacting than in Paramecium, where the the cilia. After Dale
rapid revolution on the long axis is very confusing. 9°").

As examples of the creeping infusoria, the following may be mentioned :—

Stylonychia (Fig. 31, f), Oxytricha, and other Hypotricha react to
‘most stimuli by moving backward and turning to the right (Fig. 79).
These organisms are particularly favorable for the study of the reaction
method. The body is flat, and the right and left sides are very easily

THE BEHAVIOR OF OTHER INFUSORIA 115

distinguished, so that the direction of turning after stimulation can be
determined with the greatest ease. In many respects the Hypotricha
are among the most favorable objects to be found among unicellular
animals for studying behavior.

Microthorax sulcatus usually creeps along the bottom, and reacts to
most stimuli by turning suddenly toward the convex (“dorsal’’) edge.
The turning may or may not be
preceded by a start backward.

Colpidium colpoda (Fig. 31,
d) usually moves forward with
one side against the substratum,
following a curve with its oral
edge on the concave side of the
curve. When stimulated me-
chanically or chemically, it turns
toward the aboral side and con- _ Fic. 79.— Reaction of Oxytricha, ventral
tinues its course (Fig. 80). MEN 2 OO

In some cases the reaction to strong stimulation takes on special
features. For example, in Plewronema chrysalis, in Halteria grandi-
nella, and in various Hypotricha, there are powerful bristle-like cirri,

by means of which the animal

| ne may leap suddenly backward
fort or to one side. These are
¥, Ane 4 bie probably to be considered
¢ ‘
2 * 1

strongly marked avoiding re-
actions, not differing in prin-
ciple from what we find in
Paramecium or Oxytricha.
Fic. 80.— Path of Colpidium. At 2 it is All the species which usu-
slightly stimulated; it thereupon turns toward the ally move along on a surface
aboral side (3-4) and continues its curved course. ° .
may at times swim freely
through the water. They then as a rule revolve on the long axis, both
when progressing and in the avoiding reaction. On the other hand,
almost all the species which characteristically swim freely through the
water do at times move along surfaces. They may then react to
stimuli in the same way as do the Hypotricha. Such forms as Bursaria
and Loxophyllum are transitional between the free swimming species
and those that creep along surfaces; they are found about as often in
-one situation as in the other.
In the Ciliata thus far considered the reaction method is evidently
that of the selection of certain environmental conditions through the
productions of varied movements. When its movement leads to stimu-

116 BEHAVIOR OF THE LOWER ORGANISMS

lation, the animal responds by trying many new directions, till one is
found which does not lead to stimulation. The reaction is less flexible
in the ciliates which creep along surfaces than in the free swimming
ones. In the former, owing to the lack of revolution on the long axis,
all the directions tried lie in a single plane. But under many powerful
stimuli even these species usually leave the surface on which they are
moving; they then react in the freer way characteristic of unattached
organisms, trying directions lying in many different planes.

There exists also a large number of ciliates which become more or
less permanently attached by the part of the body opposite the mouth.
This attached portion is usually drawn out to form a slender stalk or
foot. Examples of such infusoria are Stentor (Fig. 31, b) and Vor-
ticella (Fig. 31, c). Some of these species are found attached under
all usual conditions; such are Vorticella and Carchesium. Others are
frequently found swimming freely; this is the case, for,example, with
Stentor ceruleus. Some infusoria become fixed in only a temporary
way, by a mucous secretion. Such are Spirostomum and Urocentrum,
which are often found suspended from solid objects by a thread of
mucus (Fig. 82). Even the species which are most firmly fixed may
under powerful stimuli detach themselves and swim away. The heads
of Vorticella and Carchesium thus at times detach themselves from their
stalks and swim about like Paramecium. At such times they may also
creep over surfaces, just as do the Hypotricha. The behavior when free
is essentially similar in its main features to that of Paramecium or
Oxytricha.

In the attached condition the mouth and peristome are usually
above, surrounded by a wreath of large cilia. These cilia are in con-
tinual movement, in such a way as to bring a current of water from above
to the mouth. Some fixed infusoria contract at intervals with marked
regularity, even when there is no external stimulation. Such is the case
in Vorticella. The reactions to stimuli are much modified as compared
with those of the free swimming species. The avoiding reaction be-
comes broken up into a number of factors, any one of which may take
place more or less independently of the others. Thus, Stentor reselii
may respond to stimulation either by a reversal of the cilia, driving away
the water currents, by bending over toward the right aboral side, or by
withdrawing into its tube. Each of these reactions corresponds to a
certain definite feature in the avoiding reaction of free infusoria. Owing
to the disintegration of the avoiding reaction into independent parts, the
behavior of these fixed infusoria become more varied and more highly
developed than that of the unattached species. We shall have occasion
to treat of this in detail later, in our account of the modifiability of
reactions in Protozoa.

THE BEHAVIOR OF OTHER INFUSORIA 127

2. REACTION TO MECHANICAL STIMULI

In the responses of infusoria to contact with solid objects we may
distinguish the same two reaction types that we found in Paramecium.
The animal may react in what might be called a “negative’’ way, avoid-
ing the object, or it may react “positively,”’ placing itself against the
solid body.

The negative response to contact with solid bodies is the typical
“avoiding reaction.” The animal moves backward, turns toward a cer-
tain definite side, then swims forward again. In other words, it tries
a new direction. If this leads again against the obstacle, the animal
again reacts in the same way, and this is repeated, till through frequent
trials the obstacle is avoided.

There are certain important points regarding the relation of the direc-
tion of movement in this avoiding reaction to the part of the body that is
stimulated. Since the animal usually swims forward under natural con-
ditions, it will as-a rule come in contact with large solid objects at its
anterior end. Further, small objects may be carried by the ciliary cur-
rents to the oral side. Thus the movement backward and the turning
toward the aboral side in the avoiding reaction remove the animal from
the source of stimulation. But experimentally other parts of the body
can be stimulated. Thus in Oxytricha (Fig. 79), we may with the tip
of a fine glass rod stimulate either the left (oral), or the right (aboral),
side. In either case the animal backs and turns to the right. If the
right side is repeatedly stimulated, the animal continually wheels toward
the stimulated side; if the left side is touched, it wheels continually
away from the stimulated side. Thus the direction of movement in the
reaction is not determined by the side stimulated, but by the structural
relations of the organism. On the other hand, if we stimulate the
posterior end sharply, the animal does not respond by the typical avoid-
ing reaction, but simply runs forward. The direction of movement is in
this case determined by the part stimulated. These results have been
found to hold also in many other infusoria.

Experiments of the kind just described have shown that the anterior
end is as a rule much more sensitive than the remainder of the body
surface. A light touch, having no effect at the posterior end, produces
a strong reaction when applied to the anterior end.

It isa general rule that unlocalized mechanical stimuli, anh as are
produced by jarring the vessel containing the animals, have the same
effect as stimuli applied to the anterior end; they induce the Breitios
reaction.

In the positive contact reaction, the animal places itself in contact

118 BEHAVIOR OF THE LOWER ORGANISMS

with the solid object and remains against it. It may now continue quiet,
while the oral cilia bring a current of water containing food to the mouth.
But sometimes the animal
runs over the surface of the
solid, using its cilia as if they
were legs. This, as we have

Fic. 81. — Side view of Stylonychia creeping along seen, is the common method
a surface. After Piitter (1900). of locomotion in the Hypo-
tricha. A side view of one of the Hypotricha while creeping along a
surface is shown in Fig. 81. In-other cases the animal secretes a layer
or thread of mucus and thereby attaches
itself to the solid. Attached in this way
by a long thread (Fig. 82), Spirostomum
and Urocentrum often remain in a certain
position, revolving on the long axis. The
thread is usually quite invisible, but by
passing a needle between the solid object
and the animal, the latter may often be
pulled backward by the thread of mucus.
In still other cases the infusorian reacts
to solid objects by fixing its posterior end
firmly, remaining in this place for long
periods, like a plant. How this occurs in
Stentor is described in Chapter X.

The contact reaction is often directed
toward _ve ry_minute—objects, 2 ‘as_we haye

set forth in oerall.A in the case of Parame-
cium. It then serves the purpose of help-
ing to obtain food. In some of the fixed
infusoria such behavior is especially strik-
ing. \ Thus, if a small object touches gen-
tly one side ofthe disk of Stentor, .the-
animal may bend over toward it... This...
reaction may be seen when a_small.or-.
ganism in swimming about.comes. against
the disk of the animal, then attempts.to _=—-=— ===>
swim away. The Stentor. bends. in that. ,
direction, so as to keep in contact. with me ecatr eet at ones
e bottom by a thread of mucus
the organism as long as possible. At and remaining stationary with anterior
_ the same time, of course, the ciliary -vor- een
_ tex tends to draw the prey to the Stentor’s mouth,| This reaction
may be produced experimentally by attaching a bit of soft, flocculent

ANS ROO

FLL Y EO OWA

THE BEHAVIOR OF OTHER INFUSORIA 119

débris to the tip of a fine glass rod, and allowing this to touch the disk
of Stentor, then drawing it gently to one side. The Stentor follows it,
often bending far over (Fig. 83). The animal may thus bend in any
direction — to the right, to the left, or toward'oral or aboral side.

When infusoria are in contact with solids, their behavior always be-
comes much modified. The spiral movement of course ceases, and the
reaction to many stimuli — especially such reactions as depend largely
on the spiral movement — either cease or become changed. Animals
that when free place the axis of swimming in line with gravity, usually
take up, when in contact with solids,
any - position without reference to
gravity. To high temperatures at-
tached specimens respond much less
readily than do free swimming ones.
Stentor ceruleus responds readily to
light when free swimming, directing
its anterior end away from the
source of light; when attached, it
does not react in this way. Many
infusoria show a modified reaction
to the electric current when in con-
tact with solids. The flagellates
Chilomonas, ‘Trachelomonas, Poly- Br
toma, and Peridinium react readily to ree
the electric current when free swim- which is pulled by the experimenter to the
ming; not at all when in contact "8
(Piitter, 1900, p. 246). - Most ciliates when in contact with solids react
less readily to the electric current, and frequently when the reaction
does occur, it is of a different character from usual. While free speci-
mens place themselves in line with the current, attached infusoria often
take up a transverse or oblique position with the peristome or oral
side directed toward the cathode, — just as happens in Paramecium.
This is true in general for the Hypotricha.

What is the cause of the interference of the positive contact reaction
with the reaction to other stimuli? It is necessary, as we have seen in
our discussion of this reaction in Paramecium, to distinguish two factors
in the contact reaction; one physical, the other physiological. The
physical factor is found in the fact that the organism actually adheres
to the surface of the solid, —in many cases, at least, by means of a
mucous secretion. This physical adhesion would of course tend to pre-
vent that rapid movement under the influence of a stimulus which is
shown by free individuals. Thus, the animal might attempt to react

120 BEHAVIOR OF THE LOWER ORGANISMS

in the usual way, — showing the same ciliary movements as free indi-
viduals, — but might find itself stuck, and unable to escape. Doubtless
sometimes this condition of affairs is realized; it is described, for ex-
ample, by Piitter as present in the reaction of attached specimens of
Colpidium and some other infusoria. But in many cases this physical
factor will not account for the observed behavior. Infusoria in contact
may take different positions without difficulty, and could easily place
themselves in line with gravity, yet as a rule they do not doso. Attached
Stentors could easily bend into a position with anterior end away from
the light, yet their position shows no relation to the direction of the light
rays. There is nothing in the physical adherence to a surface that
should compel the animal to take a transverse position in the electric
current, rather than a position parallel to the current, yet this is what
occurs in attached specimens. It is clear that there is a physiological
factor involved. Contact with solids tends to make the animal act in
one way, the other stimulus in another; hence the two must interfere.
If we object, as some authors have done, to the admission that the contact
reaction interferes with the reaction to other stimuli, we are compelled
to admit in any case that the reactions to other stimuli do interfere with
the contact reaction, and one admission has as much theoretical signifi-
cance as the other. It is evident that when two agents influencing
the organism in opposite ways act simultaneously, the effect of one must
give way to that of the other, or the two must combine to produce a
resultant. It is impossible that each should produce its characteristic
effect. The interference of the contact reaction with the reactions to
other stimuli is one of the most striking phenomena to be observed in
the behavior of these lower organisms. It is always necessary to dis-
tinguish carefully the behavior of free swimming specimens from those
that are in contact with surfaces, for the two differ radically.

3- REACTION TO CHEMICALS

The reactions to chemical stimuli take place in all accurately known
cases through the typical avoiding reaction. As a rule the motor organs
of the infusoria, both flagellates and ciliates, act in such a way that a
current of water passes from in front of the animal to the anterior end
‘and mouth, as illustrated for Paramecium in Fig. 35. Thus when a
chemical is dissolved in the water, a “sample” of it is brought to the
most sensitive part of the body. If the chemical is of such a nature as
to act as a stimulus, the animal swims more slowly, stops, or moves
backward, turns toward the customary side (usually the aboral side),
until it no longer receives the chemical, then moves forward in the new

THE BEHAVIOR OF OTHER INFUSORIA 121

direction. Thus the region containing the chemical is avoided. In
many cases this reaction takes place in a very pronounced manner;
the animal shoots far backward, whirls rapidly toward the one side,
and repeats the reaction many times. In other cases the reaction is
less pronounced, and motion merely becomes a little slower as long as
the chemical is received in the ciliary current, while at the same time
the animal quietly.swings its anterior end about in a circle (as in Fig.
37 or 38). This continues until it finds a direction from which no more
of the chemical is received; in that direction it swims forward. If the
movements of the animal are not precisely observed, the method by
which the reaction occurs may in such cases be easily misunderstood.
There are various chemicals in which certain infusoria gather, pro-
ducing collections like those formed by Paramecium in acids (Fig. 43).
In all cases in which the facts are accurately known, these collections
are formed in the same way as are those of Paramecia. The animals
enter without reaction into the region where the substance is present, then
respond by the avoiding reaction whenever they come to the outer boun-
dary of the area containing the substance. Thus every individual that
enters the area of the chemical remains, and in the course of a longer
or shorter period a collection is formed here. In many cases this indirect
method of gathering together is strikingly evident, and the individuals
may be clearly seen to move about within the area containing the chemi-
cal, in the manner represented in Fig. 44. If the infusoria observed
are very minute, so that differentiations of the body are to be seen only
with great difficulty, if their movements are rapid, and if in the avoid-
ing reaction they do not swim backward, but merely stop and turn
toward one (structurally defined) side, at the same time revolving on
the long axis, then the reaction method is not so evident on a cursory
examination. In such cases, if the relation of the direction of turning
to the structural differentiations of the body and to the revolution on the
long axis are not carefully determined, the animal will be supposed to
turn directly, without variations of any sort, into the chemical. This
was formerly supposed to be the universal method of reaction to chemi-
cals. The cause for the turning was supposed to be found in the dif-
ference in the concentration of the chemical on the two sides of the
organism. The animal turned directly toward the side of greater con-
centration (“positive chemotaxis”) or of less concentration (“negative
chemotaxis”). This method of reacting to chemicals is no longer sup-
posed to exist for infusoria by any one familiar with the reaction method
described in the foregoing pages, so far as I am aware, save in the case
of certain very minute organisms, — fern spermatozoids, Saprolegnia
swarm spores, and the flagellate Trepomonas agilis (Rothert, 1901,

122 BEHAVIOR OF THE LOWER ORGANISMS

p- 388). But it is notable that in none of these cases has the relation
of the direction of turning to the differentiations of the body been ob-
served, and this is the crucial point for determining the nature of the
reactions. The fact that it is only for these very difficult objects that
the direct turning is maintained must make us cautious in accepting
this exceptional result.’

Let us now leave the method of reacting, and turn to certain more
general phenomena. In what chemicals do infusoria gather? What
chemicals do they avoid ?

In no other infusoria is the behavior toward different chemicals so
well known as in Paramecium. Chilomonas collects in acids in gen-
eral, and especially in solutions of carbon dioxide, just as Paramecium
does. Spontaneous gatherings are often formed by Chilomonas, and it
seems probable that these are due, as in Paramecium, to the carbon
dioxide produced by the animals themselves (Jennings and Moore,
1902). Cyclidium glaucoma and Colpidium colpoda likewise collect in
carbonic and other acids. Opalina, Nyctotherus, and Balantidium en-
tozoén, living in an alkaline medium, gather in acids, but if transferred
to an acid medium, they gather in alkali (Dale, 1901). Many other in-
fusoria show no tendency to gather in acids. Loxocephalus granulosus
and Oxytricha eruginosa form spontaneous collections resembling pre-
cisely those of Paramecium, but they are not due to the same cause.
These species do not collect in solutions of carbon dioxide, nor in other
acids. When they are mingled with Paramecia in the same prepara-
tion, they collect in one region, while the Paramecia collect in another.
It is apparent that Loxocephalus and Oxytricha produce some substance
to which the collections are due, and that this substance is not carbon
dioxide. A number of other infusoria form spontaneous collections,
the cause of which has not been investigated. Many of the commonest
species do not form such collections.

There are many chemicals in which one or another species of infusoria
have been found to collect. Most of the details are of comparatively
little general interest from the standpoint of animal behavior, so that we
shall not take them up here. An excellent summary of these results will
be found in Davenport’s “ Experimental Morphology” (Vol. I, pp. 32-45).
Certain general features are important for our purposes; these we may
bring out briefly.

First, from the way the collections are brought about, it is evident
that whether given infusoria tend to collect in a certain solution or not
depends on the nature of the solution in which they are already found.
This has been illustrated in detail for Paramecium. Paramecia in

' For a discussion of related points, see Chapter XIV.

THE BEHAVIOR OF OTHER INFUSORIA (123

strong salt solution collect in weak salt solutions or in tap water;
Paramecia in tap water collect in distilled water; Paramecia in dis-
tilled water collect in weak acids. In the same way, if two solu-
tions are open to any given infusorian, they tend to collect in that
one by which they are least repelled. Thus “attraction,” as deter-
mined by the formation of collections, is a relative matter; the infusoria,
like higher organisms, often have to put up with merely that by which
they are least repelled. To say that a certain infusorian gathers in a
given substance A, therefore, signifies little more than that it is less re-
pelled by this substance A, than by the substance in which it was found
at the time the experiment was tried.

Most flagellates and ciliates are repelled by strong solutions of chem-
icals of almost all sorts. This is true even for strong solutions of the
same substances in which they collect when the solutions are weak. In
such substances we can therefore distinguish an optimum concentration.
Below the optimum the organisms are indifferent, while above the opti-
mum they are repelled. Expressing the facts more concretely, at the
indifferent concentration no reaction is caused when the organism passes
into the solution or out of it; at the optimum concentration no reaction
is caused when the organism passes into the solution, but the avoiding
reaction is induced on passing out, while at concentrations above the
optimum the organisms react at passing inward. The result is then in
every case that they tend to gather in the optimum.

The reaction is in each case caused by a change from one concentra-
tion to another. The amount of change necessary to cause the reaction
has been shown, in the case of fern spermatozoids (Pfeffer, 1884), to bear
a definite relation to the concentration of the solution in which the organ-
isms are immersed. In other words, the amount of change necessary
to cause the reaction varies according to Weber’s law. Thus in the fern
spermatozoids the concentration of malic acid necessary to produce a
collection of the organisms must be about thirty times that in which the
organisms are already immersed.

Massart (1891) found that specimens of Polytoma uvella in his cultures
were not repelled by chemicals even in the strongest solutions. Such
cases are very exceptional; other investigators have found that even this
same organism (from other cultures) is repelled by various chemicals
(Pfeffer, 1904, p. 808, note).

The variability and inconstancy of the reactions of infusoria to
chemicals deserves emphasis. Whether infusoria of a given species
react to a certain chemical or not, and how they react, depends upon
the past and present conditions of existence of the individuals. The
general outlines of the reactions can be determined for any species, but

124 BEHAVIOR OF THE LOWER ORGANISMS

the details, especially from a quantitative standpoint, vary in accordance
with the environmental influences acting upon the individuals in question.

As a rule, infusoria collect in solutions of substances which may
serve them as food. This is almost invariably true for substances which
form the usual food of the organism under natural conditions. When
the amount of oxygen present in the water is low, most infusoria collect
about bubbles of air or other sources of oxygen.

Infusoria sometimes gather in substances which do not serve for
food or respiration, but which serve other important purposes in the
physiology of the species concerned. Thus, the flagellate spermato-
zoids of ferns were found by Pfeffer to gather in solutions of malic acid.
This substance is found in the fern prothalli, and probably occurs in
the mouth of the archegonium, into which the spermatozoids must enter
in order that fertilization may take place. The tendency to collect in
malic acid then doubtless plays a part in bringing about fertilization in
ferns. The collection of Paramecia in carbon dioxide seems to be an-
other case of a reaction which is useful to the organisms, though the
substance causing it does not itself serve as food.

Many infusoria collect, under certain circumstances, in substances
which do not serve as food and are not known to play any useful part
in the biology of the animal. Thus, Pfeffer found that the flagellate
Bodo saltans gathers in most of the salts of potassium, as well as in various
salts of lithium, sodium, rubidium, cesium, ammonium, calcium, stron-
tium, barium, and magnesium. This signifies only, as we have already
seen, that they are less repelled by solutions of these substances than
by the fluid in which they are situated. In most cases, as soon as
a substance is sufficiently concentrated to be injurious it becomes
repellent.

Whether the repellent effect of chemicals is due to the chemical
properties of the solution, or to its osmotic pressure, has been rigidly
determined only for Paramecium. In this animal, as we have seen, the
osmotic pressure is usually not the cause of the reaction. There is much
evidence that this is true for most species, but accurate quantitative
evidence is needed on this point.

4. REACTION TO HEAT AND COLD

Infusoria in general react to heat and cold in much the same way as
does Paramecium, — through the avoiding reaction. The way the reac-
tion occurs is most easily seen in the Hypotricha. The phenomena to
be observed are of special interest, because they show clearly how a
movement of a large number of individuals in a certain uniform direc-

THE BEHAVIOR OF OTHER INFUSORIA 125.

tion (“orientation”) may be brought about by the selection of varied

movements.

The common hypotrichan Oxytricha fallax, abundant in vegetable
infusions, is well fitted for the study of this reaction. A large number of
specimens are placed on a slide or trough. When one end of the trough

is gradually heated
by passing water at
a temperature of
40 degrees beneath
it, the Oxytrichas
at this end are
seen to become
very active, dart-
ing about in all di-
rections (Fig. 84).
Asthe temperature
rises, they give the
avoiding reaction,
—darting back-
ward, and turning
to the right. This
is alternated with
rapid dashes for-
ward. Whenever
a specimen passes
toward the warmer
end of the trough,
or when it comes
in contact with the
sides or end, it re-
sponds with the
avoiding reaction.
But a specimen
passing away from
the heated region,
in the direction of
the arrow at 14
(Fig. 84), does not
give the reaction,
because it is pass-
ing from a hot to
a cool region. The

Fic. 84. — Reaction of Oxytricha to heat. The slide is heated at
the end x. An Oxytricha in position 1 reacts as indicated by the arrows,
repeatedly moving backward, turning to the right, and moving forward,
thus occupying successively the positions 1-14. When it finally be-
comes directed away from the heat, as at 13-14, it ceases to change its
direction of movement, but continues to move straight ahead, thus
reaching a cooler region.

126 BEHAVIOR OF THE LOWER ORGANISMS

result is that all the specimens which swim in any direction but that
toward the cooler water are quickly stopped and turned, while all that
pass toward the cooler water continue in that direction. Since all the
specimens in the heated region are moving very rapidly and turning at
very brief intervals, in a short time all will have become directed
toward the cool water. Hence soon after the water has been heated at
one end of the trough, a stream of Oxytrichas will be seen passing

toward the cool water. The

animals are all “oriented” in

—_———
GSS a common direction, but the
is, orientation has taken place by
Gy, exclusion — through the fact
’ that movement in any other
‘ direction is at once stopped.
If one end is cooled to 10
degrees C. or below, while
‘4 the other is left at the usual
7 temperature, the Oxytrichas
: react in this same way in the
S)- cold region; hence they leave
it, as they before left the heated
—_ region. The reaction in the

Fic. 85. — Bursaria swimming backward ina case of cold is much less strik-

circle when heated. Ventral view. A

ing and less complete than. that
produced by heat. This is because the cold has the effect not only
of producing the avoiding reaction, but also that of making the move-
ments slower, and of finally benumbing the animals, so that they cease
to move. Thus it takes much longer for the animals to pass out of a
cold region than out of a warm region, and many of them do not suc-
ceed in escaping before the cold has stopped their movements.

The reaction of Oxytricha is essentially similar to that of Parame-
cium. But in Oxytricha the method of reaction is much more evident,
because the movements are slower, and there is usually no revolution on
the long: axis.

In many other infusoria the reaction to heat and cold has been
shown to take place in the same manner as in Oxytricha. In some
species the individuals show this type of behavior, yet with slight modifi-
cations that are such as to make the reaction quite ineffective, so that
the animals do not»escape from the heated region, and are finally killed.
‘This may be observed in Bursaria truncatella. If one end of a trough
containing specimens of Bursaria is heated, the animals respond with
the avoiding reaction, as Oxytricha does. They begin to swim back-

td

THE BEHAVIOR OF OTHER INFUSORIA 127

ward, and at the same time to circle to the right (Fig. 85). But they do
not alternate this with movement forward, as Paramecium and Oxytricha
do, and they do not revolve on the long axis. Bursaria simply continues
the reaction once begun, and this of course has little tendency to remove
the organisms from the heated region. ‘They circle about till they die.
Among different infusoria all gradations may be found, from the inef-
fective reaction of Bursaria through the moderately rapid but effective
behavior of Oxytricha to the quick movements of Paramecium, which
can be followed only with much difficulty.

Mendelssohn (1902) has determined the optimum temperature for a
considerable number of infusoria. He finds the following values: Para-
mecium aurelia, 24-28 degrees; P. bursaria, 23-25; Pleuronema, 25-27;
Colpoda, 25-31; Spirostomum’ teres, 24-33; Coleps, 28-31; Stentor,
25-28; Chlorogonium, 23-30. As a rule the organism is stimulated by
temperatures both above and below the optimum, so that it seeks the
optimum region. But in rare cases a higher temperature acts as a
stimulus, while a lower temperature does not. This is true, according
to Mendelssohn, in Pleuronema.

If the entire vessel containing the infusoria is heated, or if the ani-
mals are dropped into heated water, the avoiding reaction is produced,
just as when the heat is applied from one side. The animals swim back-
ward and turn to one side. It is thus evident that there need not be dif-
ferences of temperature in different parts of the body in order to produce
the avoiding reaction. In the experiment just mentioned the animal
“tries”? swimming in many different directions, but of course does not
find a direction that takes it away from the heated region.

LITERATURE VII
BEHAVIOR OF INFUSORIA IN GENERAL

A. Actionsystems, methods of movement and reaction: JENNINGS, 1900, 1899 4,
1902; PUTTER, 1904; NAEGELI, 1860; ROTHERT, 1901.

B. Reactions to contact with solids: PUTTER, Igoo.

C. Reactions to chemicals: PFEFFER, 1884, 1888; MASSART, 1889, 1891;
ROTHERT, 1901, 1903; GARREY, 1900; DALE, 1901; GREELEY, 1904; JENNINGS,
1900 a, 1900 6; JENNINGS AND MOORE, 1902.

D. Reactions to heat and cold: JENNINGS, 1904; MENDELSSOHN, 1902, 1902 4,

1902 6.

CHAPTER VIII
REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY

1. REACTIONS TO LIGHT

Like Paramecium, most colorless infusoria do not react at all to
light of ordinary intensity. But many species of infusoria are colored,
and these commonly react in a decided manner even to the light supplied
by the natural conditions of existence. Some react positively; they
gather in lighted regions or swim toward the source of light. Others
are negative, avoiding light regions and swimming away from the source
of light. We shall take up as examples the behavior of a negative or-
ganism, Stentor ceruleus, and of a positive organism, Euglena viridis.

A. Negative Reaction to Light: Stentor ceruleus

The blue Stentor is a trumpet-shaped organism, with a circle of large
adoral cilia or membranellez surrounding the large end or peristome.
This circle leads to the mouth, lying at one side of the disklike peristome.
The remainder of the body is covered with finer cilia.*_ The animal is
colored a deep blue. Stentor is often attached to solid objects by its
pointed end or foot, but it is likewise found at times swimming freely.

We shall have occasion to study the general features of the behavior
of Stentor, particularly when attached, in a later section (Chapter X).
Here we need to recall only the facts that in response to strong stimula-
tion it may contract, becoming shorter and thicker, and that when free
swimming it has an avoiding reaction similar to that of Paramecium.
When stimulated, it stops or swims backward, turns toward the right
aboral side, and continues forward in the new direction (Fig. 76). This
is the reaction produced by mechanical stimulation, by heat, and by
chemical stimulation acting either on the anterior end or on the body as
a whole. The results of localized stimulation have shown clearly that
the anterior end or peristome is more sensitive than the remainder of
the body surface.

1 For a figure of another species of Stentor, resembling in essentials the present one,
see Fig. 31, b.
128

REACTIONS OF INFUSORIA TO LIGHT. AND TO GRAVITY 129

The blue Stentor tends to gather in shaded regions, and when ‘sub-
jected to light coming from one side it moves away from the source of
light. Thus, if a glass vessel containing Stentors is placed near a win-
dow, the animals swim away from the source of light, and are soon found
to be collected on the side opposite the window.

How is this result brought about? Just what is the cause of the
reaction to light, and what is the behavior of the Stentors in reaching
the shaded regions?

In arranging experiments which shall answer these questions, let us
first try the effects of sudden strong changes in the intensity of the light
affecting the animals. This may be done
by placing a flat-bottomed glass vessel con-
taining many Stentors in a shallow layer of
water on the stage of the microscope in a
dark room. From beneath, strong light is
sent directly upward through the opening
of the diaphragm by means of the substage
mirror, while all other light is completely
excluded. In this way a circular area in
the middle of the field is strongly illumi-
nated, while the remainder of the vessel
containing the Stentors is in darkness.’

The Stentors in the darkness swim io. 86:65 Resi eee
about in all directions, but as soon as one at passing from a dark to a light
comes to the lighted area it at once re- ‘sion (1-4).
sponds by the avoiding reaction — it swims backward and turns toward
the right aboral side (Fig. 86, 1-4). Thus its course is changed and
it does not enter the lighted area. Since every Stentor reacts in this
way, the lighted area? remains empty. Usually the avoiding reaction
occurs as soon as the anterior end of the Stentor has reached the
lighted region. In other cases the entire Stentor passes completely into
the lighted area, then reacts in the usual manner, thus passing back
into the dark.

1 By using a projection lantern as the source of light the field of the microscope is
projected on the ceiling, or, by the use of a mirror to reflect the light at right angles, on
the ordinary projection screen. When thus projected, the behavior of the Stentors is
observable with the greatest ease.

? The light is passed first through a thick layer of ice water, in order to remove the
heat as far as possible. The fact that the reactions are not due to heat is shown in the
following manner. Specimens of Paramecium, an organism which is more sensitive to
heat than Stentor, but is not sensitive to light, are mingled with the Stentors. The Para-
mecia pass into the lighted region without hesitation, showing that this region is not
heated sufficiently to affect them; the heat then cannot affect the Stentors.

K

130 BEHAVIOR OF THE LOWER ORGANISMS

Thus an area lighted from below acts in the same manner as a region
containing a strong chemical. The animals keep out of both by the
avoiding reaction.

We may now arrange the conditions so that the light shall come from
one side, while at the same time differences in illumination shall exist in
different regions. This may
be done by placing the glass
vessel containing the Sten-
tors near a source of light
which falls obliquely from
one side, then shading a
portion of the vessel with a
screen. We may first so
place the screen that the
vessel is divided into right
and left halves, at equal
distances from the source of
light, but one shaded, the
other illuminated (Fig. 87).
4 The Stentors are at the be-

ginning scattered through-
out the dish and are

moving in all directions.
l \ — Stentors in the illuminated
half whose path lies in the

8 proper direction pass into

Fic. 87.— Reaction to light in Stentor. The light the shaded region without
comes from the left, as indicated by the arrows. S-Sisa y ion. Since nearly all
screen shading one half the vessel, so that the line x—y is eact Rate 5 “3 \
the boundary of the shadow. At 0, 1-4, is shown the keep in motion for a long
reaction of a Stentor on reaching this boundary line. 4; fter n interval
(The dotted outline a, 1-4, shows the reaction that would lime, ite t z
occur if the light caused increased activity in the cilia of nearly all will have passed

the side which it strikes.) into the shaded half.
Stentors in the shaded half respond by the avoiding reaction as soon
as they come to the boundary of the lighted area. That is, they
swim backward and turn toward the right aboral side (Fig. 87, 6). Thus
they remain within the shaded area, and after a short time most of the
Stentors in the vessel are to be found in the shaded half.
It is evident that the Stentors do not simply turn and swim parallel
with the light rays from the source of light. If this were the method
_ of reaction, a Stentor coming to the boundary x-y, Fig. 87, would turn
and swim directly toward the side y. This it does not do. The direc-
tion of turning depends upon the position of the right aboral side; the

bated Poe

REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 131

animal may even turn toward the source of light. The essential point
is the swimming back into the shaded region, without reference to the
direction from which the light comes.

Similar phenomena are observed if the side of the vessel next to the
source of light is shaded, the shadow of the screen reaching to the middle

s x
a.i
——§!
ee | B
!
tp
i 3
fed
fe |
s A 7) B

Fic. 88. — Reaction of Stentor to light when one half the vessel next the source of light is
shaded by a screen S-S (as indicated in Fig. 89). On reaching the line x—y, where it would pass
into the light, the animal responds as shown at ¢, 1-5.

of the vessel, so that the side farthest from the source of light is illumi-
nated (Figs. 88 and 89). Under such circumstances the Stentors gather
in the shaded area, next to the window. A specimen in the shaded area
which swims toward the lighted side is of course moving when it comes
to the boundary line in the same direction
as the rays of light. It nevertheless re-

sponds by the avoiding reaction, — stop-
ping, turning toward the right aboral side,
and swimming back to the
shadow. This often happens
when the animal has com-
S$ x

pletely passed the boundary

Fic. 89.— Side view of the conditions in the and is entirely within the
experiment shown in Fig. 88. The arrows show the lighted area (Fig. 88, 6). In
rere ot Nght. passing back into the dark-
ened area it now swims of course directly toward the source of light.

All together, then, our experiments thus far have shown that the cause
of the avoiding reaction is the change from darkness to light. At every
such change, Stentor responds by the avoiding reaction; that is, it tries
swimming in other directions until it is no longer subjected to the light.

Let us now arrange the conditions in such a way that all parts of the

"E320 - BEHAVIOR OF THE LOWER ORGANISMS

svessel are equally illuminated and the light comes from one side. This
amay be done by placing the Stentors in a glass vessel with plane sides, at
one side of the source of light, as a window or an electric lamp. Move-
ment from one part of the vessel to another cannot cause a change from
darkness to light, for all parts are equally lighted.‘ Yet the Stentors

Li

Fic. 90. — Method of observing the reaction of Stentor to light. A and B are two electric
lights, which can be extinguished or illuminated separately.

usually, after a short interval, turn and swim away from the source of
light, after a time reaching that side of the vessel farthest from the lamp
or window. If the animals are observed as they turn, it is found that
the turning is brought about through the avoiding reaction. A short
time after the light is directed upon them, they swim more slowly or
cease the forward movement, and begin to swerve more strongly toward
the right aboral side, thus swinging the anterior end about in a circle.
The direction of movement thus becomes changed; in the new direc-
tion the animal swims forward. If its anterior end is still not directed
away from the source of light, the avoiding reaction is repeated; the
animal continues to try new directions till the anterior end is directed
away from the lighted side. In that direction it continues to move, so
that it finally comes to the side opposite the window or lamp.’

1 There is of course an infinitesimal difference in the illumination of different parts
of the vessel, due to the fact that one part is nearer the source of light than another.
The experiment succeeds equally well when the sun is employed as the source of light,
in which case the difference of illumination in different regions is practically infinitely
minute. The reaction cannot be therefore conceived as due to these differences.
Experiments show that the differences in illumination necessary to produce reaction
are much greater than those obtaining in different parts of a vessel thus lighted from
one side.

2 The reaction may be obtained by focussing the Braus-Driiner binocular micro-
scope on a shallow vessel of Stentors swimming about at random in a diffuse light, then
allowing a strong light from an electric lamp or a brightly lighted window to fall upon

them from one side. In order to have the reaction repeated many times, so as to give

opportunity for careful study, the vessel containing the Stentors may be placed between
two electric lights, as in Fig. 90. One of these lights can be extinguished at the same
instant that the other is brought into action ; by repeating this process the direction of
the light rays is repeatedly reversed. At each reversal the Stentors react in the way
described in the text.

REACTIONS OF INFUSORIA TO LIGHT» AND TO GRAVITY °133

Why does the animal react in this way, even when the vessel is not
divided into regions of light and darkness, but is lighted from one side?
The essential problem is, Why does a specimen swimming transversely
or obliquely to the direction of the light rays give the avoiding reaction
and continue this until the anterior end is directed away from the
source of light ?

To understand this, certain facts need to be recalled. We know
that the anterior end is much more sensitive than the remainder of the
body. We know that an increase in illumination causes the avoiding
reaction. We know that this is true even when the anterior end alone is
subjected to such a change. Now, Stentor swims in a spiral of some
width, so that its anterior end swings always in a circle, and is pointed
successively in many different directions. If the animal is swimming ~
transversely or obliquely to the direction of the light rays, the anterior -
‘end in one phase of the spiral path is directed more nearly toward the
source of light, in another phase more nearly away from it, so as to be
partly shaded, — as is illustrated for Euglena in Fig. 94. ‘The result is,
of course, that the sensitive anterior end is subjected to repeated changes
in intensity of illumination; at one instant it is shaded, at the next the
light shines directly upon it. As we know from other experiments, the
change from light to darkness produces no reaction, while the changes
from darkness to light produce the avoiding reaction. Every time,
therefore, that the anterior end swings into the light, the avoiding reac-
tion is caused; the animal therefore swings its anterior end in a large
circle, trying many directions. Every time it swings its anterior end
away from the source of light into the shadow of its body, on the other
hand, no reaction is produced; the position thus reached is therefore
retained. This process continues, the animal trying new directions
every time its anterior end swings toward the light, until in a short time
the anterior end must inevitably become directed away from the light.
In this position the anterior end is no longer subjected to changes in
illumination, for the axis of the course coincides with the axis of the light
rays, and the body maintains a constant angle with the axis of the course.
The amount of light received by the anterior end therefore remains con-
stant. Hence there is no further cause for reaction, and the organism
retains the position with anterior end directed away from the source of
light.

Attached specimens of Stentor do not become oriented with refer-
ence to the light. ‘They may occupy any position with reference to the
direction from which the light comes, even though the light shines di-
rectly on the anterior end. We have seen previously that contact inter-
feres with many of the reactions of organisms. But if the animals are

134 BEHAVIOR OF THE LOWER ORGANISMS

subjected to a sudden, powerful increase in the intensity of the light
falling upon them, they often contract (Mast, 1906), and later bend in
various directions, till they have become accustomed to the light.

To sum up, the orientation of the free Stentor in line with the light
rays, with its anterior end directed away from the source of light, is due
to the fact that an increase of illumination at the sensitive anterior end
induces the avoiding reaction. As a necessary result the oriented
Stentor swimming in a spiral path tries new directions of movement until
it finds one where such changes of illumination no longer occur. Such
a direction is found only in orientation with the anterior end directed
away from the source of light. From a knowledge of the spiral course
and the fact that increase of illumination at the anterior end causes
_ the avoiding reaction, this result could be predicted. The reaction to
light, like that to most other stimuli, is based on the method of trial of
differently directed movements, till one puts an end to the stimulation.

B. Positive Reaction to Light: Euglena viridis

Euglena is not closely related to Stentor; it is a flagellate, while
Stentor is a ciliate. If we find similar principles governing the reaction
to light in these widely separated organisms, it is probable that these
principles are valid for the infusoria in general.

Euglena viridis (Fig. 74) is a fish-shaped green organism, often
found abundantly in the water of stagnant roadside pools, giving them
a green color. -At the anterior end is a notch from which there extends
a single long flagellum, by the lashing of which Euglena swims. Within
the body are chlorophyll masses, giving the organism its green color.
Near the anterior end, close to the side bearing the larger lip of the
notch, — the “dorsal” side, — is a red pigment spot, usually known as
the eye spot. As we have seen previously, the “‘action system” of
Euglena resembles in essentials that of Paramecium. It swims in a
spiral (Fig. 94), and to most stimuli it responds by an avoiding reaction
which consists in stopping or backing, then turning more strongly than
usual toward the ‘‘dorsal”’ side.

If the light is not too strong, Euglene gather in lighted areas, and
when the light comes from one side, they swim toward the source of
light. Thus in the culture jar the organisms are usually found on the
side next the window or other source of light. In very powerful light,
such as the direct rays of the sun, however, Euglena swims away from

the source of light. How is this behavior brought about ?

Let us first study the effect of changes in the intensity of the light.
The Euglenz are placed on a slide in a thin layer of water, and are ex-

REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 135

amined with the microscope in the neighborhood of a window.
all the Euglene are seen swimming toward the window.

Fic. 91.— Diagram of the reaction of Euglena when the
light is decreased. ‘The organism is swimming forward at 1;

when it reaches 2 it is shaded. It thereupon swerves toward
the dorsal side, at the same time continuing to revolve on the
long axis, so that its anterior end describes a circle, the Eu-
glena occupying successively the positions 2-6. From any of
these it may start forward in the directions indicated by the
arrows.

light is decreased by placing the hand or a
screen between them and the window. At once
all give the avoiding reaction; that is, they stop
or swim backward an instant, then swerve
strongly toward the dorsal side, so that the ante-
rior end swings about a circle (Fig. 91). If the
light is decreased strongly, the anterior end de-
scribes a wide circle or may even turn through
an angle of 180 degrees, so that the direction
of movement is reversed. If only a little of the
light is cut off, the anterior end describes only a
narrow circle. The organisms soon resume the
forward movement, but now the axis of the
spiral path coincides with one of the directions
indicated by the anterior end in swinging about

Soon

Now the

/

Fic. 92. — Change of
direction in the spiral path
of the Euglena, as a result
of a slightly marked reac-
tion. Ata the illumination
is decreased, causing the
organism to swerve toward
the dorsal side, thus widen-
ing the spiral path. At b
the ordinary swimming in a
narrow spiral is resumed;
since at this point the organ-
ism was necessarily more
inclined to the axis of the
spiral than before the reac-
tion, the new course lies at
an angle to the previous one.

136 **\ >! BEHAVIOR OF THE LOWER ORGANISMS

a circle.’ In other words, the direction of the path has been changed
(Fig! 92). ‘The whole action may be expressed as follows: when the
light is suddenly decreased, the organism tries successively many
different directions, finally following one of these.

The reaction is a very sharp and striking one, and produces a most
peculiar impression. At first all the Euglenz are swimming in parallel
lines toward the window. As soon as the shadow of the hand falls upon
the preparation, the regularity is destroyed; every Euglena turns strongly
and may appear to oscillate from side to side. This apparent oscilla-
tion is due to the swerving toward the dorsal side, combined with the
revolution on the long axis. The organism swings thus first to the
right, then upward, then to the left, then down, etc. (see Fig. gr).

This reaction occurs whenever the light is decreased in any way.
Thus, in place of cutting off the light coming from the window, that
coming from the mirror of the microscope may be decreased by closing
‘the iris diaphragm. The Euglene react in the manner above de-
scribed, though they soon resume their movements toward the window.
Again, if the light from the window is decreased only slightly, the Eu-
glenz react in the manner described, thus changing their direction of
movement; very soon, however, they swim again toward the window.
The same reaction occurs in Euglene that are for any reason not swim-
ming toward the source of light. Even if a specimen is swimming away
from the window, it gives the avoiding reaction in the usual way when
the light from the window is decreased.

It is clear that the reaction is due to the decrease in the intensity of
light, not to a change in the direction of the light rays. In the first and
second experiments mentioned in the preceding paragraph, the Euglenz
are, some time after the light is decreased, swimming in the same direc-
tion as they were before, though at the moment of decrease there is a
reaction.

Engelmann (1882) tried shading parts of the body of Euglena. He
found that a shadow which is cast on the body of the organism without
affecting the anterior one-third produces no effect whatever. On the
other hand, a shadow affecting only the anterior tip —if even only the
part in front of the eye spot — causes the same reaction as shading the
entire body. Thus it is clear that the anterior end is more sensitive to
light than the remainder of the body. These results of Engelmann are .
of much importance for understanding the remainder of the reaction to
light.

If Euglenz are placed on a slide and a certain spot is lighted from
below by the mirror of the microscope, a dense collection is in the course
of time formed in the lighted region. Observations show that the Eu-

REACTIONS OF INFUSORIA TO LIGHT AND: TO GRAVITY 137

glenz in the darker portion swim about at random; many of them thus
pass into the lighted region. There is no reaction at passing from the
dark to the light. In the lighted region they likewise swim about in all
‘directions. But as soon as an individual reaches the outer boundary of

See! a

1

Fic. 93.— Illustration of the devious path followed by Euglena in becoming oriented .
when the direction of the light is reversed. From x to 2 the light comes from above; at 2 it
is reversed. The amount of wandering (a—/) varies in different cases.

the lighted area, it gives the typical avoiding reaction; it backs, turns
toward the dorsal side, and thus reénters the lighted area. This reac-
tion frequently occurs as soon as the anterior tip is pushed into the shade.
In other cases the reaction does not occur till the Euglena has passed

138

BEHAVIOR OF THE LOWER ORGANISMS

completely into the dark; it then turns and passes back into the light.

’

/
/
‘
,
é
é / oe
¢
,
/
‘

c
a
\
b ee
! foe
a

Fic. 94.— Spiral path of Eu-
glena. a, b,c, d, successive positions
taken. The arrows at the right in-
dicate the direction of an incoming
force, as light, showing how the rela-
tion of the body axis and the anterior
end to such a force changes con-
tinually. At d the body axis is
nearly parallel to the lines of force,
and the anterior end is directly illu-
minated. At 6 the axis is nearly
transverse, and the sensitive anterior
end is largely shaded, so as to re-
ceive but little light.

At the boundary of the lighted area the
organism is, of course, subjected to a sud-
den decrease in illumination, and this, our
previous experiments have shown us, is the
cause of the avoiding reaction. Whenever
lighted or shaded areas are open to Eu-
glenz, the organisms gather in the lighted
areas in the way just described.

If the entire area containing the Eu-
glene is illuminated from one side, the
organisms swim toward the side from
which the light comes. That is, they be-
come oriented with anterior end toward
the source of light. If we watch them as
they become oriented, we find that the
orientation takes place, as in Stentor,
through the avoiding reaction. The course
of events is about as follows : The Eu-
glen are swimming about at random in
a diffuse light, when a stronger light is
allowed to fall upon them from one side.
Thereupon the forward movement _be-
comes slower and the Euglene begin to
swerve farther than usual toward the
dorsal side. Thus the spiral path be-
comes wider and the anterior end swings
about in a larger circle and is pointed
successively in many different directions.
In some part of its swinging in a circle
the anterior end of course becomes directed
more nearly toward the light; thereupon
the amount of swinging decreases, so that
the Euglena tends to retain a certain posi-
tion so reached. In other parts of the
swinging in a circle the anterior end be-
comes less exposed to the light; thereupon
the swaying increases, so that the organism
does not retain this position, but swings
to another. The result is that in its spiral
course it successively swerves strongly
toward the source of light, then slightly

REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 139

away from it, until by a continuation of this process the anterior end is
directed toward the light. In this position it swims forward. The
course of Euglena in becoming oriented is shown in Fig. 93.

This behavior is intelligible when we recall the effect of the spiral
course in causing changes in the intensity of the light affecting the an-
terior end. The anterior end is, as we have seen, the part most sensi-
tive to light; it may be compared with the eye of a higher animal. Ina

TTL

Fic. 95. — Diagram of the method by which Euglena becomes oriented with anterior end
toward the source of light. At 1 the organism is swimming toward the source of light. When
it reaches the position 2, the light is changed, so as to come from the direction indicated by
the arrows at the right. As a consequence of the decrease of illumination thus caused, the
organism swerves strongly toward the dorsal side, at the same time continuing to revolve on the
long axis. It thus occupies successively the positions 2-6. In passing from 3 to 6 the illumi-
nation of the anterior end is increased, hence the swerving nearly ceases. In the next phase
of the spiral therefore the organism swerves but a little, — from 7 to 8. But this movement
causes the anterior end to become partly shaded, and this decrease of illumination again in-
duces a strong swerving toward the dorsal side. Hence, in the next phase of the spiral the
organism swings far, through 9 and ro, to rz. Thus it continually swerves much toward the
source of light and a little away from it, till it reaches the position 16. Now it is directed
toward the source of light, and such swerving as occurs in the spiral course neither increases
nor decreases the illumination of the anterior end. Hence there is no further cause for re-
action; the Euglena continues its usual forward movement, which now takes it toward the
source of light.

Euglena swimming obliquely or transversely to the rays of light, as in
Fig. 94, the illumination of the anterior end changes greatly with each
turn in the spiral. At d the light is shining almost directly upon the
anterior end, while at 6 the organism is nearly tranverse, so that the
anterior end is partly shaded. The effect is like that of turning an eye
first toward the sun, then away from it; though the movement is slight,

140. _. BEHAVIOR OF THE LOWER.ORGANISMS

the change in illumination produced is great. The variations in
illumination due to the spiral course are doubtless much accentuated
by the fact that one side of the anterior end bears a pigment spot, which
in certain positions of the unoriented Euglena cuts off the light. A
decrease of illumination causes, as we know, the avoiding reaction;
the anterior end swings in a wider circle (Fig. gr). This still further
increases the variations in the illumination of the anterior end. Every
time the illumination is decreased, this causes the animal to swerve still
more; so that its anterior end becomes pointed in many different direc-
tions, till it comes into one where such changes in illumination no longer
occur. Such a position is found when the animal is swimming toward
the source of light. Now the axis of the body retains always the same
relation to the direction to the rays of light, so that the anterior end is
not subjected to variations in intensity of illumination. There is then
no further cause for reaction. Orientation is thus reached by trying
various directions. This will be best understood by an examination
of Fig. 95, together with its explanation.

Euglena responds most readily to light of a blue color (Engelmann,
1882). Passage from blue light to light of other colors has essentially
the same effect as passage from stronger to weaker light. If the differ-
ence between the two is sufficiently decided, Euglena responds by the
avoiding reaction in passing to the other color; it therefore remains in
the blue. If a small spectrum -is thrown on a slide containing many
Euglene, they gather in larger numbers in the blue, — especially in
the near vicinity of the Frauenhofer’s line F.

Very strong light, such as direct sunlight, has an effect on Euglena
precisely the opposite of that produced by weaker light. If the organ-
isms are subjected suddenly to sunlight, they give the avoiding reac-
tion. They tend therefore to gather in less lighted regions. If the
sunlight falls upon them from one side, they become oriented with an-
terior ends away from the source of light, and swim in that direction.
The orientation takes place in exactly the way described above, save
that now it is the increase of light at the anterior end that causes the
avoiding reaction. If a vessel is placed in such a position that the sun
shines on it from one side, while the half of the vessel away from the sun
is shaded with a board, the following result is produced: The Euglene
gather in a band at the edge of the shadow (Fig. 96). They do not
pass into the dark area beneath the shadow, nor do they remain in
the region affected by direct sunlight, but in an area of intermediate
illumination.’

? This experiment is due to Famintzin (1867, p. 21).

' REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 141

We can thus distinguish an optimum intensity of light, in which
Euglena tends to remain. Movement toward either a greater or a less
intensity of light causes the avoiding reaction, with its trial of different
positions and directions of movements,
till a position or direction is found
which leads toward the optimum, or
retains the optimum intensity undi-
minished. Or, in other words, after
Euglena receives an amount of light
which we might call “enough,” it
avoids more light, and also less light. ae
That degree of light in which it tends henge mines eae
to remain seems to be about the light comes from the direction indicated
amount which is most favorable to its by the arrows, while the opposite side of
; Di G re : the vessel is shaded, as indicated by the
life activities. Euglena requires light dots. The Euglene gather in the inter-
for assimilating carbon dioxide by the ™édiate region, across the middle.
aid of its chlorophyll, just as do higher plants. If confined to dark-
ness, it soon ceases activity, contracts into a sphere, and becomes en-
cysted. On the other hand, direct sunlight is very injurious to it; if
long continued it causes the organism to fall to the bottom and die.
Euglena avoids both the higher and the lowet,-4 intensities that are
injurious to it.

C. Negative and Positive Reactions compared

Thus in both negative organisms (Stentor) and positive organ-
isms (Euglena), the determining cause of the reaction is a change in
the intensity of light, and the reaction takes place by the usual method of
the performance of varied movements, subjecting the animal succes-
sively to different conditions. When the sensitive anterior end is sub-
jected alternately to light and shade, the organism “tries” other direc-
tions of movement till it finds one where such changes are not pro-
duced. In Stentor it is an increase in light that causes this reaction;
in Euglena is it usually a decrease that causes the reaction, though
when the light is very strong an increase may have the same effect.

D. Reactions to Light in Other Infusoria

The reactions of other infusoria to light are similar in character,
so far as known, to those of Stentor and Euglena. In only a few other
cases have details of the avoiding reaction been worked out as thoroughly
as for the two species mentioned. But all that we know of the reac-
tions of infusoria to light is consistent with the method of reaction known

142 BEHAVIOR OF THE LOWER ORGANISMS

to exist in Stentor and Euglena; indeed, the evidence seems clear that
these reactions take place in essentially the same way throughout the
group. In Cryptomonas ovata, and less completely in the swarm
spores of Chlamydomonas and Cutleria, the present writer has observed
that the reaction to light is of the same character as in Euglena. We
shall pass in review certain general features of the reaction in other
infusoria, as described by various authors.

As we have before noted, most colorless infusoria give no indication
of sensitiveness to light. But color is not absolutely necessary in order
that reaction to light may occur, as is shown by the fact that Amceba~
reacts to light. Even in the infusoria, colorless species may react to
light when such behavior is distinctly beneficial to the organism. A
species of Chytridium, a colorless flagellate that is parasitic on the
green organism Hzmatococcus, reacts to light in the same manner as
Hematococcus, collecting as a rule in lighted regions, or at the side of
the vessel next the source of light (Strasburger, 1878). This, of course,
aids it in finding its prey, which collects in the same regions. Several
other colorless infusoria that are parasitic on green flagellates have
been found to react to light in the same manner as their prey. Ver-
worn (1889, Nachschrift) found that the colorless ciliate Pleuronema
chrysalis reacts to a sudden increase in the intensity of light by a rapid
leaping movement, — evidently a strongly marked avoiding reaction.
Certain colorless infusoria react, as we shall see later, to ultra-violet
light.

In the green ciliate Paramecium bursaria the reaction to light de-
pends, according to Engelmann (1882), on the amount of oxygen in
the water. This animal contains chlorophyll, which produces oxygen
in the light. When there is little oxygen in the water, the organism
gathers in lighted regions, thus of course increasing its store of oxygen.
When the individuals in the light come to the boundary of a dark region,
“they turn around at once into the light, as if the darkness was unpleas-
ant to them” (/.c., p. 393). The response is thus clearly an avoiding
reaction, like that of Stentor. When the water contains much oxygen,
on the other hand, Paramecium bursaria avoids the light. On reach-
ing a lighted area the animals react in the way above characterized,
and return into the darkness. When they gather in light, it is especially
in the red rays of the spectrum that they collect; these are the rays in
which the chlorophyll is most active. When they avoid light, it is
again the red rays that are most effective in producing the avoiding
reaction.

Hertel (1904) found that Paramecium bursaria, Epistylis plicatilis,
Stentor polymorphus, and Carchesium react to ultra-violet light, of

REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 143

280 pp wave length. In the two species last named the chief reaction
observed was a sudden contraction. Epistylis bends to one side under
the action of the light, while Paramecium bursaria reacts in essentially
the same manner as to ordinary light, as described above. All died
quickly under the action of powerful ultra-violet light.

The flagellate swarm spores of many alge react to light. Their
behavior in this reaction has been studied especially by Strasburger
(1878). These swarm spores (Fig. 97) usually resemble Euglena in
essential features, though they may differ in form, in the number of
flagella, and in other details. They contain chlorophyll or other color-
ing matter, and usually a red eye
spot. The action system of the
spores is similar to that of Euglena.
They swim in a spiral path, keeping
a certain side always toward the axis
of the spiral (Naegeli, 1860, p. 96).

On coming to an obstacle, they react _ Fic. 97.— Examples of swarm spores,
by-t ° t ide (N ie after Schenck. «@, Hematococcus pluvialis;
y turning to one side ( aegel, C.), 6, Ulothrix zonata; c, Botrydium granulatum,

with or without a previous start gamete; d, Cladophora glomerata; ¢, Edo-
backward. It is probable that the °°"

turning in response to a stimulus is always toward the side directed
outward in the spiral path, as it is in Euglena, Chilomonas, and Cryp-
tomonas. The movements of the swarm spores, so far as known, exactly
resemble those of the organisms just named. It is further without
doubt true that the anterior end is in the swarm spores, as in other
infusoria, the most sensitive part of the body. The swarm spores are.
much smaller than Euglena, so that the details of the behavior are less
easy to determine.

Strasburger found that when the light is weak, all the colored swarm
spores * swim toward the lighted side of a drop (positive reaction).
When the light is strong, some swim away from the lighted side (nega-
tive reaction). If different parts of a drop or a vessel are unequally
illuminated, the swarm spores gather in the lighted region. The phe-
nomena are thus in general similar to those found in Euglena. There
are certain variations among the different swarm spores. ‘Thus, Stras-
burger found that Botrydium and Cryptomonas are positive even in the
strongest light, while in a weak light Cryptomonas is indifferent. But
in most species there is, as in Euglena, an optimum. In light below

’ Strasburger studied the swarm spores of Hamatococcus lacustris, Ulothrix, Cheto-
morpha, Ulva, Botrydium, Bryopsis, CEdogonium, Vaucheria, and Scytosiphon, as well
as the flagellate Cryptomonas (called Chilomonas by Strasburger), and the colorless
swarm spores of Chytridium and Saprolegnia.

144 |. | BEHAVIOR OF THE LOWER ORGANISMS

thé;optimum they are positive; in light above the optimum they are
negative. |

Strasburger did not determine the precise movements of the organ-
isms in the reaction to light. That is, he did not determine toward
which side they turn in becoming oriented. But in other respects his
account is so excellent that, with the fuller results on Euglena as a key,
it is not difficult to analyze out the precise factors in the behavior.

If the light affecting the organisms is suddenly decreased in intensity,
Strasburger found that the swarm spores (Botrydium and Ulva) sud-
denly turn toward one side (/.c., p. 25). In Bryopsis this reaction was
produced also when the light was suddenly increased. In all the swarm
spores it was evident that as soon as the light was decreased by the in-
terposition of a screen the path became more crooked (l.c., p. 27).
In other words, the spiral became wider, owing to the increased swerv-
ing toward a certain side. In these respects the swarm spores precisely
resemble Euglena. It is clear that they react to a sudden decrease in
illumination by an avoiding reaction, which consists in turning more
or less strongly toward a certain side, with or without a cessation of the
revolution on the long axis; in this way the direction of progress is
changed.

As would be expected from this method of response, the organisms
react at passing from a light to a dark region. If a ring is placed over
the drop containing the organisms, so that only a central circle is illu-
minated, the positive organisms gather in the illuminated circle (Fig.
98, A). Here they swim toward the window from which the light
comes, but on reaching the edge of the shadow, they turn back into the
lighted region (/.c., p. 28). Often the organism passes completely
into the shadow before reacting, then it turns and swims back into the
light. Thus it does not react till a short time after the moment of change.
If a narrow band of shadow passes across the middle of the drop, trans-
versely to the direction from which the light is coming, this usually does
not stop the organisms, because of this interval of time which elapses
before their reaction; before they begin to react they have passed com-
pletely across the band into the lighted region beyond. But if a larger
vessel is used and a broader transverse band of shadow passes across
it (Fig. 98, B), this does stop the organisms. They gather on the edge of
the shadow without passing across it. In many other ways Strasburger
shows that when the area containing the swarm spores is unequally
illuminated, the positive organisms collect in the more illumined region.
In this they precisely resemble Euglena, as Strasburger himself noted.
The behavior is of course a direct result of the production of the avoid-
ing reaction by a decrease in light.

REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 145

If the experiments were made with swarm spores that were nega-
tive to the intensity of light used, they gathered of course in the shadow
instead of in the light. If a board was placed across the middle of the
vessel from right to left, such swarm spores formed a collection in the
partly shaded region at the edge of the board (as in Fig. 96), where they
found the optimum degree of illumination. They were repelled both
by the strong light and by the deep shadow.

Thus it is clear that in the swarm spores, as in Euglena and Stentor,
a change in the intensity of illumination produces reaction. But a
certain amount of change is required before any effect is produced.
If the intensity of illumination changes only very gradually from one

Fic. 98. — Diagrams to illustrate the results of some of Strasburger’s experiments with
positive swarm spores (original). A, the margins of the drop are shaded (as indicated by the
dots); the organisms gather in the lighted centre. B, a broad band of shadow lies trans-
versely across the drop; the organisms swim toward the light, but are stopped by the shadow.
Thus two groups are formed, one at the side of the drop next the light, the other in a corre-
sponding position at the edge of the shadow.

region to another, the difference in intensity between succeeding points
is insufficient to cause reaction. Hence under these circumstances the
organisms remain scattered and move about without reaction. Stras-
burger showed this in the following way. He used a hollow wedge-
shaped prism, 20 cm. long, filled with a partly opaque solution of humic
acid in ammonia. Through this the light was passed. At the thin
end of the wedge nearly all the light was transmitted; at the thick end
little or none, and there was a gradual transition from light to dark
between the two ends. This prism was placed over the drop contain-
ing the swarm spores, and the light was allowed to fall directly from
above (Fig. 99, X). The drop being very small in comparison to the
length of the wedge-shaped prism, there was of course but little differ-
ence in the illumination of its two sides, and the transition from one
to the other was very gradual. Under these conditions the swarm
spores remained scattered throughout the drop. The change in pass-
L

146 BEHAVIOR OF THE LOWER ORGANISMS

ing from one region to another was not sufficiently marked to cause
reaction.’ .

When the entire area is equally lighted and the light comes from
one side, the positive swarm spores swim toward the source of light.
If the light is made strong, most species swim away from its source.
In this behavior the agreement with Euglena is complete. The orien-

Fic. 99. — Diagram of the conditions in Strasburger’s experiments with a wedge-shaped
prism, constructed from the data furnished by Strasburger. a, prism 20 cm. in length, filled
with a translucent fluid. 6, hanging drop containing the swarm spores. X, rays of light
coming from above, as in the first experiments. Y, rays coming obliquely from the thicker
end of the wedge, as in the second set of experiments. The figure is one half natural size.

tation takes place gradually, by a series of trials, as in Euglena. Stras-
burger paid no special attention to this point, but the present writer
has observed that this is true in Cryptomonas, Chlamydomonas, and
the swarm spores of the marine alga Cutleria, as well as in Euglena,
and Strasburger (1878, p. 24) notes incidentally that it is true in Hema-
tococcus.”

It seems clear, then, that the reaction takes place in the same manner

1 It is curious that Strasburger drew from this experiment the erroneous conclusion
that variations in the intensity to light play no part in the reaction. The only essential
difference between this experiment and the previous ones (Fig. 98) is that in the pre-
vious experiments the change of illumination in passing from one region to another
is sudden and pronounced, while in the present experiments it is slow and gradual.
The logical conclusion is that the lack of reaction in the present experiment is due to
the slightness of the change in passing from one part of the preparation to another.
When we consider that the prism was 20 cm. in length, and was placed over a mere
drop, it is evident that the difference in illumination in different parts of the drop
was excessively small. We know that for the effective action of all stimuli a certain
threshold amount of change is necessary, so that the results are exactly what might
be anticipated. Our account of Euglena shows beyond doubt that a change in intensity
of illumination does cause reaction. Strasburger himself (J.c., p. 25) observed the same
fact in swarm spores, though he paid little heed to this observation in the remainder of
the work.

? He says that when the direction of the light is changed, the swarm spores become
oriented “* Nach verschiedenen Schwankungen.”

REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 147

in the swarm spores asin Euglena. As set forth on page 139, the move-
ment toward or from the source of light, in a field of which all parts
are equally lighted, is due to the fact that in the unoriented individuals
the sensitive anterior end is subjected to frequent changes in the inten-
sity of illumination. It is first directly lighted, then shaded. These
changes induce reaction. By the method of trial the organism then
comes into a position such that these changes cease. Such a position
is found only in orientation. All these relations evidently hold equally
well for the swarm spores; for details the reader may refer to the ac-
count of the behavior of Euglena.

What happens if the field containing the organism is lighted from
one side, and there are at the same time variations in the intensity of
light in different parts of the field? Strasburger devised certain ex-
periments to answer this question. These experiments have become
celebrated, and an immense amount of ingenuity has been expended
in endeavoring to interpret them in one way or another. Strasburger’s
experiments involved the use of the wedge-shaped prism shown in
Fig. 99. This prism was placed over the drop containing the swarm
spores, in such a way that the light came obliquely from the direction
of the thick end of the wedge, as in Fig. 99, Y. Now the intensity of
illumination is greater on the side farthest away from the source of
light, and decreases as we pass toward the source of light. Will the
positive swarm spores move toward the source of light, and thus into a
region of less illumination, or will they rather move into the region of
greater illumination, and thus away from the source of light? .

Strasburger found that the positive swarm spores move toward the
source of light, and hence into the region of less illumination. It is
extraordinary that this result should have occasioned the surprise and
comment which have been bestowed upon it. Strasburger’s previous
experiment with perpendicular light (Fig. 99, X) had shown that the
variations in intensity of illumination in different parts of a drop under
this prism were too slight to cause reaction, the organisms remaining
scattered throughout the drop. Evidently so far as the organisms were
concerned these slight variations did not exist; they were not perceived.
Therefore, when the light comes from one side, the organisms react
exactly as they do when such variations do not exist. They swim
toward the source of light for the same reason that they do when the prism
is not present. The experiment consists essentially in making the differ-
ences in the intensity in neighboring regions so slight that they are un-
perceived. We need not, therefore, be surprised that the organisms fail
to react to them.

The experiments show, what they were designed to show, that the

-148 BEHAVIOR OF THE LOWER ORGANISMS

reason for swimming toward the source of light is not the progression
into a lighter region. But they do not indicate in the least that the
reactions are not due to changes in intensity of illumination. So long
as turning the sensitive anterior end away from the source of light
causes a greater decrease in its illumination than does movement into
the slightly less illuminated region, the organism will move toward the
source of light. If the difference in intensity of light in different parts
of the drop were increased till the change in illumination due to pro-
gression is greater than the change due to swinging the anterior end away
from the source of light, then the positive organisms would gather in
the more illuminated regions. This is the condition of affairs in the
experiment shown in Fig. 98.

In the swarm spores, as in Euglena, the positive reaction usually
changes to a negative one when the light is much increased. We can
thus distinguish an optimum intensity of light, to which the organisms
may be said to be attuned. Either increase or decrease from the op-
timum causes the avoiding reaction. Often the organisms are positive
when placed at some distance from a window, but become negative
when brought nearer. There is much variation among different species,
and even among different individuals of the same species, as to the
amount of light that causes this change from positive to negative. Some-
times, with a given intensity of light, half the individuals of Ulothrix
are found to be positive, the other half negative (Strasburger, /.c. p. 17).
The same individual is seen at times to be at first positive, later negative.
Some of the influences which modify the reaction to light are known.
Certain swarm spores are attuned to a stronger light in the early stages
of development than in the later stages. Specimens grown in shaded
regions seem attuned to less intense light than those living in well-
lighted cultures. That is, the organisms are attuned more nearly to
the light to which they are accustomed. But subjection to darkness
sometimes causes negative organisms to become for a short time positive.
Hematococcus is negative in a certain intensity of light, gathering at
the negative side of the drop. Now the preparation is covered and
left in the dark for a few minutes, then the cover is removed. At once
the Hematococci leave the negative side and swim toward the light
for a short distance. But this lasts only a moment. After reaching
the middle of the drop, they swim back again to the negative side. An
increase of temperature increases the tendency to a positive reaction to
strong light; a decrease of temperature has the opposite effect. Lack
of oxygen increases the tendency to a positive reaction. This is ac-
counted for by the fact that the green organisms produce oxygen in the
light. °

REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 149

A change in the intensity of light does not as a rule produce its
characteristic effect immediately, but requires a definite interval of time.
When the light is faint and the organisms are swimming toward it, if
the light is suddenly increased to an intensity to which they are nega-
tive, the swarm spores continue to swim toward it forsome time. The
interval may amount to as much as half a minute. At the end of this
period they turn and swim away from the light. Again, when the or-
-ganisms are swimming away from a strong light, a sudden decrease
in illumination causes them to become positive only. after some seconds.
But in some species there is no such delay in the effects of a change of
illumination.

To sum up, we find that the reactions to light occur in the infusoria
in essentially the same way as do the reactions to most other stimuli,
through the avoiding reaction ; that is, by the method of trying movements
in different directions. The cause of reaction is a change in the intensity
of light, — primarily that affecting the sensitive anterior end. Changes
in intensity may be produced either (1) by the progression of the or-
ganism into a region of greater or less illumination, or (2) by the swinging
of the sensitive anterior end toward or away from the source of light,
so that it is shaded at one moment and strongly lighted the next. Usually
these two classes of changes work in unison; when they are opposed, the
organism reacts in accordance with that which is stronger. When the
second class of changes above mentioned is the determining factor,
the organism continues to react by trial till these changes cease. This
results in producing orien‘ation with anterior end directed toward or
away from the source of light. In strong light the effect of an increase
or decrease of intensity is often the reverse of that observed in weak
light.

2. REACTION TO GRAVITY AND TO CENTRIFUGAL FORCE

A considerable number of infusoria have been found to react to
gravity in much the same way as does Paramecium (Jensen, 1893).
As a rule, when placed in vertical tubes, they rise to the upper end.
The following infusoria have been found to behave in this way: Among
the flagellates: Euglena, Chlamydomonas, Hematococcus, Polytoma,
Chromulina; among the ciliates: Paramecium bursaria, Urostyla.
Spirostomum ambiguum takes at times a vertical position in the water
a short distance above the bottom, with anterior end upward. Under
these circumstances it is anchored by an invisible thread of mucus, as
may be observed by passing a glass rod between it and the bottom
(Fig. 82). The stationary position oriented with reference to gravity

150 BEHAVIOR OF THE LOWER ORGANISMS

seems to be the result of a slight activity of the cilia, tending to cause
movement upward, combined with the downward pull of the thread
at the posterior end. Jensen found that Colpoda cucullus, Colpidium
colpoda, Ophryoglena flava, and Coleps hirtus showed no clear reac-
tion to gravity.

There is reason to suppose that reaction to gravity, where it occurs,
is brought about in the same manner as in Paramecium. The details
given in the account of Paramecium therefore need not be repeated here.

_As a general rule the reaction to gravity is easily masked by reactions
to other stimuli. It is shown in a marked way only when other effective
stimuli are largely absent, and in cases of conflict with other reactions,
it is usually the reaction to gravity that gives way. In some cases the
action of other agents causes the reaction to gravity to become reversed,
just as in Paramecium. Massart (1891 a) finds that this effect is pro-
duced in Chromulina by lowering the temperature to 5-7 degrees C.

A number of infusoria are known to react to centrifugal force in the
same way as to gravity. They swim in the opposite direction from
that in which the centrifugal force tends to carry them, just as Parame-
cium does. It is probable that in all cases centrifugal force could be
substituted for gravity without essential alteration of the reactions.
Schwarz (1884) found that Euglena and Chlamydomonas react to cen-
trifugal force when it is equal to about 4 the force of gravity, and con-
tinues the reaction till the centrifugal force is about 84 times gravity.
Above this they are passively carried in the direction of action of the
centrifugal force.

LITERATURE VIII
BEHAVIOR OF INFUSORIA IN GENERAL
A. Reactions to light: JENNINGS, 1904 a@; STRASBURGER, 1878; ENGELMANN,
1882; MAstT, 1906; FAMINTZIN, 1867; HERTEL, 1904; HOLT AND LEE, I901!;

HOLMES, 1903 ; OLTMANNS, 1892.
&. Reactions to gravity: JENSEN, 1893; MASSART, 1891 @; SCHWARZ, 1884.

CHAPTER IX
REACTIONS OF INFUSORIA TO THE ELECTRIC CURRENT
1. DIVERSE REACTIONS OF DIFFERENT SPECIES OF INFUSORIA

THERE is great diversity in the gross features of the behavior of differ-
ent infusoria under the action of the continuous electric current. Some
swim, like Paramecium, to the cathode; some to the anode; some take
a transverse position; some swim to one electrode in a weak current,
to the other in a strong current; some, finally, do not react at all. Yet,
in spite of this great diversity, we find the fundamental effect of the
current on the motor organs to be almost identically the same through-
out the series. In all infusoria having cilia in different regions of the
body, the cilia of the cathode region strike forward, those of the anode
region backward, just as we have seen to be the case in Paramecium.
How the organisms move under these conditions depends on the pecu-
liarities of structure and of the action system of the infusorian in ques-
tion. We shall review here the different types of behavior under the
action of electricity, endeavoring to show how each is brought about.

A. Reaction to Induction Shocks

We may again take up, first, the reactions to single induction shocks,
studied by Roesle (1902) and Statkewitsch (1903). In all infusoria
investigated the reaction to moderately strong induction shocks is es-
sentially similar to the reaction to other stimuli. The animal usually
responds to the shock by the avoiding reaction, which begins with a
reversal of the cilia in that part of the body directed toward the anode.
In some cases, however, the induction shock causes, like a weak mechani-
cal stimulus, a mere movement forward (Roesle, 1902). If the shock
is a powerful one, the body may contract in the anode region, or, in the
case of very contractile species, such as Lacrymaria and Spirostomum,
the entire body may contract. Reaction takes place most readily as a
rule when the sensitive anterior end is directed toward the anode, or
especially, according to Roesle, when the mouth opening is precisely
directed toward the anode. When the animal is in the transverse posi-
tion, it is least affected by the induction shock, and in many cases it is

Ist

152 BEHAVIOR OF THE LOWER ORGANISMS

less affected when the aboral side is directed toward the anode, than in
the opposite position.

,

B. Reaction to the Constant Current

Under the action of the constant current there are a few infusoria
which do not react at all, so faras known. This is the case, for example,
with Euglena viridis. Even with powerful currents it shows no reaction.

The larger number of free ciliate infusoria swim under the influence
of the constant current to the cathode, while a few swim to the anode
or take a transverse position. A considerable number of flagellates’
swim to the anode, though some swim to the cathode.

The reaction of the flagellates has been little studied in any precise
way. Owing to their minuteness it is usually very difficult to deter-
mine their exact movements. According to Verworn (1889 6), Trache-
lomonas and Peridinium swim to the cathode; Polytomella uvella,
Cryptomonas ovata, and Chilomonas paramecium to the anode. In
stronger currents some of the individuals of Chilomonas swim to the
cathode. The reason for the diversity in the reactions of different
flagellates has not been determined. In the case of Trachelomonas,
according to Verworn, the flagellum is strongly stimulated when directed
toward the anode. The result is that it strikes strongly in such a way
as to turn the organism around, — doubtless by a typical avoiding
reaction similar to that described on page 111 for Chilomonas. On
reaching a position with anterior end directed to the cathode, it is no
longer effectively stimulated; it therefore continues to move toward the
cathode. In Chilomonas the orientation to the electric current is known
_ to be brought about through the typical avoiding reaction. That is,
the animal turns toward the smaller lip (Fig. 72, y), till orientation is
attained (Pearl, 1900). Since in the flagellates the motor organs are all
at one end, all bear the same relation to cathode or anode, so that we
cannot expect any opposition in the action of the different flagella, such
as we find in the cilia of different regions in Paramecium. There is
thus no sign in the flagellates of that lack of codrdination or of an
apparent attempt to move in two directions at once, which we find in
Paramecium.

‘Among the Ciliata, most species, under usual conditions, turn the
anterior end to the cathode and move toward that electrode. But
Opalina moves, usually, to the anode, and Spirostomum as a rule takes
a transverse position. Certain variations in the reactions under different
conditions will be brought out later.

Among the organisms which pass to the cathode, the manner in which

REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 153

orientation takes place varies in different species. The direct effect
of the current is, as in Paramecium, to cause the cilia on the cathode
side to strike forward, while those on the anode side strike backward.

This would result, taken by es
. . . ° 2 oO
itself, in turning the animals he +
directly, by the shortest path, ay ee Y
toward the cathode. But in fl ay is
many species, as our study 0. a
of the reactions to other S

iS

stimuli has shown us, there
is a strong tendency to turn
toward one side rather than
the other, usually toward
the aboral side, — that oppo-
site the peristome. The cilia
of the peristome are usually
more powerful than those of
the remainder of the body,
so that the direction in which
the animal turns depends
largely upon the way these
cilia strike. When the peris-
tomal cilia strike strongly
backward, the organism
turns toward the opposite or
aboral side, with little regard
to the beat of the remainder
of the cilia. These peristo-
mal cilia are as a rule lim-
ited to one of the four
quarters into which the sur-
face of the body can be di-
vided, as illustrated in Fig.
too. They, of course, beat
backward when either the
end bearing them, or the side
bearing them, is directed
toward the anode (1-3, Fig.
100), so that in these positions the animal turns toward the aboral side
in order to reach the position of orientation, just as it does in response
to other stimuli. It is only when the side bearing the peristome is di-
rected toward the cathode that these cilia beat forward, and hence tend

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154 BEHAVIOR OF THE LOWER ORGANISMS

to turn the organism toward the oral or peristomal side (Fig. 100, 6).
Under these circumstances, another principle requires consideration.
Normally the peristomal cilia strike backward. When they strike for-
ward, they develop much less energy, — less turning power, — than when
they strike backward. Therefore, when in the position shown at 6,
Fig. 100, the turning is much less rapid than in other positions, and may
easily be prevented by a slight resistance. These relations will be
understood by an examination of the diagram (Fig. 100).
In Paramecium, as we have seen, the same condition of affairs is
exemplified to a certain degree, so that the organism turns toward the
oral side in all positions save from
d to j, Fig. 63. In the Hypo-
tricha (Oxytricha and _ Stylo-
+ nychia) this condition is most
typically exemplified. A large
share of the body cilia are absent
or have taken the function of legs,
tee Gimia anda the MEN the peristomel cilia are very,
action of the electric current, when the animals powerful. In almost all cases
ae in contact ih, the, gutstratum. The these organisms become oriented
to the electric current by turning
toward the aboral (right) side. It is only when the peristomal cilia are
squarely facing the cathode (Fig. 100, 6) that the animal may turn toward
the oral (left) side. In this position the peristomal cilia beat forward,
and all the cilia of the body aid in turning the organism toward the oral
side. On reaching a position with anterior end directed to the cathode the
peristomal cilia are directed forward, but their beating has become so weak
as to be almost without effect. The animal, therefore, retains this position.
When specimens of the Hypotricha are in contact with a surface, as
is usually the case, the forward beat of the peristomal cilia is often so
weak and ineffective in the transverse or oblique position (Fig. 100, 6)
that it does not turn the animal against the resistance offered by the
attachment of the ventral cilia. Such specimens, therefore, remain in
the transverse or oblique position, the anterior end usually slightly in-
clined toward the cathode, as in Fig. 101. In this position they run
forward. When the current is reversed, so that the anode lies next the
peristome, the powerful peristomal cilia strike backward. The ani-
mals, therefore, turn toward the aboral (right) side till they have again
become nearly transverse to the current. They then move forward in
the direction so indicated. Similar phenomena are at times to be ob-
served in other ciliates, not belonging to the Hypotricha. This is true,
as we have seen, even for Paramecium.

REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 155

Thus we can distinguish two factors in the turning produced by the
electric current. The first is a tendency to turn directly toward the
cathode, the second a tendency to turn toward a structurally defined
side, — usually the aboral side. The conflict of these tendencies when
the animal is in

b € aes
certain positions, a — ~~ dd
and’ their mutual
reénforcement in + wy ;
other positions,

often é give rise to Fic. 102. — Diagrams of the reaction of Colpidium to the electric
peculiar and com- current when in various positions. Based on the descriptions and

plicated phenom- figures given by Pearl (1900).

ena. Thus, in Colpidium, as described by Pearl (1900), we have the
following different methods of reacting to the electric current. (It
should be premised that Colpidium tends under ordinary conditions to
turn toward the aboral side.)

(1) When the anterior end is directed approximately toward the
anode, or in any position in which the aboral side is nearest the cathode,

c Colpidium turns toward the

\ aboral side (Fig. 102, a, b), till

b the anterior end is directed

toward the cathode. Both the

factors mentioned above coép-
/ erate to produce this result.

/ is (2) When the animal is

y nearly transverse, or is ob-

lique, with the oral side next

+ . - to the cathode, it usually

x j _. swims slowly forward, and at
cohen O8,c, Digeam of one method by which the same time gradually turns
with the oral side to the cathode. Constructed from toward the oral side till it be-
pie Seve by Peart (2900). comes oriented (Fig. 102, c-d).
The two tendencies mentioned above oppose each other in this case, and
the first one overcomes the second.

(3) But in other cases when the animal is in the position described
in the last paragraph (Fig. 103, a) it reacts in another way. It moves
forward, slowly turning toward the oral side (Fig. 103, a—b), then turns
on its long axis (b-c) (as happens in ordinary locomotion). This brings
the aboral side next to the cathode (c). Now the animal turns suddenly
toward the aboral side till the anterior end is directed toward the cathode
(Fig. 103, d). In this case, then, the two tendencies mentioned above
oppose each other till the revolution on the long axis occurs, then they
reénforce each other.

156 BEHAVIOR OF THE LOWER ORGANISMS

(4) If Colpidium is squarely transverse, with oral side to the cathode
(Fig. 104, 1), or especially if the anterior end is a little inclined toward
the anode, the organism often starts trans-
versely to the current. Suddenly it jerks its
body a little toward the aboral side (Fig.
104,1-2), then moves forward again. Again it
jerks toward the aboral side (3), again moves
forward, and repeats this behavior until the
anterior end is directed toward the anode.
Then it turns steadily toward the aboral side
till the anterior end is directed toward the
cathode (Fig. 104, 4-5). In this behavior the

2 > two tendencies mentioned oppose each other,
a as in case 2, but the second one prevails over
/ the first.
y Various combinations of these different
+0 o — reaction types may occur, making the be-

havior of Colpidium under the electric cur-
eee Lesh wosthed rent very complicated. Similarly varied be-
of reaction to the electric current havior is often. observed in other infusoria,
in Colpidium. After Pearl through the action of similar causes.
(2900). In such infusoria as Stentor, where the
peristomal cilia form a circle surrounding the anterior end, there is no
reason for such a conflict of tendencies. The peristomal cilia are
divided by an electric current coming from one side, so that the ani-
mal turns directly away from the side on which these

cilia strike backward (Fig. 105). If the anterior end Sig

is directed toward the anode at the beginning, the

animal doubtless turns as usual toward the right

aboral side. In other positions the usual method of

turning seems to have no effect on the reactions. In 4 -
Fr

Vorticella and other infusorians resembling Stentor
in the distribution of the cilia, the orientation to the
current would doubtless take place in the same direct
manner, though this has never been determined.

In Spirostomum and Opalina, the conflict of the
two tendencies mentioned above leads to certain very 6. Xo, St
remarkable and complex results. Under usual con- action of Stentor when
ditions Spirostomum takes a transverse position in Sh cones
‘the electric current, while Opalina swims to the toward the cathode,
anode. The gross features of the behavior thus differ eet se scoiieeahal
markedly from those shown by most other infusoria. effect.

REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 157

But Wallengren has shown that the effect of the current is in these in-
fusoria of essentially the same character as in others. Let us examine
briefly the facts as set forth by Wallengren (1902 and 1903).
Spirostomum (Fig. 106) is a very long, slender infusorian, easily
bent in any direction, and very contractile. The peristomal cilia are
very large and numerous, extending from the anterior end along one
side to a point behind the middle. Whether striking forward or back-
ward, the beating of these A
cilia is decidedly more effec- /_, 3
tive than that of the cilia on Scssi4a—
the opposite side of the
body. It is to this fact, . B +
taken in connection with the -X
slenderness and suppleness
of the body, that most of
the peculiarities in the reac-
tion of Spirostomum to the
electric current are due. c
In a very weak current, ;
such as does not cause con-
traction of the body, Spiro-
stomum swims to the cath- =—-
ode. The cilia on the
anodic part of the body
strike backward, those in
the cathodic region forward,
just as happens in Para-
mecium. As a result, the
animal takes a position with Fic. 106. — Diagrams illustrating reaction of
anterior end directed to the SPitostomum to the electric current. A, B, D, and
z ‘ E after Wallengren (1903).
cathode, in essentially the
same manner as does Paramecium, — usually turning to the aboral side,
but in certain cases toward the oral side. When the anterior end is
directed toward the cathode, the cilia on the cathodic half of the body
are partly directed forward, but with the weak current most of them still
strike most strongly backward. Those of the anode half of course
strike backward, so that the general result is to drive the animal
forward to the cathode. Sometimes Spirostomum under these condi-
tions comes against the bottom or other solid object; it may then nearly
or quite cease to move forward. ‘The facts thus far are quite parallel
to those observed in Paramecium.
As the electric current is made stronger, the cilia on the cathodic

aye rs
Z

158 BEHAVIOR OF THE LOWER ORGANISMS

half of the body strike more powerfully forward, and at a certain strength
their effect, tending to drive the animal backward, becomes about equal
to that of the anodic cilia, tending to drive it forward. The result is
that the animals move neither forward nor backward, or only very
slowly in one direction or the other. They thus sink to the bottom
before much progress has been made. Now, if in this position the an-
terior end is directed toward the cathode (Fig. 106, A), of course the
cilia of the anterior (cathodic) half of the body tend to push the animal
backward, while those of the opposite half tend to push it forward. This
push in opposite directions bends the supple body near its middle. More-
over, in the cathodic half the peristomal cilia have a more powerful for-
ward stroke than do the ordinary cilia on the opposite side, hence the
anterior half of the body tends to bend toward the peristomal or oral
side. The general result is that the animal is bent into the position
shown in Fig. 106, B. The bending of the anterior part of the body
toward the oral side continues, until this part of the body becomes trans-
verse to the current (Fig. 106, C). The body may now become com-
pletely straightened (Fig. 106, D), or it may not. But in either case
the peristome is now turned toward the anode. The powerful peris-
tomal cilia therefore strike backward, causing the anterior end to swing
toward the aboral side, directing it again toward the cathode, as indi-
cated by the arrow in D. On becoming directed toward the cathode,
the original condition (Fig. 106, A) is restored. The animal therefore
again takes the positions B, C, and D. It thus continues to squirm
from side to side. But during its movements Spirostomum, like Para-
mecium, frequently revolves on its long axis. This often happens when
in the position shown in Fig. 106, C, so that the animal becomes placed
transversely to the current, with peristome to the cathode (Fig. 106, E).
In this position the peristomal cilia are directed forward and have there-
fore comparatively little motor effect. If at the same time the animal
comes in contact with the bottom, the contact reaction may overcome
for a time this slight motor effect, so that the animal lies nearly quiet,
in the transverse position. If now the current is reversed, so that the
peristome is at the anode (Fig. 106, D), the animal at once swings again
toward the aboral side. Even if the current is not reversed, the animal
usually does not remain long in the position shown at E. The peri-
stomal cilia being more effective than the opposing ones, gradually swing
the anterior half toward the oral side. Soon a bending takes place
again, as in B, and the organism is forced to squirm about from side
to side, as before.

Thus Spirostomum finds in a strong current no position of equilib-
rium, because the peristomal cilia have always a more powerful effect

REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 159

than the opposing ones, and because the opposed action of the cilia on
the anodic and cathodic halves of the body soon bends the slender body.
It thus squirms about from one side of the transverse position to the
other, taking many shapes besides those figured. It remains quiet only
for certain periods in the transverse position with peristome to the cath-
ode, when it is in contact with a surface: this is a result of the inter-
ference of the contact reaction with the reaction to the electric current.
Under the action of the current alone, the reaction of Spirostomum does
not tend to bring it to a position where it is not effectively stimulated,
for no such position exists. In this respect the electric stimulus shows
again a marked contrast with other stimuli.

In Opalina ranarum the first marked effect of the electric current is
to cause the animals to swim to the anode instead of to the cathode.
Its reaction seems thus in striking contrast with that of other ciliate
infusoria. We must examine the reaction in Opalina, following Wallen-
gren (1902), to see how this result is brought about.

Opalina is a large, flat, disk-shaped, parasitic infusorian, living in
the large intestine of the frog. For experimental work it is examined
in physiological salt solution, as it soon dies in water. There is no
mouth, since food is obtained by absorption over the entire body sur-
face. The body is closely set with fine cilia. The anterior end of the
body is more pointed than the posterior. From the anterior portion
there extends backward at one edge a convex region, ending at a sort
of notch in the middle of the body (Fig. 107, x). This convex region
is set with cilia having, as we shall see, a somewhat different function
from those of the remainder of the body. The side bearing this con-
vexity is usually known as the right side.

Opalina swims with anterior end in front, at the same time usually
revolving on its long axis. When stimulated by contact with a solid,
or in other ways, it turns toward the side bearing the convexity — the
right side. Observation shows that this movement is due to the fact
that the cilia on the convexity of the right side now strike forward in-
stead of backward, thus necessarily turning the animal toward the side
bearing them. In this way the typical avoiding reaction of Opalina is
produced.

If a preparation of Opalina in physiological salt solution is sub-
jected to the action of a weak electric current, the animals swim to the
anode. Examining the individuals, it is found that the cilia on the
anode half of the body strike backward, those on the cathode half for-
ward, exactly as in Paramecium. Why then does Opalina swim to the
anode instead of to the cathode?

The secret of this difference lies in the following facts. The cilia

160 BEHAVIOR OF THE LOWER ORGANISMS

of the convexity of the right side (Fig. 107, x) are very easily reversed
by a weak current. The cilia of the opposite side, on the other hand,
are little affected by a weak current. Their usual backward stroke is
decreased in power, and doubtless some of the cilia are reversed, but the
general effect of their action is still to drive the animal forward. Let
us suppose that the Opalina is at first transverse to the electric current,

with right side to the cathode, as in Fig. 107, 1. As soon as the current.

Fic. 107. — Diagrams of the movements of the cilia, and of the direction of turning, in the
reaction of Opalina to the electric current. After Wallengren (1902).
begins to act, the cilia of the right (cathodic) side become directed for-
ward, while those of the left (anodic) side remain directed backward.
The result is of course to turn the animal to the right, toward the cath-
ode. Thus the specimen passes through the position shown in Fig.
107, 2, and comes into a position with the anterior end directed toward
the cathode (3). The cilia of the anterior part of the body are now
directed partly forward, those of the posterior half backward. In this
position, as we know, Paramecium remains; indeed, the whole reaction
thus far is essentially like that of Paramecium. But in Opalina, so long

REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 161

as the current is weak, only the cilia on the convexity of the right side
strike powerfully with their reversed stroke, — these being the cilia that
are reversed in the usual avoiding reaction. The other reversed cilia
strike only weakly. In consequence the animal must turn toward the
right side, reaching the position shown in Fig. 107, 4.. Here most of
the strong cilia x of the convexity are still striking forward, hence the ani-
mal still turns toward the right. A little beyond 4, —between this and
5, — the animal reaches a position where the tendencies to turn in oppo-
site directions are equdl.* But the turning which has been initiated in
positions 1-4, as a rule has given the animal sufficient momentum to
carry it past this dead point, so that it reaches the anode pointing posi-
tion (Fig. 107, 7). Here the cilia of both sides of the anterior end are
directed backward. When striking backward the cilia x of the convexity
are no more powerful than those of the opposite side. Hence there is
now no tendency to turn farther, and the anode-pointing position is
retained. Since the backward stroke of the anterior cilia is more power-
ful than the forward stroke of the reversed posterior cilia, the animal is
carried forward to the anode. Thus in a weak current the position with
anterior end directed to the anode is the stable one, so that in the course
of time, after some oscillation, the animals reach this position and swim
toward the anode.

Now if the current is considerably increased in strength, the cathodic
cilia are caused to strike more strongly forward than before. Their
motor effect therefore nearly equals that of the anodic cilia, so that the
_ forward movement toward the anode is made much slower. If at the
time the current is made the Opalina is in an oblique position, as will
usually be the case, or if as a reaction to other stimuli during the passage
of the current it passes out of the position with anterior end to the anode,
then another effect is produced. Suppose it comes thus into the position
shown in Fig. 107, 8. Then the larger number of cilia tend to turn it to
the right, as is shown by the arrows at 8. It thus comes into position 1,
where all the cilia assist in turning it to the right; it continues in the
same way through position 2 to position 3, with anterior end pointing
to the cathode. With a weak current, as we have seen, this position
is not a stable one; the stronger forward beating of the cilia on the
convexity of the right side cause the animal to continue to turn to the
right. But with a stronger current this becomes changed. Since even
in a weak current the cilia of this’ convexity strike as strongly forward
as they can, their forward stroke is not increased when the current is

1Tf the animal at this point or earlier turns’ on its long axis, as it frequently does in its
usual locomotion, it must now swing back through the cathode-pointing position, till it
again reaches a position corresponding to 4 or 5.
M

162 BEHAVIOR OF THE LOWER ORGANISMS

made stronger. But as the current is increased, the forward stroke of
the cilia on the left side of the anterior half of the body becomes more
powerful, — just as happens with all the anterior cilia in Paramecium.
Hence, when the current reaches a certain strength, the cilia of the left
side, in an Opalina pointing toward the cathode, beat as strongly for-
ward as do those of the right side. There is then no cause for turning
toward either the right or the left. The position with anterior end
directed toward the cathode has become a stable one. Thus, when a
strong current is passed through a preparation of Opalinz, most of them
become directed after a time toward the cathode, and swim slowly in that
direction. A number may be at first directed toward the anode, but. as
soon as these by any chance get out of the anode-pointing position, they
also become directed toward the cathode.

With a still more powerful current the Opaline retain nearly or
quite the position with anterior end to the cathode, but move backward
(or sometimes sideways) toward the anode. Wallengren believes that
this is a passive movement due to the cataphoric action of the electric
current. In Paramecium, as we have seen, there is a similar move-
ment under these conditions, but due to the fact that the cathodic cilia
beat more effectively forward than do the anodic cilia backward.

Thus altogether we find that in Opalina the electric current acts op
the motor organs in fundamentally the same way as in Paramecium.
But owing to peculiarities of the action system of Opalina, this results,
with a weak current, in movement forward toward the anode; with a
stronger current in movement forward toward the cathode; with a still
stronger current in movement backward or sideways toward the anode.

2. SUMMARY

Reviewing our results as to the effect of the continuous electric cur-
rent on the ciliate infusoria, we find a complete agreement throughout
in the action of the current on the motor organs, with the greatest pos-
sible diversity in the resulting movements of the animals. In all cases
the cilia in the anode region strike backward, as in the normal forward
movement, while the cilia of the cathode region are reversed, striking
forward. With different strengths of current, and with infusoria of
different action systems, this results sometimes in movement forward to
the cathode; sometimes in movement forward to the anode; sometimes
in a cessation of movement, the anterior end continuing to point to the

cathode; sometimes in a backward movement to the anode; sometimes —

in a position transverse to the current, the animal either remaining at
rest or moving across the current. These variations depend upon the

REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 163

differences in the strength of beat of the cilia of different regions of the
body under currents of different strength. The different effects pro-
duced may be classified, as to their causes, in the following way :—

1. The orientation with anterior end to the cathode is due to the
fact that the cilia of the cathodic side strike forward; of the anodic side
backward. This may be assisted or hindered by the usual tendency of
the organisms to turn when stimulated toward a certain structurally
defined side.

2. The movement toward the cathode in weak or moderate currents
is due to the fact that under these conditions the backward stroke
of the anodic cilia is more powerful than the forward stroke of the
cathodic cilia. ’

3. The cessation of progression in a stronger current, with reten-
tion of the cathode-pointing orientation, is due to the fact that as the
current is increased the forward stroke of the cathodic cilia becomes
more powerful, till it equals the backward stroke of the anodic cilia.

4. The swimming backward toward the anode in a still stronger cur-
rent is due to a continued increase in the power of the forward stroke of
the cathodic cilia, so that they overcome the tendency of the anodic cilia
to drive the animal forward. (In Opalina, Wallengren believes that this
backward movement is due, at least partly, to the cataphoric effect of
the current.)

5. The unstable transverse position seen in some cases (Spiro-
stomum) is due primarily to the fact that the cilia of one side of the
elongated body are more powerful, when striking either backward or
forward, than are the corresponding cilia of the opposite side. As a
result, neither the position with anterior end to the cathode nor that
with anterior end to the anode is a stable one, and the animal is com-
pelled to oscillate about a transverse position. This result is accen-
tuated by the slenderness and suppleness of the body in these species.

6. The orientation with anterior end to the anode seen in certain
cases (Opalina in a weak current) is due to the fact that the cilia of one
side of the anterior half of the body are more readily reversed than the
opposing cilia, and their reversed stroke is more powerful, though their
usual backward stroke is not. The result is that the position with an-
terior end to the cathode becomes unstable, while the position with
anterior end to the anode is stable so long as accidental causes do not
produce slight deviations from it.

7. The transverse or oblique position, at rest or with movement
athwart the current, is due to interference between the contact reaction
and the effect of the current. This position is maintained only when
the more powerful cilia of the peristome are striking forward; that is,

164 BEHAVIOR OF THE LOWER ORGANISMS

when the peristome is directed toward the cathode. When the peri-
stomal cilia are thus striking forward, their action is comparatively in-
effective, so that it does not overcome the attachment to the substratum,
in the contact reaction.

3. ‘THEORIES OF THE REACTION TO ELECTRICITY

What is the cause of the reaction to the electric current? The most
striking phenomenon in a general view is usually a movement of the
organisms en masse toward the cathode or anode. It is well known that
the electric current has the property of carrying small bodies suspended
in a fluid toward the cathode or anode, depending on the conditions.
This phenomenon is commonly known as cataphoric action, or as elec-
trical convection. When the movement of small organisms toward one
of the electrodes is mentioned, the first thought that comes to mind is
of course the possibility that they are thus passively carried by the cata-
phoric action of the current. But this view can be maintained only on
_ the basis of an extraordinarily superficial acquaintance with the facts.
Careful study shows, as we have seen, that the current has definite and
striking effects on the cilia, and that it is to these effects that the peculiari-
ties of movement under the action of the current are due. Nevertheless,
the theory that the phenomena are passive movements due to the cata-
phoric action of the current continues to be brought gravely forward at
intervals, and doubtless this will continue. The fundamental fallacy
of this theory is the idea that we must account in some way by the action
of the current for the fact that the organisms move. This is quite un-
necessary, for they move equally without the action of the current. The
movement is spontaneous, so far as the electric current is concerned. It
takes place by the agency of the motor organs of the animal, driven by
internal energy, and acting upon the resistance furnished by the water.
It is only the changed direction of the movement that the electric cur-
rent must account for. There is no place for the agency of the cata-
phoric action in transporting the animals, for they are visibly transport-
ing themselves, just as they were before the cataphoric action began.
It is absolutely clear that the movements of the cilia, described in the
preceding pages, are at the bottom of the observed behavior, and any
explanation of the reaction to electricity must account for the influence
of this agent on the cilia. This the theories of passive movement by
cataphoric action make no attempt to do.

The clearest disproof of the theory that the movement is a passive
one due to cataphoresis is of course the well-established positive proof
that the movement is an active reaction of the organism. But the theory

REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 165

can be disproved on other grounds. Statkewitsch (1903 a) shows that
dead or stupefied Paramecia that are suspended in viscous fluids are not
moved by cataphoric action, while living Paramecia in the same fluids
swim to the cathode. Dead or stupefied Paramecia placed in water in
a perpendicular tube through which an electric current is passed sink
slowly and steadily to the bottom, whatever the direction of the current,
while living specimens pass upward when the cathode is above. If the
anode is above and a very strong current is used, the living animals swim
backward to the anode, as described on page 98. They therefore move
upward against gravity, while dead or stupefied specimens with the same
current sink slowly to the bottom of the tube. It is thus clear that neither
the forward movement to the cathode nor the backward movement
toward the anode is directly due to the cataphoric action of the current,
for this action is not capable of producing the observed movements. ~

The cataphoresis might of course act in some way as a stimulus to
induce the observed active movements of the cilia. This is apparently
the view toward which Carlgren (1899, 1905 @) and Pearl (1900) are
inclined. This is of course a theory of a radically different character
from that which we have been considering. Just how this effect would -
be produced through the known physical action of the current has not
been shown.

Coehn and Barratt (1905) hold that Paramecia in ordinary water
become positively charged, through the escape into the water of the
negative ions of the electrolytes which the body holds, while the positive
ions are retained. As a result of this positive charge, the electric cur-
rent tends to carry the animals to the cathode; the infusoria are held
to follow this tendency and swim with the pull of the current toward the
cathode. In a solution containing more electrolytes, it is held that the
positive ions escape from the protoplasm; hence the animals become
negatively charged. They therefore pass to the anode when placed in
a solution of sodium chloride or sodium carbonate. This theory leaves
unaccounted for precisely the essential feature of the reactions, — the
cathodic reversal of the cilia. It likewise fails to account for the fact
that as the current becomes stronger the passage to the cathode ceases
and the animals begin to swim backward to the anode, and for the
further fact that individuals which have become accustomed to a solu-
tion of sodium chloride or carbonate no longer swim to the anode, but
pass to the cathode as usual. These facts appear to be absolutely fatal
to the view under consideration. Little is to be hoped of any theory
that neglects what is clearly the fundamental phenomenon in these
reactions, — the cathodic reversal of the cilia.

Another theory has held that the reaction to the electric current is

166 BEHAVIOR OF THE LOWER ORGANISMS

due to the electrolytic effect of the current on the fluid containing the
animals (Loeb and Budgett, 1897). The water of course contains elec-
trolytes. These are separated by the current into their component ions,
and the products of this electrolysis may be deposited on opposite poles
of a body immersed in the fluid. There is some reason to suppose that
an alkali may be deposited on that portion of the surface of the infusorian
where the current is entering its protoplasm (the anodic surface), an
‘acid where it is leaving the protoplasm (the cathodic surface). The
relative amount of such action is unknown, but the suggestion is made
that the observed effects of the current are due to these chemicals. This
very interesting and suggestive theory seems, however, not to be supported
by other known facts. The effects of different chemicals on the ciliary
action are known, and it is not
true that acids produce con-
tinued reversal of the cilia, alka-
lies the opposite effect, as would
be necessary in order to make
~~ this explanation satisfactory.
Any effective chemical, either
acid or alkali, produces, as we
know, the avoiding reaction,
with its succession of coérdinated
_ Fic. 108.— Diagram of the effects of the elec- changes in the ciliary movements.
where the cilia are directed forward and backwara, Again, as Ludloff (1895) and
respectively, do not correspond to the regions where Statkewitsch (1903) show, the
eee eee ereenng the body. characteristic anodic and cath-
odic effects do not correspond throughout to the regions where the cur-
rent is entering or leaving the protoplasm. If a Paramecium has an
oblique position, as in Fig. 108, the current enters the body on the entire
left side, and leaves the body on the entire right side. Hence, on the
theory we are considering, all the cilia of the left side ought to act
alike, and in the opposite manner from the cilia of the right side.
But this is not true. On the left side the cilia of the region b beat for-
ward, those of c backward; on the right side the cilia @ strike forward,
dbackward. A similar distribution of the discharge of trichocysts under
the influence of the induction shock is shown to exist by Statkewitsch.
The distribution of the effects of the current on the cilia and on the
trichocysts therefore does not correspond to the distribution of the regions
where the current is entering and leaving the protoplasm; hence the
latter cannot explain the former.
Another theory, somewhat less definite than the one last mentioned,
but widely accepted, is the following. The electric current is conceived

REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 167

to have a polarizing effect on the organism, resulting in the different
action of the cilia on the two halves. At the anodic half the current
is considered to cause a backward movement of the cilia, or “contractile
stroke”; at the cathodic half, a forward movement or ‘expansive
stroke’? (Verworn, 1899; Ludloff, 1895). The precise cause of this
action is not given, but as supporting the possibility of this view, the
experiments of Kiihne (1864, page 99) and Roux (1891) on the polariz-
ing effects of the current may be cited. Kiihne showed that the violet-
colored cells of Tradescantia become under the influence of the electric
current red at the anodic end, green at the cathodic end, — indicating
that the anodic end becomes acid, the cathodic end alkaline. Roux
showed that under the electric current the frog’s egg becomes divided
into two halves of different color. Furthermore, the two halves of a
cell in the electric current become physically somewhat different, owing to
the cataphoric action. There is a tendency for the fluids of the body
to be carried to one end, — the cathodic, — while the solids are carried
to the other, —the anodic. As a result of such chemical or physical
polarization, or of both, it is then conceivable that the body of the in-
fusorian may become divided into two halves, differing in such a way
that the cilia act in opposite directions. On this view the backward
stroke of the cilia on the anodic half of the body is as much a specific
effect of the current as is the forward stroke of the cathodic cilia. Op-
posed to this view is the consideration that the action of the anodic cilia
is as a matter of fact not different from that in the unaffected animal,
and the further fact that the cathodic effect is limited, in a weak cur-
rent, to only the cathodic tip of the animal. If both the backward and
the forward positions of the cilia are specific effects of the current, it
is difficult to see why the former should prevail so strongly over the
latter in a weak current. On the other hand, if we consider the cathodic
action alone as a specific effect of the current, interfering with the normal
backward stroke of the cilia, then it becomes at once intelligible that
this interference should be least in a weak current, and should increase
as the current becomes more powerful. In producing its characteristic
effect chiefly at the cathode, the action of the electric current on in-
fusoria agrees with its action on muscle, as Bancroft (1905) has recently
pointed out.

The most thorough study of the fundamental changes produced by
the electric current is that made by Statkewitsch (1903 @), and his con-
clusions are entitled to high consideration. Statkewitsch subjected Para-
mecia that had been stained in the living condition with certain chemical
indicators, — neutral red and phenol-phtalein, — to the influence of the
electric current. He found that the current caused chemical changes

168 BEHAVIOR OF THE LOWER ORGANISMS

within the protoplasm, the endoplasmic granules and vacuoles becoming
more alkaline in reaction. Statkewitsch therefore concludes that the
peculiar effect of the electric current on the cilia is due to a disturbance
in the usual equilibrium of the chemical processes taking place in the
protoplasm. The results of this disturbance are first shown, so far as
the ciliary action is concerned, in the cathodic region, spreading thence
over the remainder of the body, as illustrated in Fig. 61.

For any satisfactory theory of the reaction to the electric current,
one thing is essential; it must account for the cathodic reversal of the
cilia. It is perfectly clear that this is the characteristic feature of this
reaction, and a theory that will account for this reversal will at once
clear up the curious and apparently contradictory effects produced under
various conditions. Theories which do not take this into account are
at the present time anachronisms; they fail to touch the real problem.

Whatever be the cause, it is clear that the behavior of infusoria under
the action of the electric current differs radically from the behavior under
other conditions. The position taken by the organism is not attained
by trial of varied directions of movement, as in the reactions to most
other stimuli, but in a more direct way. Different parts of the body
are differently affected by the current, so that the behavior is not co-
ordinated and directed toward a unified end, as in the reactions to other
stimuli. The motor organs of the'different parts of the body tend to
drive the animal in different directions. The movement actually oc-
curring is a resultant of these differently directed factors. It is there-
fore sometimes in one direction, sometimes in another, depending on
the relative strength of the opposing factors. The animal thus does
not approach an optimum nor cease to be stimulated, whatever the
direction taken. Sometimes indeed no position of even comparatively
stable equilibrium is possible (Spirostomum).

These peculiarities of the reaction to the electric current are due to
the forced reversal of the cilia in the cathodic region of the body, — an
effect not produced by any other agent. If the current produced only
its anodic effect, the reaction to electricity would be, so far as the evi-
dence indicates, precisely like that to other agents. The cathodic re-
versal of the cilia interferes with the normal behavior of the organism.
Thus the action of the infusoria under the electric current is not typical
of the behavior under other stimuli. It may be compared to the be-
havior of an organism that is mechanically held by clamps and thus
prevented from showing its natural behavior. It is interesting to note
that this cramped and incoherent behavior is found only under the in-
fluence of an agent that never acts on the animals in their natural exist-
ence. The reaction to electricity is purely a laboratory product.

' REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 169

LITERATURE IX
REACTIONS OF INFUSORIA TO ELECTRICITY

A. Reactions to induction shocks: ROESLE, 1902; STATKEWITSCH, 1903; Brru-
KOFF, 1899. ;

B. Reactions to the constant current: STATKEWITSCH, 1903 a, 1904; WALLEN-
GREN, 1902, 1993; PEARL, 1900; VERWORN, 1889 a, 1889 4, 1896; LOEB AND Bup-
GETT, 1897; DALE, 1901; CARLGREN, 1899, 1905 ; BANCROFT, 1905; COEHN AND
BARRATT, 1905.

CHAPTER X

MODIFIABILITY OF BEHAVIOR IN INFUSORIA, AND BEHAVIOR
UNDER NATURAL CONDITIONS. FOOD HABITS

1. MOpIFIABILITY OF BEHAVIOR

WE have seen that in Paramecium the behavior varies to a certain ex-
tent in different individuals or under different conditions. Similar varia-
tions might be described for other free swimming infusoria. But these
observations do not tell us whether the behavior may change in the same
individual or not. Does a given individual always react in the same
way to the same stimulus under the same conditions? Or may the
individual itself change, so that it behaves differently even when the
external conditions remain the same, — as we know to be the case in
higher animals? To answer these questions it is necessary to follow
continuously the behavior of a single individual, and this can be done
most satisfactorily in attached organisms, such as Stentor and Vorticella.
We shall base our account on the usual behavior of Stentor reselii, which
illustrates well the points in which we are at present interested.

Stentor reselii Ehr. (Fig. 109) is a colorless or whitish, trumpet-
shaped animal, consisting of a slender, stalklike body, bearing at its
end a broadly expanded disk, the peristome. The surface of the body
is covered with longitudinal rows of fine cilia, while the edge of the disk
is surrounded by a circlet of large compound peristomal cilia or mem-
branellez. These make a spiral turn, passing on the left side into the
large buccal pouch, which leads to the mouth. The mouth thus lies
on the edge of the disk, nearly in the middle of what may be called the
oral or ventral surface of the body. The smaller end of the body is
known as the foot; here the internal protoplasm is exposed, sending
out fine pseudopodia, by which the animal attaches itself.

Stentor reselii is usually attached to a water plant or a bit of débris
by the foot, and the lower half of the body is surrounded by the so-called
tube. This is a very irregular sheath formed by a mucus-like secretion
from the surface of the body, in which are embedded flocculent materials
of all sorts. It is frequently nearly transparent, so as to be almost in-
visible. Stentor reselii is found in marshy pools, where much dead
vegetation is present, but where decay is taking place only slowly.

170

MODIFIABILITY OF BEHAVIOR 171

In the extended animal the peristomal cilia are in continual motion.
When finely ground India ink or carmine is added to the water, the
currents caused by the cilia are seen to be as follows: The mouth of
the animal forms the bottom of a vortex, toward which the water above
the disk descends from all sides (Fig. 109). Only the particles near

eee treme.

Fic. 109. — Stentor reselii, showing the currents caused by the cilia of the peristome.

the axis of the vortex really strike the disk; those a little to one side
shoot by the edges without touching. Particles which reach the disk
pass to the left, toward the buccal pouch, following thus a spiral course.
Reaching the buccal pouch, they are whirled about within it a few
times; then they either pass into the mouth, at the bottom of the pouch,
or they are whirled out over the edge of the pouch, at the mid-ventral
notch. In the latter case they usually pass backward along the mid-
ventral line of the body (Fig. 109, a), till they reach the edge of the tube.
To this they may cling, thus aiding to build up the tube.

When stimulated, Stentor reselii may contract into its tube, taking
then a short oblong or conical form (Fig. 110). Such contractions do

Ket

eeult

172 BEHAVIOR OF THE LOWER ORGANISMS

not as a rule take place save in response to well-marked stimuli. When
not disturbed in any way, the animal remains extended, with cilia in
active operation.

Let us try the effect of disturbing the animal very slightly. While
the disk is widely spread and the cilia are actively at work, we cause a
fine current of water to act upon the disk, in the
following way. A long tube is drawn to a very fine
capillary point and filled with water. The capillary
tip is brought near the Stentor, while the long tube.
is held nearly perpendicular... The. pressure..causes
a jet of water from the tip to strike the disk. ofthe
animal. Like a flash it.contracts.into.its.tube...InW.

‘ “about half a minute it extends again, and the cilia

IG. 110.—— Stentor ; INT,

reselii contracted into resume their activity. Now we.cause. the current.to
its ‘tube. act again upon the disk. This time the animal does
not contract, but continues its normal activities without regard to
the current of water. This experiment may be repeated on other indi-
viduals; invariably they react to the current the first time, then no
longer react. The same results are obtained with other fixed infuso-
ria: Epistylis and Carchesium. By using other very faint stimuli,
such as that produced by touching the surface film of the water close
to the organism, or by slightly jarring the object to which it is at-
tached, the same results are obtained. To the first stimulus they,
respond sharply,...to.the.second and following ones they do not respond
at all, even if long continued.

Thus the organism_becomes changed in some way after its. first
reaction, for.to.the same stimulus,. under.the.same.external conditions,
it no longer reacts. What is the nature of this internal change? The_

first suggestion that rises to the mind in explanation of such a cessation

of reaction is that.it-may-be.due_to fatigue. The distinction between
fatigue and other changes of condition is an important one, for the
following reason... Fatigue.is.due.to.what may be called a failure. It
is an imperfection inherent perhaps in the nature of the material of
which organisms are composed, preventing them from doing what might
be to their advantage. Changes of reaction due to other causes might
on the other hand be regulatory, tending to the advantage of the or-
ganism. Higher animals often react strongly by a “start,” to the first
incidence of sudden harmless stimuli,.then-no longer react, and_this
cessation is evidently a regulation of behavior that is to the interest of.
the organism. We must then determine-whether the failure of the in-
fusorian to react.to the-second stimulation is.due to fatigue or to some
other cause.

MODIFIABILITY OF BEHAVIOR 173

It seems improbable that the change of behavior is due to fatigue,
since the change occurs after but a single stimulation and a single reac-
tion. It could hardly be supposed that these would fatigue the animal
to such an extent as to prevent further contractions. And if we use
stronger stimuli, we find that the animal continues to contract succes-
sively every time the stimulus is applied, for an hour or more. It is
evident that the failure to contract after the first stimulation cannot be

due to fatigue of the contractile apparatus. A

If we make the stimulation somewhat stronger than in our first ex-
periments, as may be done by touching the animal lightly with a. a_capil-
lary glass rod, the behavior is a little different. The animal may react
the first and second times, then cease to-react,.or-it-may_react_half.a
dozen times, or. more,-then-cease. If we continue.the stimuli,.we-find-a
change i in.the behavior. The animal instead of contracting bends.into
a new position, and it may do this repeatedly. This shows that the fail-
ure_to contract is not due to a failure to perceive the stimulus, — in.
other words, to a fatigue _ of the _perceptive power, — for the bending.
into a new position shows ‘that the stimulus i is perceived, though the
reaction differs from the first one.

Our_results thus. far show that after responding once or a few times _
to_very..weak..stimulation,.the.organism.becomes changed, so-that it
no longer reacts as before, and that this change is.not.due.to fatigue,
either_of the contractile apparatus or of the perceptive power. ‘The.

phe

ee
>

behavior may then be of the same-regulatory. character.as.is.the similar.

behavior in higher animals. Indeed, so far as the objective evidence.
goes, this behavior in Stentor precisely resembles..that..of.higher ani-
mals, and is to the same degree.in. the interest.of.the.organism,

With still stronger stimulation, produced by touching the animal
with the capillary glass rod, another curious phenomenon often shows
itself. The animal may react to each of the first half dozen strokes,
then cease to.react; then after_a few more strokes.reactagain, then.
cease to react till_a large number have been given, and so continue.
A typical series, giving the number of strokes before contraction is
produced, is the following, obtained from experiments with an individ-
ual of Epistylis : —

I — 22 — 1o— 3 —3 — I — I — 22 — §9 — 125 (continuous blows
for one minute) — (3 minutes) — (14 minutes) — (4} minutes).

During such experiments the organism, when_it does not contract,
continually changes its position, as if trying to escape the blows. The

reason for the contraction at irregular intervals which become longer
as the experiment continues, is not clear. Possibly fatigue may have _

something to do with this matter.

;

174 BEHAVIOR OF THE LOWER ORGANISMS

The stimuli with which we have thus far dealt are not directly in-
jurious, and do not interfere inthe. long_run with the normal functions
of the organism,. so.that the powerof becoming accustomed to them |
and ceasing to react is useful, Let us now examine the behavior under

ar nls _conditions which a1 are harmless when acting for a short time, but which,
but when continued, do ierfere with the normal functions. Such condi-
witi ge ytions may be produced by bringing a large quantity of fine particles,
: “~~ such_as India ink or carmine, by means.of.a_ capillary pipette, into the
water currents which are carried to the disk of Stentor, (Fig. 111).
Under these circumstances the normal movements are at first not
changed. The particles of carmine are taken into the pouch and into

- the mouth, whence-they.pass.into the internal
protoplasm. If the cloud of particles is very
dense, or if it is accompanied by.a slight. chem-
ical_stimulus, as_is usually the case with the
carmine grains, this behavior. lasts but.a_short
time; then a_ definite reaction supervenes.
The animal bends to one side — always, in Keac
the case of Stentor, toward the aboral side.
It thus as a rule avoids the cloud of particles,
unless the latter is very large. This simple
method of reaction turns out to be more
effective in getting rid of stimuli of all sorts
than might be expected. If the first reaction
is not successful, it is usually repeated one or" AgDIA
more times. This reaction corresponds closely” yeact
with the “avoiding reaction” of free-swim-
ming infusoria, and like the latter, is usually
accompanied by revolution on the long axis,
‘— the animal twisting on its stalk two or three
times as it bends toward the aboral side.

Fic. r11.—A cloud of car- If the repeated turning toward one_side
mine is introduced into the water :
currenis’ ‘passing to ‘the ‘mouth does not relieve th the animal, so thatthe parti- ol y
of Stentor. cles of carmine.continue-to-come.inadense » 2
cloud, another reaction is tried. The ciliary movement is suddenly ~ , wa
reversed in direction, so that the particles against the disk and in the
pouch are thrown off. The water current is driven away from the
disk instead of toward it. This lasts but an instant, then the current
is continued in the usual way. If the particles continue.to.come,.the
reversal is repeated.two_or three times.in.rapid.succession. If-this
fails to relieve the organism, the next_reaction — contraction — usually

supervenes. aie wr tmtrech™@m

MODIFIABILITY OF BEHAVIOR 175

Sometimes the reversal of the current takes place before the turn-
ing away described first; it may then be followed by the turning away.
But usually the two reactions are tried in the order we have given.

If the Stentor does not get rid of the stimulation in either of the -
. ways just described, it contracts into its tube. In this way it of course
escapes the stimulation completely, but at the expense of suspendin
its activity and_ losing all opportunity to obtain food. The animal
usually remains in the tube about half a minute, then extends. When
its body has reached about two-thirds its original length, the ciliary
disk begins to unfold and the cilia to act, causing currents of water to
reach the disk, as before.

We have now reached a specially interesting point in the experi-
ment. Suppose that the water currents again bring the carmine grains.
The stimulus and all the external conditions are the same as they were
at the beginning? Will the Stentor behave as it did at the beginning?
Will it at first not react, then bend to one side, then reverse the current,
then contract, passing anew through the whole series of reactions?
Or shall we find that it has become changed by the experiences it has aA Nore
passed through, so that it will now contract again into its tube as soon Coyne
as stimulated ?

We find the latter to be the case. As soon as the carmine again

reaches its ts disk, it a at _once_contracis again. This may be repeated

minutes. Now the ‘cciaal after each contraction sito a little longer

in the tube than it did at first. Finally it ceases to extend, but contracts br<@ &,
repeatedly and violently wl while still enclosed in its tube. In this way “0°
the attachment of its foot to the object on which it is situated is broken,

and the animal i is free. Now it leaves its tube and swims away. In_

leaving the tube it may swim forward out of the anterior end of the tube;

but if this brings it into the region of the cloud of carmine, it often forces

its way backward through the substance of the tube, and thus gains the

outside. Here it swims away, to form a new tube elsewhere.

While swimming freely after one Ss AoA 4
characteristic behavior of the free-swiffiming infusoria, such as P Pave=
mecium. Upon this, therefore, we need not dwell, passing at once to ““ ib
the behavior in becoming reattached and forming a new tube.

On coming to the surface film of the water, or the surface of solid yr

bjects, the free-swimming Stentor behaves in a peculiar way. It »*”

objects, the tree Pea
applies its partially unfolded disk to the surface and_creeps rapidly ss

ea hecovwt

over it, the ventral side of the body being bent over close to the pays

surface. It may thus creep over a heap of débris, following all the ©
irregularities of the surface rapidly and neatly, seeming to explore it

176 BEHAVIOR OF THE LOWER ORGANISMS

thoroughly. This may last for some time, then the animal may leave
the débris and swim about again. Other heaps of débris or the sur-
faces of solids are explored in the same way. Finally, after ten or twenty
minutes or more, one.of these-is.selected forthe formation of a new tube.
It may be seen that-as-the Stentor moyes about a viscid mucus is_se-
creted over the surface of the body. To this mucus particles of débris
stick and are trailed behind the swimming animal. In a certain region,
perhaps between two masses of débris, the animal stops and begins. to
move backward and forward with an oscillatory motion, through a dis-.
tance about two-thirds its. contracted length. This movement, in pre-.
cisely the same place, is kept up for about two minutes, while the mucus
4 .. from the. surface is. rapidly. secreted.
3%) The movement compacts this mucus
into a short tube or sheath, — the tube
in which the Stentor is to live. The
process is represented in Fig. 112.
Next the tip of the foot is pressed
against the débris at the bottom of the
iat tube. There it adheres by means of
Fic. 112. — Oscillating movement of fine pseudopodia sent out from the in-
Stentor, by which it forms a new tube.
1-2, alternating positions. @, the secreted ternal protoplasm. Now the Stentor
mucus; 6, masses of débris. extends to full length, and we find it
in the usual attached condition, with the lower half of the body
surrounded by a transparent tube of mucus. The Stentor has thus
moved away from the place where it was subjected to the mass of car-
mine particles, and has established itself in another situation.

fecuL% The behavior just described shows-clearly that the same individual

v

does not react always inthe same way to the same stimulus. The
stimulus and the other external conditions_remaining the same, the.
organism responds by a series of reactions becoming of more and
more pronounced character, until by one of them it rids itself of the
stimulation. Under the conditions described — when a dense cloud
of carmine is added to the water — the changes in the behavior may be
summed up as follows: —

(x) No reaction at first: the organism continues its normal activi-
ties for a short time.

(2) Then a slight reaction by turning into a new position, — a seem-
ing attempt to keep up the normal activities and yet get rid of the
stimulation.

(3) If this is unsuccessful, we have next a slight interruption of the
normal activities, in a momentary reversal of the ciliary current, tending

‘ to get rid of the source of stimulation.

[

- a

\|

MODIFIABILITY OF BEHAVIOR 177

(4) If the stimulus still persists, the animal breaks off its normal
activity completely by contracting strongly — devoting itself entirely,
as it were, to getting rid of the stimulation, though retaining the possi-
bility of resuming its normal activity in the same place at any moment.

(5) Finally, if all these reactions remain ineffective, the animal not
only gives up completely its usual activities, but puts in operation
another set, having a much more radical effect in separating the animal
from the stimulating agent. It abandons its tube, swims away, and
forms another one in a situation where the stimulus does not act upon it.

The behavior of Stentor under the conditions given is evidently a
special form of the method of the selection of certain conditions through

Soy reg me
ism “tries” one method of action;_i another, till one
succeeds.._Like other behavior based on this method, it is not a specific

reaction to any one stimulus, but is seen whenever analogous conditions
are produced in any way. Thus we may use in place of carmine other
substances. Chemicals of different kinds produce a similar series of
reactions. A decided change i in osmotic pressure has a somewhat
similar effect. There are variations in the details of the reaction series
under different conditions. Sometimes one step or another is omitted,
or the order of the different steps is varied. But it remains true that_
under conditions which gradually interfere with the normal activities —
of the e organism, the behavior consists in “trying” successively different
Teactions, till one is found that affords relief. The production of any
given n Step in the behavior cannot be explained as a necessary conse-

quence of the preceding step. On the contrary, the bringing into opera- /

tion of any given step depends upon the ineffectiveness of the sr ae

ones in getting rid of the stimulating condition. The series may_cease.
at any point, as soon as the stimulus disappears. Moreover, it is evi-

dent ce the succeeding steps are not mere accentuations of the pre-
ceding ones, but differ completely in character from them, being based

upon different methods of getting rid of the stimulation.

All our results on Stentor then show clearly that the sameorganism

may react to the same stimulus in various different ways. It may react
at first, then cease to react if the stimulus does not interfere with its
normal activities; it may react at first by a very pronounced reaction
(contraction), then later by a very slight reaction (bending over to one
side); or it may respond, if the stimulus does interfere with its normal
functions, by a whole series of different reactions, becoming of a more
and more pronounced character. Since in each of these.cases the ex-_
ternal conditions—remain. throughout the same, the change in_reaction
must be due to a change.in_theorganism. The organism which reacts

2 a

m | yi
varied activities, — a form which h The organ-

eh: oy

,

PD
17, a 5

SON

178 BEHAVIOR OF THE LOWER ORGANISMS

to the carmine grains by contracting.or-by_leaving its tube must be differ-
ent in some way from the organism which Lacie to the same stimulus
by bending to one side. No structural change is.evident, so that all
we can says. yis that the physiological state.oj the organism has changed. The
same organism in different physiological states reacts differently to the
same stimuli. It is evident that the anatomical structure of the organ-
ism and the different physical or chemical action of the stimulating |
agents are not sufficient to account for the reactions. Theva ‘he varying physio-
logical states of the animal are equally important factors. In Stentor
wé are compelled to assume at least five different physiological states to _
account for the five different reactions given under the same conditions.
We shall later find much occasion to realize the importance of physiologi-
cal states in determining behavior.

These relations may be stated from another point a view, which
leads to interesting questions. The present physiological state of an
organism depends upon its past history, so that we can say directly
that the behavior of such an organism as Stentor under given conditions
depends on its past history. This statement we know is markedly
true for higher organisms. What a higher animal does under certain
conditions depends upon its experience : — that is, upon its past history.
In the typical and most interesting case we say that the behavior of the
higher organism depends upon what it has learned by experience. Is
the change in the behavior of Stentor in accordance with its past history
a phenomenon in any wise similar in character to the learning of a higher
organism? In judging of this question we must rely, of course, entirely
upon objective evidence;— upon what can be actually observed.
When this is done, it is hard to discover any ground for making a dis-
tinction in principle between the two cases. The essential point seems
to be that after experience the organism reacts in a more effective way
than before. The change in reaction is regulatory, not merely hap-
hazard. And this. is as clearly the case in Stentor as in the higher
organism. It is true that, so far as we can see, the behavior of Stentor
shows in only a rudimentary way phenomena that become exceedingly
striking and complex i in higher organisms. Stentor seems to vary..its
behavior only in accordance.with.the experience that_either. (1) the
stimulus to which a strong reaction isat_first.given, doesnot really
interfere with its activities, so that reaction ceases ;or(2) thatthe reac-
tion already given is ineffective, since the interference with its activities
continues, so that another reaction is introduced.’ If the changes in

1 It is to be noted that nothing is said in this statement as to the Stentor’s perceiving

these relations. The statement attempts merely a formulation of the observed facts in
such a way as to bring out their relation to what we observe in higher organisms.

BEHAVIOR UNDER NATURAL CONDITIONS 179

the behavior of Stentor were not regulatory, becoming more fitted to the
existing conditions, a comparison with the behavior of higher animals
in learning would be out of place. But since the changes clearly are
regulatory, in the one case as in the other, it would be equally out of
place to deny their similarity, in this respect at least.

In another important feature the behavior of Stentor falls, so far as
our present evidence goes, far below the level of that found in the learn-

ing of higher animals. The modification in-the-behavior-induced—by
experience seems to. _last_but_a_very_shorttime, Immediately after

reacting in one way, which proves ineffective, it reacts in another. But
a short time after it apparently reacts in the same way as at first.* As _
a tule, it is evidently to the interest of an organism-living- under such Sim- _

ple conditions as Stentor to return to the first method of reaction when _
. again stimulated after a period of quiet, for as a rule this first method
is effective, and it would be most unfortunate for the Stentor to_proceed
to the extremity of abandoning its tube without a trial of simpler.
reactions. But the difference between behavior which is modified
only for a few moments after an experience, and that which is per-
manently modified, is undoubtedly important. The latter would never-
theless be developed from the former by a mere quantitative change,
so that the variation in duration does not constitute a difference in essen-
tial nature.

We may sum up the results of the present section as follows: The
same individual does not always behave in the same way under the same
external Conditions, but the behavior depends pon the physiological
condition of the animal. The reaction to any given stimulus is modified
by the past experience of the é animal, and the modifications are regula-
tory, not haphazard, in character. ‘The phenomena are thus similar
to those shown in the “learning” of higher organisms, save that the modi-
fications depend upon less complex relations and last a shorter time.

2. THE BEHAVIOR OF INFUSORIA UNDER NATURAL CONDITIONS

We have thus far dealt chiefly with the behavior of infusoria under
experimental conditions. In experiments the conditions are usually

1 This matter cannot be considered definitely settled. It is exceedingly difficult
in practice to devise and carry out experiments which shall actually determine the
length of time that the modified behavior lasts. A thorough, definitely planned investi-
gation should be directed precisely upon this point. Hodge and Aikins (1895) report
that Vorticella, which at first took yeast as food, later rejected the yeast, and that for
“several hours” it refused to take the yeast again. But unfortunately no further
details are given. We do not know whether the Vorticella was injured and took
no food at all, or what other conditions were present, so that we can build little upon
this observation.

180 BEHAVIOR OF THE LOWER ORGANISMS

made as simple as possible. All sources of stimulation save one are
excluded, in order that we may discover the precise effects of that one.
In our account of Paramecium we have seen that when more than one
source of stimulation is present, the behavior is determined by all the
existing conditions, so that often the behavior cannot be characterized as
a precise reaction to a definite stimulus. That this is true also for other
infusoria we have seen in a number of instances, particularly in our ac-
count of the contact reaction. It would be possible to add many other
examples to these, making a special chapter on “Reactions to Two or
More Stimuli,”’ but this would add no new principle to what we have
already brought out. The general statement may be made, that to
account for the way an infusorian behaves at a given time, it is as a rule
not sufficient to take into account a single source of stimulation, but all
the conditions must be considered.

We shall now look at certain features of the behavior of infusoria
under the conditions that are supplied by the environment, in all their
variety and complexity. We wish to see how the natural “wild” or-
ganism behaves. Our account cannot be exhaustive, for the natural
history of the thousands of species of infusoria remains largely to be
worked out. We shall merely examine certain typical features of the
behavior, devoting especial attention to the food reactions.

In our chapter on the “Action System’? we have seen some of the
chief variations in the natural behavior of infusoria. We have there seen
that the infusoria can be divided, according to their methods of life, into
three main groups: those that are attached, those that creep over sur-
faces, and those that swim freely. ‘The behavior in these different groups
necessarily differs much. Yet, as we have seen, every possible gradation
exists from one group to another, and even the same individual may at
different periods represent each different group. The behavior is sim-
plest and least varied in the free-swimming organisms; more varied in
those which habitually creep along a surface; most complex in those
which live attached. The reason for this seems to be as follows: In
the open water the conditions are exceedingly simple. The free-swim-
ming organism may escape an injurious stimulus simply by swimming
away. In the fixed organism, on the other hand, the conditions are more
complex. At any moment both the solid and the free fluid are acting
on the organism. For a fixed animal to obtain food and escape injurious
conditions, varied devices are necessary. It cannot at once solve any
difficulty by departing, as the free organism can. We find, then, that
such fixed organisms have developed varied reaction methods (see the
preceding chapter).

There is much variation in the complexity of behavior even among

BEHAVIOR UNDER NATURAL CONDITIONS 181

species living under similar conditions. Some of the free-swimming
species are very supple, changing form continually. Such is the case,
for example, with Lacrymaria olor, which stretches its long neck in
every direction, shortens it until it has almost disappeared, reéxtends it,
-and seems to explore thoroughly the surrounding region. Such an
organism has, of course, much better opportunity for effective behavior
by the method of trial than has such a rigid form as Paramecium.

Similar differences are found among the creeping infusoria, and
among the fixed species. Some fixed infusoria contract frequently,
while others contract only rarely. In some cases the contraction occurs
at regular intervals, even when there is no indication of an external
stimulus. This is the case with Vorticella. There is no evidence that
in infusoria periods of rest, comparable with the sleep of higher animals,
are alternated with periods of activity. Hodge and Aikins (1895)
kept a single Vorticella continuously under observation for twenty-one
hours, besides intermittent study for a number of days. They found
that there was no period of inactivity. During five days the cilia were
in continuous motion, food was continuously taken, and contractions
were repeated at brief intervals.

A number of fixed infusoria live, like Stentor reselii, in tubes, some
gelatinous, some membranous in character. As a rule these tubes are
formed in a very simple manner. The material of which they are com-
posed is secreted by the outer surface of the animal. In the repeated
contractions and extensions of the body this material is worked off, in
the form of a sheath. The tube may become thicker by the secretion
of more material on the surface of the animal. It often grows in length,
either as the animal becomes longer or as it migrates farther out toward
the open end of the tube. In the secreted material, which is often trans-
parent, all sorts of foreign substances may become embedded, in the
following way: They are carried as particles to the oral disk by the cilia.
Thence they pass backward over the surface of the body, till they reach
the gelatinous substance of the tube, where they become embedded.
Thus in most cases the formation of the tube seems a direct consequence
of the secretion of the mucus-like substance over the body of the animal,
taken in connection with the usual movements. The intervention of any
special type of behavior directed toward the end of forming the tube
seems unnecessary. But in some cases, as we have seen in our account
of Stentor, the tube is formed at the beginning by a definite set of move-
ments, of a character especially fitted to produce such a structure. For
details as to different kinds of tubes, and their structure and method
of formation, reference may be made to Biitschli’s great work on the
infusoria (1889).

182 BEHAVIOR OF THE LOWER ORGANISMS

A set of phenomena that is deserving of careful study for its implica-
tions as to the nature of behavior is that involved in the activities pre-
liminary to conjugation. It is possible that the organisms are in a
modified physiological condition at this time, behaving differently from
usual. Critical observations on this subject, of such a nature that we
can use them for our present purpose, are too few in number to make
possible a unified account of these phenomena. An account of the
facts for Paramecium is givenon page 102. The field is one deserving
of much further work.

3. Foop Hasirs

The food habits of the infusoria are among the most interesting of
their activities to the student of animal behavior. As to their food habits,
we can with Maupas (1889) divide the infusoria into two classes. The
first includes those that bring the food to the mouth by means of a
vortex produced by the peristomal cilia; the second those that go about
in search of food, seizing upon it with the mouth, like a beast of prey.
The former live chiefly upon minute objects, the latter upon larger or-
ganisms. There is, of course, no sharp distinction between the two
classes. Most of the infusoria with strong vortices move about more or
less in search of food, and most of those that seize upon their prey after
a search are aided by a more or less pronounced vortex. Thus the
roving or searching movements and the vortex are factors common
to the food habits of most of the infusoria. The positive contact re-
action further plays a most important part in obtaining food.

Those species that depend primarily upon the ciliary vortex for
obtaining food usually feed upon bacteria and other minute organisms
and upon finely divided organic matter, — bits of decaying plant or
animal material. Of this class of organisms Paramecium and Stentor
are types. In some, as in Paramecium, the food is limited to most
minute bodies, such as bacteria and small alge. Stentor and others
may take larger objects. Other infusoria and even rotifers of a con-
siderable size are often seen embedded in the internal protoplasm of
Stentor. Such animals are caught in the strong ciliary vortex, carried
to the buccal pouch, which often contracts in such a way as to prevent
their escape, and are then taken through the mouth into the internal
protoplasm.

How do these organisms succeed in getting the food that is fitted for
them? Is there a selection of food, and how is it brought about? Much
of the difficulty as to the selection of food is solved by the conditions
under which these animals usually live. They are found as a rule in

BEHAVIOR UNDER NATURAL CONDITIONS | 183

water which contains decaying vegetable or animal matter, and therefore
swarms with bacteria. Hence the usually ciliary current brings food
continuously, and little selection is necessary. The animals take,
within wide limits, all that the ciliary current brings. Bits of scot,
India ink, carmine or indigo, chalk.granules, and the like are swallowed
along with the bacteria, though of course they are useless as food. They
are merely passed through the body and ejected along with the indi-
gestible remains of the food. They do no harm, and the animal may
continue to take them indefinitely, provided it receives in addition a suffi-
cient amount of real food. If the ciliary currents do not bring food,
of course the organisms die after a time. It is well known that infusoria
appear suddenly in immense numbers, or disappear with equal rapidity,
according as the conditions are favorable or unfavorable.

But the animals do determine for themselves, to a certain extent,

‘what things they shall take as food, and what they shall not. This is
not done, so far as can be observed, by a sorting over of the food by the
cilia, as the water current cgrries it to the mouth. It is true that not .
all the particles in the vortex produced by the cilia pass into the mouth.
But this is due to the simple mechanical conditions. The vortex is
very extensive, and the mouth is very small, so that only a fraction of the
water in the vortex can ever reach the mouth. Hence inevitably a
large share of the particles in the vortex are whirled away. But this is
true of particles which are valuable for food as well as of those which are
not. If Stentor is placed in water containing immense numbers of small
algal cells which are useful as food, it is found that as many of these pass
through the vortex without being taken as happens in the case of worthless
particles of soot or carmine.

Choice of food occurs in a somewhat cruder fashion than through a
sorting of the individual particles by the cilia. It takes place through
the reaction with which we have become familiar in studying the behavior
of the organisms under various stimuli. Thus in Paramecium the re-
jection of unsuitable food takes place through the avoiding reaction. If
the ciliary current brings water containing various chemicals in solution,
or if large solid objects are brought to the mouth, or too great a mass
of smaller particles, the Paramecium shifts its position in the usual way.
It backs more or less, turns toward the aboral side, and moves to another
place. The avoiding reaction is in itself always an expression of choice,
in so far as it determines the rejection of certain conditions of existence.
In Stentor and Vorticella choice of food occurs in a similar manner,
though in these fixed infusoria there is, as we have seen, usually more
than one way of rejecting unsuitable conditions.

In Stentor the following behavior is at times observed. The animal

184 "BEHAVIOR OF THE LOWER ORGANISMS

is outstretched and feeding quietly in the usual way. Many small
objects pass into the buccal pouch and are ingested. Suddenly a larger,
hard-armored infusorian, Coleps, is drawn into the pouch. At once
the ciliary current is reversed and the Coleps is driven out again. Then
the current is resumed in the usual direction. Vorticella and other fixed
infusoria often reject large objects in the same way. But besides re-
versing the ciliary current, these organisms may, when the ciliary current
brings unsuitable material, bend over into a new position, contract,
or leave their place of attachment and swim away. All these reactions
have been described in detail in our account of the behavior of Stentor.

Thus the choice of food in all these organisms depends merely upon
whether the usual negative or avoiding reactions are or are not given.
The avoiding reaction is the expression of such choice as occurs. Look-
ing at the matter from this standpoint, we are forced to conclude that the
entire behavior involves choice in almost every detail. The animals,
as we have seen, are giving the avoiding reaction in a certain degree,
from a slight widening of the spiral course to the powerful backward
swimming, almost continuously. The straightforward course is the
expression of positive choice or acceptance; the avoiding reacting of
negative choice or rejection. No distinction can be made between choice
and the usual behavior. Indeed, choice is the essential principle of
behavior based on the method of trial.

What happens if the organisms settle down and attach themselves
in a region where no food exists? This question seems not to have been
specially investigated. But it is known that under most kinds of un-
favorable conditions, — conditions which interfere with the normal
functions, — the animal, after a time, leaves its place and swims away
to a new location. Doubtless this happens also when food is lacking.

We may sum up the food habits of this first class of ciliates as fol-
lows: They settle down in a certain region and then bring a current
of water to the mouth. The particles in this current are taken as food,
without any sorting, so that many that are not useful are ingested along
with the others. But if decidedly unsuitable material is brought, then
the animal reacts as to other unfavorable stimuli — reversing the cur-
rent, contracting, shifting position, or finally moving away to a new place.
The method of trial of varied movements is at the basis of the behavior
here as elsewhere.

The second class of ciliates includes those which move about in search
of their food, preying upon larger organisms and seizing them with the
mouth. Maupas has well called these the hunter ciliates. The method
of taking food in these animals often resembles in many respects that of
the species already described. Thus Stylonychia runs about here and

BEHAVIOR UNDER NATURAL CONDITIONS 185

there, producing a strong vortex leading to its mouth. This often carries
other infusoria, of considerable size, to the mouth. These are then
seized and worked gradually back into the internal protoplasm. Some
species move about more rapidly and more extensively, while the ciliary
vortex is reduced so that it is of little consequence for food getting. On
coming in contact with another infusorian the latter is seized by the
usually armored mouth; this is opened widely and the prey is swallowed.
In this way such infusoria often feed upon other animals almost or quite
as large as themselves, the mouth opening widely and the body becoming
greatly distended.

An excellent example of one of these hunter ciliates is furnished by
Didinium. This animal (Fig. 113) is cask-shaped, with a truncate
anterior end, bearing in its centre the mouth on
a slight elevation. The body bears but two
circles of cilia. By the aid of these, Didinium
swims about rapidly, revolving to the right on
its long axis and frequently changing its direc-
tion. On coming in contact with a solid object
it stops, pushes forward against the object the
conical projection which bears the mouth, and Aa ee

° = : Fic. 113. — Didinium seiz-
revolves rapidly on its long axis. The mouth jing Paramecium. After Bal-
is armed with a number of strong ribs ending biani.
in points, which apparently project a little from the cone bearing the
mouth. When pushed forward against a soft organism, these points
apparently pierce and hold it. The revolution on the long axis has the
appearance of a process of boring into the body. ‘The mouth now opens
widely and swallows the prey. Paramecium often falls a victim to
Didinium in this way (Fig. 113). Sometimes the Didinium is smaller
than its prey, forming after the feeding process a mere sac over its
surface.

The point which interests us at present is that Didinium reacts in
the way described not merely to objects which may serve as food, but
also to all sorts of solid bodies. In other words, the process is one of the
trial of all sorts of conditions. On coming in contact with a solid,
Didinium “tries” to pierce and swallow it. If this succeeds, well and
good; if it does not, something else is “tried.”’ In a culture containing
many specimens of Didinium, the author has seen dozens of individuals
reacting in this way to the bottom and sides of the glass vessel, apparently
making persevering efforts to pierce the glass. Others “try” water
plants, or masses of small algz, about which many specimens gather at
times. Of course they get no food in this way. On coming in contact
with each other, the animals react in the same way, often becoming

186 BEHAVIOR OF THE LOWER ORGANISMS

attached to each other, and sometimes forming chains of four or five.
But they never succeed in swallowing one another. They often try
rotifers in the same way, but the outer integument of these organisms
is so tough that Didinium does not succeed in piercing it, and the rotifer
escapes. Stentor and Spirostomum are often fastened upon, but usually
escape, owing to their large.size, great activity, and rather tough outer
covering. The reason why Paramecium is usually employed as food
rather than other organisms is clearly due to the fact that when the
Didinia try these, they usually succeed in piercing and swallowing them,
while with most other objects they fail.’

Didinium is a type of the hunter ciliates in this respect. The process
of food-getting is throughout these species one of trial of all sorts of things.
There is no evidence that in some unknown way the infusoria perceive
their prey at a distance, nor that they decide beforehand to attack certain
objects and leave others unattacked. They simply “prove all things
and hold fast to that which is good.”

We cannot do better in emphasizing this point than to quote a por-
tion of the words of the veteran investigator Maupas, as given in Binet’s
“The Psychic Life of Micro-Organisms” (pp. 48, 49):—

“These hunter infusoria are constantly running about in search of
prey; but this constant pursuit is not directed toward any one object
more than another. They move rapidly hither and thither, changing
their direction every moment, with the part of the body bearing the bat-
tery of trichocysts held in advance. When chance has brought them in
contact with a victim, they let fly their darts? and crush it; at this point
of the action they go through certain manceuvres that are prompted
by a guiding will. It very seldom happens that the shattered victim
remains motionless after direct collision with the mouth of its assailant.
The hunter, accordingly, slowly makes his way about the scene of action,
turning both right and left in search of his lifeless prey. This search
lasts a minute at the most, after which, if not successful in finding his
victim, he starts off once more to the chase and resumes his irregular
and roving course. These hunters have, in my opinion, no sensory
organ whereby they are enabled to determine the presence of prey at a
distance; it is only by unceasing and untiring peregrinations both day

? Balbiani (1873) described Didinium as discharging trichocysts from the mouth
region against its prey, thus bringing it down from a distance. This account has not
been confirmed by other observers, and the writer has never seen anything of the sort in
the innumerable cases of food-taking in Didinium which he has observed. It can hardly
be doubted that the trichocysts represented in Balbiani’s figure (our Fig. 113) really come
from the injured Paramecium, and not from the Didinium.

? This use of the trichocysts has not been confirmed by other writers and was not
absolutely observed by Maupas himself.

BEHAVIOR UNDER NATURAL CONDITIONS 187

and night that they succeed in providing themselves with sustenance.
When prey abounds, the collisions are frequent, their quest profitable,
and sustenance easy; when scarce, the encounters are correspondingly
less frequent, the animal fasts and keeps his Lent. The Lagynus
crassicollis, accordingly, never sees its victim from a distance and in no
case directs its movements more toward one object of prey than toward
another. It roams about at random, now to the right and now to the
left, impelled merely by its predatory instinct — an instinct developed
by its peculiar organic construction, which dooms it to this incessant
vagrancy to satisfy the requirements of alimentation.”’

It is evident that these words of Maupas are an excellent description
of behavior based on the general method of trial of all sorts of conditions
though varied movements, and they bring out clearly the essential prin-
ciples in the food reactions of infusoria. 'The same method of behavior
is found, as we have seen, throughout almost the whole circle of activi-
ties in these organisms; the food reactions epitomize the entire behavior.

LITERATURE X

A. Modifiability of behavior in infusoria: JENNINGS, 1902, 1904 d; HODGE AND
AIKINS, 1895.
&. Food habits of infusoria: MAUPAS, in Binet, 1889; BALBIANI, 1873.

PART II

BEHAVIOR OF THE LOWER METAZOA

CHAPTER XI
INTRODUCTION AND BEHAVIOR OF CCELENTERATA

INTRODUCTION

W8HILE unicellular forms are the very lowest organisms, an account
limited to their behavior alone might give us a one-sided view of the prin-
ciples of behavior in the lower organisms. The Metazoa differ from the
Protozoa structurally in the important facts that their bodies are made
of many cells and that they have a nervous system. Does the behavior
of such organisms differ essentially from that of the Protozoa? Have
we been dealing in our study of unicellular organisms with a peculiar
group, whose behavior is of a character essentially different from that
of other animals? How far do the general principles to be deduced from
the behavior of Protozoa hold for animals in general? To answer these
questions is the province of the following chapters.

We shall take up in detail the behavior of only one of the lowest
groups of Metazoa — the ccelenterates. This will be followed by a
chapter on some of the main features of behavior in other invertebrates.
A general analysis of behavior in both Protozoa and the lower Metazoa
is found in the third part of the book.

BEHAVIOR OF CCELENTERATA

The Ccelenterata or Cnidaria form, perhaps, the lowest of the larger
groups of Metazoa. This group includes the fresh-water Hydra,
hydroids, sea anemones, corals, and jellyfishes or meduse. The
behavior of the corals and of hydroids has been comparatively little
studied, so that the present account will be limited mainly to Hydra, the
sea anemones, and meduse.

All of these animals are made up of many cells, of many different
kinds, and usually arranged in three more or less irregular layers. Of

. 188

BEHAVIOR OF CELENTERATA 189

special interest from the standpoint of behavior are the nerve cells. In
Hydra these consist of comparatively few, small cells with long, branched
processes, scattered among the ectoderm and entoderm cells. They
apparently serve to connect the other cells. In the sea anemones the
nerve cells are more numerous than in Hydra, but are likewise scattered
throughout the body, in both ectoderm and entoderm. They are some-
what more numerous in the neighborhood of the mouth than elsewhere.
In Meduse the nervous system is more concentrated. The cells and
fibres form two rings about the edge of the body: one lies just beneath
the ectoderm of the exumbrella, the other beneath that of the subum-
brella. These rings are interconnected by scattered fibres. A plexus
of nerve fibres covers the entire concave surface of the subumbrella
and manubrium, beneath the ectoderm. ‘This plexus is compared by
Romanes as regards texture to a sheet of muslin. Nerve cells and fibres
are found also in the tentacles; but are not known on the convex surface
of the exumbrella. The two marginal nerve rings are often spoken of
as the “central nervous system” in meduse.

1. ACTION SYSTEM. SPONTANEOUS ACTIVITIES

In the ccelenterates we take up animals with action systems differing
much from those of the organisms we have hitherto studied. The chief
movements are due to contractions and extensions of parts of the body
and tentacles, produced by contractions of the muscle fibres. The body
is flexible, and being radially symmetrical may contract or bend with
equal ease in any direction.

Under natural conditions, Hydra and the sea anemone are usually
attached and at rest, while the medusa may be in movement. Let us ex-
amine the behavior under such conditions, when no observable stimulus
is acting on them, aside from the usual conditions of existence.

If we observe an undisturbed green Hydra attached to a water plant
or the side of a glass vessel, we find that it usually does not remain still,
but keeps up a sort of rhythmic activity. After remaining in a certain
position for a short time it contracts, then bends to a new position, and
reéxtends (Fig. 114). In this new position it remains for one or two
minutes, then it again contracts, changes its position, and again extends.
This continues, the changes of position occurring every one or two min-
utes. In this way the animal thoroughly explores the region about its
place of attachment and largely increases its chances of obtaining food.
This motion seems to take place more frequently in hungry individuals,
while in well-fed specimens it may not occur.

Thus contractions take place without any present outward stimulus;

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190 BEHAVIOR OF THE LOWER ORGANISMS

the movements are due to internal changes of some sort, like those of
Vorticella. ‘The same behavior may be produced, as we shall see later,
by external stimuli.
In the yellow Hy-
dra such move-
ments do not occur
—at least not with
such frequency.

Fic. 3115. — Dia-
gram of different posi-

Fic. 114. — Spontaneous changes of positions in an undis- tions taken by Hydra, as
turbed Hydra. Side view. The extended animal (1) contracts seen from above. After
(2), bends to a new position (3), and then extends (4). Wagner.

This is apparently correlated with the fact that the yellow Hydra has

very long tentacles, which lie in coils all about it, so that exploratory

movements are not necessary in order to reach such food as may be
found in the neighborhood.

If a green Hydra is left for long
periods undisturbed, it does not
remain attached in the same posi-
tion, but moves about from place
to place. The movements often
take place in random directions, —
the animal starting first in one direc-
tion, then in another. Figure 116
shows the movements of a green
Hydra, which was left alone for some
days in the bottom of ‘a large, clean
glass dish, the light coming from a

' window at the right. This move-
ment is probably brought about by
Fic. 116.— Path followed by a green hunger — the animals taking a new
Hydra that was left for some days undisturbed position when food becomes scarce.

on the bottom of a clean glass dish. After .
Wagner (1905). s Hydra may move about in several

BEHAVIOR OF CG@LENTERATA I9l

different ways. In the commonest method the animal places its free
end against the substratum, releases its foot, draws the latter forward,
reattaches it, and repeats the process, thus looping along like a measur-
ing worm (Fig. 117). In other cases it attaches itself by its ten-
tacles, releases its foot, and 1

uses the tentacles like legs.
A still different form of loco-
motion has been described,
in which the animal is said
to glide along on its foot;
how this is brought about is
not known.

In sea anemones, rhyth-
mical contractions of the un-
disturbed animal have ap-
parently not been described.
But Loeb (1891, p. 59) finds
that Cerianthus if not fed
will after a time leave its
place in the sand and creep
about, finally establishing
itself in a new place. The
common sea anemone Me-
tridium moves about fre-
quently from place to place
on the sides or bottom of the
aquarium, and so far as can
be observed, this seems often
due simply to hunger or other
internal conditions; it Occurs af,
under apparently uniform
external conditions. A common method of movement in sea anemones
is to glide about on the foot, — the lower surface of the foot sending
out extensions and moving in a manner similar to that of the foot of
mollusks. There are doubtless other methods of locomotion.

The spontaneous contraction and change of position which plays a
subordinate part in fixed forms has become the rule in meduse. They
are commonly found swimming about ‘by mearis of rhythmical contrac-
tions. Since there are no corresponding changes in external condi-
tions, these contractions must be due to internal changes. The
internal changes need not of course be themselves of a rhythmical
character. They may take place steadily, inducing a contraction only

i
"

———
_——

Fic. 117.— Hydra looping along like a leech.
er Wagner (1905). 1-6, Successive positions.

192 BEHAVIOR OF THE LOWER ORGANISMS

when a result of a certain intensity has been reached (see Loeb, 1900,
p- 21).

In the small medusa Gonionemus there is under natural conditions a
cycle of activity that is of great interest; it has been well described by
Yerkes (1902, a and b, 1903, 1904) and Perkins (1903). At times the
animal is found attached by certain adhesive pads on its tentacles to

Fic. 118. — Young Gonionemus resting on the bottom, with the opening of the bell upward.
After Perkins (1903).
the vegetation of the bottom or to other surfaces (Fig. 118). Leaving
its attachment, it swims upward to the upper surface of the water, the
convex surface of the bell being upward, and the tentacles contracted
(Fig. 119). Reaching the upper surface it turns over
“and floats downward with bell relaxed and inverted,
and tentacles extending far out horizontally in a wide
snare of stinging threads which carries certain destruc-
tion to creatures even larger than the jellyfish itself
(Fig. 120)” (Perkins, 1903, p. 753). Reaching the

Fic. 119. — bottom, it swims again to the top and repeats the
oa anaant “with Process. It may thus continue this process of “ fish-
contracted tentacles. ing,”’ as Perkins calls it, all day long. It is chiefly in
After Perkins (1993). this way that it captures its food.

This cycle of spontaneous activities is in some respects similar to
that of the green Hydra described above, though much more complex.
Both illustrate the fact that complex movements and changes of move-
ment may occur from internal causes, without any change in the environ-
ment.

2. CONDITIONS REQUIRED FOR RETAINING A GIVEN POSITION;
RIGHTING REACTIONS, ETC.

Hydra and the sea anemones tend to retain a certain position; we
usually find them at rest with foot attached and head free. This usual
position is often said to be due to a reaction to gravity or to contact, or

BEHAVIOR OF CG@LENTERATA 193

to some other simple stimulus. It will be found instructive to examine
the different conditions on which depends whether the animal shall or
shall not retain a given position in which it finds itself. It will be found
that the matter is not an entirely
simple one.

Let us take first the case of Hydra.
Suppose the animal to be placed on a
horizontal surface with head down-
ward and foot upward. It does not.
retain this position, but bends the
body, placing the foot against the
bottom, releases its head, and
straightens upward. This is what
is commonly called the “righting”
reaction. In Hydra it is not due to
a tendency to keep the body in a cer-
tain position with reference to gravity,
for the animal may remain attached
to the bottom, with head projecting
upward, or to the surface film, with
head projecting downward, or to a
perpendicular surface, with the body
transverse or oblique to the direction
of gravity. There is even apparently
a certain tendency to direct the head
downward. Thus out of 100 green
Hydras attached to a perpendicular
surface, 96 had the head lower than
the foot, 3 were horizontal, and 1 had
the head directed upward. It is thus
clear that the righting reaction of a
Hydra which has been inverted on
the bottom cannot be due to any
unusual relation to the direction of
gravity.

To what, then, is the reaction
due? Evidently there is a tendency to
keep the foot in contact with a surface, for the body is bent till the foot
comes in contact. But this is not all; the reaction does not stop at this
point. There is likewise a tendency to keep the head free, for it is re-
leased. But still this is not all, for now the body is straightened; then
the tentacles are spread out symmetrically in various directions.

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194 BEHAVIOR OF THE LOWER ORGANISMS

It is clear that the reaction is directed toward getting the organism
into its usual position, which might perhaps be called the “normal” one;
this normal position has various factors, — attachment of foot, freedom
of head, comparative straightness of the body, and tentacles outspread.
This is, of course, exactly the
position which is most favorable
for obtaining food.

Suppose now that our Hydra
has reached this position, and
all the conditions remain con-
stant; is this sufficient? We
find that it is not. If the con-
ditions remain so constant that
no food is obtained, the Hydra
becomes restless and changes the
position of its body repeatedly,
though still retaining its attach-
ment by the foot. But later
even this is given up, and the
animal, of its own internal im-
pulse, quite reverses the position
attained through the “righting
reaction.” It now bends its
body, attaches its head, and re-
leases its foot, thus bringing it
back into the inverted position.
¢ Is this because the irritability

Fic. 121. — Process by which Cerianthus rights of head and foot have become
itself when inverted in atube. The figuresaretaken reversed, so that the head now
fied eee oe er After sands to remain attached, the

foot free? Apparently not, for
no sooner has the organism taken the inverted position than it draws
its foot forward and now performs the “righting reaction” again, so that
it stands once more on its foot. These alternations of behavior are
repeated, and we find that by this means the animal is moving from
place to place, as in Fig. 117.

It seems clearly impossible to refer each of these acts or the whole
behavior to any particular present external stimulus. Through hunger
the Hydra is driven to move to another region, and these different oppo-
site acts are the means by which another region is reached. Each step
in the behavior is partly determined by the preceding step, partly by
the general condition of hunger. The same behavior is often seen, as

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BEHAVIOR OF C@LENTERATA . 195

we shall see later, under continued injurious stimulation of different
kinds.

In speaking of righting reactions, it is often said that the organism
is forced by the different irrita-
bilities of diverse parts of the
body to take a certain orienta-
tion with reference to gravity
or to the surface of contact
(see, for example, Loeb, 1900,
p- 184). The facts just y vil )
brought out show that we can ANAT
in Hydra consider this orienta-
tion forced only in the general !
sense that all things which
occur may be _ considered
forced. Man takes sometimes (===>
a sitting position, sometimes a _Fyg. 122. — Position taken by Cerianthus after it
standing one, sometimes a re- has been placed on its side on a wire mesh. After Loeb
clining one, depending upon “*%””
his “physiological state” and past history, and the facts are quite
parallel for Hydra. So far as objective evidence shows, the behavior is
not forced in Hydra in any other sense than it is in man. The animal
takes that position which seems best adapted to
the requirements of its physiological processes;
these requirements vary from time to time.

YO In the sea anemone Cerianthus the conditions
<xo for retaining a certain position are somewhat more
Bross complex than in Hydra, according to the account
©: given by Loeb (1891). The animal is usually
_ Fic. 123.—Cerianthus found in an upright position, occupying a mucus-,
rincchaotle ne a ncault e lined tube in the sand. If placed head down-
nage S Gben the latter. ward in a test-tube, it rights itself in the same
} way as Hydra, freeing the head, bringing the
foot into contact, and straightening the body (Fig. 121). But in this
animal, gravity clearly plays a part in the behavior. Loeb placed the
animal on its side on a wire screen of large mesh. Thereupon it bends
its foot down through the meshes, lifts up its head, and takes its usual
position in line with gravity (Fig. 122). If now the screen is turned
over, the animal again directs its head upward, its foot downward — as
a human being under similar circumstances would do if possible. It
may thus weave itself in and out through the meshes (Fig. 123).
But to be in line with gravity, with head free, is not the only require-

196 BEHAVIOR OF THE LOWER ORGANISMS

ment for Cerianthus. Loeb found that it would not remain indefinitely
in this position on the wire screen, as it does in the sand. After a day or
so it pulls its foot out of the wire and seeks a new abode. Only when it
can get the surface of its body in contact with something, as is the case
when it is embedded in the sand in its natural habitat, is it at rest. If
this condition is fulfilled, the requirement of the usual position in line
with gravity may be neglected. Loeb found that when the animal is
placed in a test-tube, so that its body is in contact with the sides, it re-
mains here indefinitely, even though the tube is placed in a horizontal
position (Loeb, 1891, p. 54). The head is bent upward, but the body
remains transverse to the direction of gravity. Similarly, the anemone
Sagartia may ofttimes take a position on the surface film with head
down, although usually it maintains an upright position (Torrey, 1904).

But even the usual position in line with gravity, and with sides in
contact, does not satisfy Cerianthus indefinitely, if left quite undisturbed.
If it secures no food, it again leaves its place and seeks another region.

Thus that the animal may remain quiet in a given position a consid-
erable number of conditions should be fulfilled, constituting altogether
what we may call the “‘normal”’ state of the animal. The conditions are
the following: (1) the foot should be in contact; (2) the head should
be free; (3) the body should be straight; (4) the axis of the body should
be in line with gravity, with the head above; (5) the general body sur-
face should be in contact; (6) food should be received at intervals.

If these conditions are largely unfulfilled, the animal becomes rest-
less, moves about, and finds a new position. But no one of these condi-
tions is an absolute requirement at all times, unless it be that of having
the head free. In the wire screen (Fig. 122) the animal remains for a
day or so if in the required position with reference to gravity, even
though foot and body surface are not in contact. In the horizontal test-
tube it remains with foot and surface in contact, though the body is not
straight nor in line with gravity. If all conditions are fulfilled save that
of food, the animal remains for a time, then finally moves away.

Clearly, the holding of any given position depends, not on the rela-
tion of the body to any one or two sources of stimulation, but on the
proper maintenance of the natural physiological processes of the organ-
ism. The animal does not always maintain a certain position with rela-
tion to gravity, nor does it always keep its body straight, nor its foot in
contact, nor its body surface in contact. It does not at all times receive
food. It may remain for considerable periods with one or more condi-
tions lacking. It tends on the whole to take such a position as is most
favorable to the unimpeded course of the normal physiological processes.
Certain usually required conditions may be dispensed with, provided

BEHAVIOR OF C@:LENTERATA 197

other favorable ones are present. The behavior represents a compro-
mise of the various needs imposed upon the animal by its physiological
processes.

In the sea anemone Antholoba reticulata, according to Biirger (1903),
the requirements for retaining a given position are extraordinary. This
animal is usually found attached to the backs of crabs; it is thus carried
about, and finds much opportunity for obtaining nourishment. If re-
moved from the crab’s back, the animals attach themselves to the stony
bottom and spread the tentacles. But after four or five days they re-
lease their hold on the bottom and invert themselves, directing the foot
upward. Now when a crab’s limb comes in contact with the foot, the
latter attaches itself and folds about the limb, so that the anemone is
dragged about by the crab. It now, in the course of several hours,
climbs up the crab’s leg to its back, where it establishes itself. The sea
anemone thus by its own activity attains the extraordinary situation
where it is usually found. The whole train of action is like that shown
in the complicated and adaptive instincts of higher animals.

3. GENERAL REACTION TO INTENSE STIMULI

The most characteristic reaction of the coelenterates to intense stimuli
of all sorts is a contraction of the whole body. In Hydra and the sea
anemones the body is thus shortened and thickened, becoming more
nearly spherical. The animals thus ‘shrink close to the substratum
and present less surface than before to the stimulating agent. In the
meduse the sudden contraction of course carries the animal away from
the stimulating object. The first contraction is usually repeated many
times, thus inaugurating a period of swimming by which the animal may
be widely removed from the stimulus. Such contractions occur in re-
sponse both to general stimulation and to local stimulation, if the latter
is very intense.

Under most circumstances the contraction of Hydra or the sea anem-
one of course tends to remove the organism from any source of danger,
rendering it for example less likely to be seized by a predatory animal.
But the reaction takes place in the same way under circumstances in
which it is of no defensive value. If the foot of the attached Hydra
is strongly stimulated, the animal contracts as usual; the contraction is
then of course /oward the source of stimulation, not away from it. If
the entire vessel containing the animals is heated to 30 degrees, the
Hydras contract, though this of course does not tend to remove them
from the high temperature. It is clear that for all sorts of stimuli that
are unfavorable these animals have a certain reaction which is usually

a.

a

198 © BEHAVIOR OF THE LOWER ORGANISMS

regulatory (beneficial); they give this reaction whatever the nature of
the unfavorable stimulus, even under circumstances where it is not
regulatory. This is an illustration of a characteristic general trait of
behavior in lower animals; their reactions are commonly not specific,
but general in character. As we shall see later, this contraction is not
the final recourse of the stimulated ccelenterate. If stimulation con-
tinues, the animal usually sets in operation other activities, which remove
it from the stimulating agent.

4. LOCALIZED REACTIONS

Hydra. —In Hydra, intense stimuli restricted to a small spot on
the body or a tentacle usually produce contraction at that point, some-
times spreading much or
little, sometimes not at all.
This reaction is produced by
many sorts of stimuli. If
the contraction remains pre-
cisely localized, as it some-
times does, the body or
tentacle bends sharply at
the point stimulated.

A precisely _ localized
chemical stimulus is pro-
duced in the following way.

Fic. 124.— A chemical (ch.) is brought against a A fine capillary glas . rod =
certain spot on one side of a Hydra (a). Thereupon dampened and its uip is
this spot contracts, bending the Hydra toward the side dipped in some powdered

parepraata chemical. Methylene blue
or methyl green is convenient to use, since the distribution of the chemi-
cal in the water is easily seen by means of the color. The point of this
fine rod, covered with the chemical, is brought close to the body of a
Hydra. The chemical diffuses and reaches a small area on the body.
Local stimulation by heat may be produced with the simple apparatus
devised by Mast (1903). A glass tube is drawn out at its middle to
capillary size, then bent so as to form a loop. The two ends are
passed through a cork for support, and to them are attached rubber
tubes. In this way water of any desired temperature may be passed
through the fine tube, and this may be brought close against the body of
the animal at any desired point.

_ When the strong chemical or the heat reaches a certain spot on the
body, this spot at once contracts, so that the body makes a knee-shaped

BEHAVIOR OF CG@LENTERATA . 99

bend at this point (Fig. 124). Such a bending is produced by most
strong chemicals; strong acids placed in a capillary tube, the tip of
which is applied to the body, show it clearly. As a result of the bend
the head of the animal becomes directed toward the chemical or the
heated region, and is therefore strongly stimulated, so that the Hydra
now contracts as a whole. Thus the result of the bending is to carry
the most sensitive part of the animal into the injurious agent, where it
is still further injured. This reaction is produced only by strong, inju-
rious agents, and is really an incidental result of the local injury pro-
duced. The point injured remains contracted for a long time after the
stimulating agent has ceased to act. The Hydra may contract com-
pletely, so that the bend disappears, but on extension the bend is still
found at the injured spot. It is evident that this bending reaction is
not a regulatory one, and it is apparently never shown in nature, since
the conditions necessary for its production are practically never present.
It is a product of the laboratory. As we shall see later, after reaction
in this manner, Hydra usually sets in operation other reactions, which
do act in a regulatory way.

Sea Anemones. — Intense local stimulation of the column in the sea
anemones usually produces a contraction of the entire body, or a move-
ment of tentacles on the side stimulated, in the way described later. In
Sagartia (Torrey, 1904, p. 208), stimulation of the edge of the foot
induces a local contraction of the foot and base of the column, with
discharge of acontia — the defensive weapons of the animal.

Local stimulation of the tentacles causes in the different sea anem-
ones various reactions. Often slight local stimulation causes the tenta-
cles to wave about; this and similar phenomena will be described in
connection with the food reactions. In most sea anemones local stimu-
lation of the tentacles, especially if intense, causes them to shorten by con-
traction, or to collapse and become very slender. This is followed in
many cases by a contraction of the whole body. In Aiptasia an immedi-
ate contraction of the entire body follows even a slight stimulation of
the tip of one of the long tentacles.

Meduse. —In medusze, intense stimulation of one side of the bell
causes immediate contraction of that side, accompanied by a less marked
contraction of the remainder of the bell. The stronger contraction on
the side stimulated turns the animal away from that side, and its subse-
quent locomotion removes it at once from the stimulating agent. Thus
the appropriate direction of movement is here determined in the sim-
plest way — by contraction of the part stimulated. Such effects are
produced by mechanical and chemical stimulations, by heat, by elec-
tricity, and apparently by light. In Hydra, as we have seen, identically

200 BEHAVIOR OF THE LOWER ORGANISMS

the same reaction has the opposite effect, subjecting the animal still
further to the action of the stimulating agent; other reactions must
supervene before the animal is removed from the stimulus. Intense
stimulation of the tentacles of the medusa or of the margin of the bell
induces, in Gonionemus, a direct contrac-
tion of the tentacles.

When the margin or under surface of
the medusa bell is locally stimulated, the
= manubrium behaves in a manner that is
of great interest. This has been described
by Romanes (1885) in the medusa Tzarop-
sis indicans. If the margin or under sur-
face of the bell is sharply stimulated with
a needle, the manubrium at once bends
over and applies its tip to the point stimu-
_ Fic. 125.—The medusa Tiaropsis lated (Fig. 125). The reaction is thus
indicans, applying its manubrium to a ° ° 3
point on the margin which has been V€TY precisely localized. How does it
stimulated. x, y, 2, cuts made for happen that the manubrium is able to
eect aay purposes. After Ro iocate exactly the point touched, and to

bend at once in that direction?

In answer to this question, Loeb presents a very simple explanation,
which deserves attention, as it is a type of many of the recent hypotheses
put forward to explain the behavior of organisms. According to Loeb,
this behavior is due simply to the spread-
ing out of the local contraction caused by
the stimulus. ‘‘Every localized stimulus
leads to an increase in the muscular tension
on all sides, which is most intense near the
stimulated spot. Now if we decompose
each of the lines of increase of tension eda bc
(aa’, ab’, ac’, ad’, ae’, Fig. 126) radiating Fic. 126. — Diagram to illustrate
from the stimulated spot, into a meridional Loeb’s explanation of the localization
component aa’, dd’, bb’, etc., and an equa- diortaa Gob. ee ae
torial component, it is evident that the
latter can have no influence on the manubrium. Only the meridional
components can have an influence, and of these the one passing through
the stimulated spot is the largest. This fact must necessarily cause a
bending of the manubrium toward the stimulated spot” (Loeb, 1900,
Pp. 32).

This explanation represents the behavior as of the simplest character
—a mere spreading of a local contraction from the point stimulated.
But is this view adequate to explain the facts? In the protozoa we

c

BEHAVIOR OF CGALENTERATA 201

have found that such local action is as a rule not adequate; that the
organism tests the environment; and the behavior at a given moment
depends on the success or failure of a previous trial. Is there anything
of this kind in the medusa, or does Loeb’s simple explanation exhaust
the matter?

This question is clearly answered by the experiments of Romanes.
He found that if a cut is made parallel to the margin, as at x, Fig. 125,
and a point lying below this cut is stimulated, the manubrium is no
longer able to locate precisely the stimulated point. It bends, but no
longer directly to the point stimulated. This, according to Loeb, is
exactly what we should expect. The cut interrupts certain of the lines
of tension, so that they no longer pull the manubrium to the precise spot.
His explanation, he holds, “also shows why an incision parallel to the
margin of the umbrella makes an exact localization impossible and only
allows uncertain movements toward the stimulated quadrant” (1900,
p- 32). It is easy to see that the manubrium, on Loeb’s theory of de-
composition of the lines of tension, would be pulled over in the general
direction of the stimulated spot, but might not strike it exactly.

Is this what happens? Let us examine the facts as set forth in
Romanes’ own words: “Although in the experiment just described
the manubrium is no longer able to localize the seat of stimulation in
the bell, it nevertheless continues able to perceive, so to speak, that
stimulation is being applied in the bell somewhere, for every time any
portion of tissue below the cut a is irritated, the manubrium actively
dodges about from one part of the bell to another, applying its extremity
now to this place and now to that one, as if seeking in vain for the of-
fending body. If the stimulation is persistent, the manubrium will
every now and then pause for a few seconds, as if trying to decide from
which direction the stimulus is proceeding, and will then suddenly
move over and apply its extremity, perhaps to the point that is opposite
the one which it is endeavoring to find. It will then suddenly leave
this point and try another, and so on, as long as the stimulation is con-
tinued” (Romanes, 1885, p. 112-113).

From Romanes’ description it is evident that the manubrium under
these circumstances may not even move in the general direction of the
point stimulated; he says expressly that it may move toward the oppo-
site point, or toward any other point. At times, he says, a manubrium
moves from point to point, “without being able in the least degree to
localize the seat of irritation.” The considerations adduced by Loeb
do not explain these facts; and his theory is quite inadequate to account
for the behavior. Contraction occurs, not merely as a direct spreading
from the point stimulated, but now in one place, now in another,

202 BEHAVIOR OF THE LOWER ORGANISMS

including even a region directly opposite that stimulated. The manu-
brium, having reacted once, does not cease, but in some way recognizes
its failure and tries again. In other words, failure changes its physio-
logical state, so that now it bends in a new direction. The whole
account given by Romanes is as vivid a description of the method of
reaction by the production of varied movements subjecting the organism
successively to different conditions, as it would be possible to imagine
under these circumstances.

It would be most interesting to determine whether the animal may
thus by trial finally discover the irritated spot, and later through repeti-
tion come to bend toward it directly, as it did before the cut was made.

5. THE Rejectinc REACTION OF SEA ANEMONES

In some sea anemones the presence of masses of waste matter on
the disk leads to the performance of activities which result in the re-
moval of the waste matter; this behavior we may call the rejecting reac-
tion. Such behavior is well seen in the large sea anemone Stoichactis
helianthus, found in the West Indies. This animal has a flat or concave
disk 10 to 15 cm. in diameter, covered closely with tentacles about
8 mm: in length. If a quantity of dead plankton, or a mass of sand,
or other waste matter, is placed on the disk, the animal sets in opera-
tion measures which remove it. Food placed on the disk of a speci-
men that is not hungry produces the same result. The behavior under
such circumstances is complex, and the removal of the waste matter
may be accomplished in more than one way.

The tentacles of that region of the disk bearing the waste body col-
lapse, becoming thin and slender and lying flat against the disk. The
disk surface in this region begins to stretch, separating the collapsed
tentacles widely. As a result the waste mass is left on a smooth, exposed
surface, the tentacles here having practically disappeared, while else-
where they form a close investment. Thus the waste is left fully ex-
posed to the action of the waves or currents, and the slightest disturbance
in the water washes it off. Under natural conditions this must result
in an immediate removal of the mass of débris. If this does not occur
at once, often the region on which the débris is resting begins to swell,
becoming a strongly convex, smooth elevation, thus rendering the wash-
ing away of the mass still easier.

But if the débris is not removed by the reaction just described, then
new activities set in. If the waste body is near one edge of the disk,
this edge usually begins to sink, while at the same time the tentacles be-
tween the edge and the waste mass collapse and practically efface them-

BEHAVIOR OF CELENTERATA 203

selves. Thus the mass slides downward off the disk. If this does not
occur at once, after a time the region lying behind the mass begins to
swell; it often forms in this way a high, rounded elevation. The waste
mass is now on a steep slope, and is bound soon to slide over the edge.
Sometimes by a continuation of these processes the entire disk comes
to take a strongly inclined position, with the side bearing the débris
below. Often one portion of the edge after another is lowered succes-
sively till all of the waste matter is removed and the disk is thoroughly
cleaned. The disk then resumes its horizontal position, with nearly
flat or slightly concave surface.

Sometimes the edge bearing the débris cannot be lowered, owing to
the fact that it is almost against an elevation in the irregular rock to
which the anemone is attached. In this case (after perhaps an attempt
to bend this edge downward) the part between this edge and the débris
swells and rises, rolling the mass toward the centre, while at the same
time the region beyond the débris sinks down. In this way the waste
matter is rolled across the disk to the opposite side, and dropped over
the edge. The process is slow, often requiring fifteen minutes to half
an hour.

This whole reaction -is characterized by great flexibility and vari-
ability. The débris sets in operation certain activities; if these do not
put an end to the stimulation, other activities are induced, till one is
successful. This is an excellent illustration of the general characteris-
tics of behavior in the lower organisms.

6. Locomotor REACTIONS IN HypRA AND SEA ANEMONES

After contracting in response to stimulation, if the stimulus still
continues, Hydra and the sea anemones usually set in operation other
activities, having a more radical effect in separating the animal from
the source of stimulation. We have examined certain cases of this
character in the foregoing section on the rejecting reaction. We shall
here consider such reactions as tend to remove the animal, or cause it
to take a new position.

Hydra. — After contracting in response to stimulation, Hydra usu-
ally bends over into a new position and soon extends again in a new
direction, just as happens in its spontaneous contractions (Fig. 114).
This may be repeated many times, the animal occupying successively
many different positions.

In bending thus into a new position in response to a one-sided stim-
ulus, does Hydra bend directly away from the source of stimulation?
Wagner (1905) and Mast (1903) have answered this question experi-

204 BEHAVIOR OF THE LOWER ORGANISMS

mentally. Wagner tried stimulating one side of the body mechanically,
while Mast raised or lowered the temperature of one side. Both authors
agree as to the following results: The direction of extension after con-
traction bears no definite relation to the side from which the stimulus
came; the animal is just as likely to extend toward the source of stimu-
lation as in any other direction. In other words, when stimulated,
Hydra merely changes its position, without special relation to the locali-
zation of the stimulating agent. The direction of bending and exten-
sion is determined by internal factors. If the stimulus is repeated, con-
traction occurs again, and the animal extends in still another direction.
The analogy of these relations with those shown by the infusoria is evi-
dent; the latter when stimulated usually merely change the direction
of movement, without regard to the direction from which the stimulus
came. In the infusoria the internal factors (structural in character)
which determine the direction have been determined; this has not yet
been done for Hydra.

But repeated or strong continued contraction, with extension in a
new direction, is not the final recourse of Hydra under strong stimula-
tion. If the stimulation continues, the animal finally bends over, places
its head against the surface to which it is attached, releases its foot, and
moves away from the spot where it has been subjected to such objec-
tionable experiences. The locomotion is usually of the sort illustrated
in Fig. 117. This reaction has been observed by Wagner (1905) under
mechanical stimulation, by Mast (1903) under stimulation by heat, and
by the present author under stimulation by chemicals. In all cases it
was found that the direction toward which the animal moves bears no
definite relation to the direction from which the stimulus comes. Wag-
ner stimulated one side repeatedly by striking it with a rod, and found
that the animal was as likely to move toward that side as in any other
direction. The experiments of Mast are particularly interesting in this
connection. Mast placed a considerable number of Hydras in a fat-
bottomed trough, and heated one end. At about 31 degrees C. the
animals began to release their foothold and move about from place
to place. But they were as likely to move toward the heated end as
away from it. The results of a series of such experiments are shown
in Fig. 127. In this figure are represented not only the movements of
locomotion, but also the different .directions in which the animal ex-
tended after contracting. The diagram shows clearly that both sets of
movements are quite without definite relation to the direction from which
the heat comes; their direction evidently depends on internal factors.
When it experiences the high temperature, the animal merely changes
its position, in a way determined by its structure or other internal fac-

BEHAVIOR OF C@LENTERATA 205

tors. If the high temperature still continues, it changes position again,
and thus continues till the high temperature ceases or the animal dies.
The behavior resembles essentially that of infusoria under similar con-
ditions. The reaction is very ineffective under the conditions shown in
Fig. 127, owing to the

slowness of the move- dg

ments of Hydra. Most

of the animals in the [ gg*e 4 33° 28° 23°
heated region finally die. F fe
But if the animals moved

would escape, and those
that moved ‘in the

wrong direction the first ¥
time would, after one 5

or two changes of di- . AR
rection, likewise get out ah
of the heated region.

The reaction would be ]|
of precisely the same
character as that of the [JS

infusoria. But the Fic. 127. — Diagram of the movements of a number of
action system of Hydra 17s yen cosnnng thm rsa th cd
1S evidently adapted ments of a single Hydra. The figures 1, 2, 3, etc., show the
only for meeting mmm dame deste ln wi ates ee
changed conditions over bers indicates that here the animal released its foothold and
a very limited area, such — inp repre shown to a new point of attachment.
as may be escaped by a
slight, slow movement. When the changed conditions cover too large
an area, the Hydra can only “try” its usual reaction; if this fails, it
must die.

A decrease of temperature does not cause Hydra to change.position.
As the temperature becomes lower, the animal merely becomes more
sluggish, contracting more slowly and at longer intervals, till finally,
near the freezing point, movement almost ceases (Mast).

As we have seen on page 194, an internal condition — hunger —
may induce the same locomotor reactions as are produced by continued
external stimulation. This is a matter which we shall take up again in

the account of food reactions.

rapidly and far at each | §

change of position, then \
those that moved. away m
from the heated side a } a. u

206 BEHAVIOR OF THE LOWER ORGANISMS

Sea Anemones. —In some sea anemones, as in Hydra, repeated
strong stimulation causes the animal first to contract, then to bend into
new positions, and finally to move away. Each of these reactions may
be repeated several times before the succeeding one occurs. There are
certain features of this behavior that are of much interest, since they lead
to results analogous to habit formation in higher animals. The facts
have been most carefully studied in Azptasia annulata.

Aiptasia is a rather slender, somewhat elongated actinian living in
crevices beneath and between stones. If stimulated by touching the
disk or tentacles with a rod, it contracts strongly. It then extends in
the same direction as before. When it is fully extended we repeat the
stimulus. The animal responds in the same way as at first. This con-
tinues usually for about ten or fifteen stimulations, the animal extending
each time in the same direction as at first. But at length, when stimu-
lated anew, the polyp contracts, bends over to one side, and extends in
a new direction. As the stimuli are continued, the animal repeats for a
number of times the contraction and extension in the new direction,
then finally turns and tries a still different position.

This change of position may be repeated many times. But in the
course of time the reaction becomes changed in a still different manner.
The anemone releases its foothold and moves to a new region. This
same reaction is produced in Cerianthus, as we have seen, by hunger.

Aiptasia frequently extends in most awkward turns, the body taking
and retaining an irregular and even crooked form. This is evidently
due to its life in irregular crevices and crannies. In order that its disk
may protrude into the open water, it is compelled to extend in the irreg-
ular ways mentioned, and to retain the crooked shapes thus produced.
When removed from its natural habitat, it still retains these irregulari-
ties of form and action, so that a collection of Aiptasias shows all sorts
of right-angled and zigzag shapes. It would appear that these irregu-
larities must have arisen as a result of the way in which the animal
extends in its natural surroundings. From this it would appear that a
method of extension frequently repeated must in the course of time
become stereotyped, forming what we are accustomed to call in higher
animals a habit.

If this is the case, then it should be possible to produce new stereo-
typed reaction forms, by so arranging the conditions that the animal
shall be compelled to extend always in a certain way (differing from
its former way), and to retain the form thus induced. In some speci-
mens this result is obtained with the greatest ease, and in a very simple
manner. Thus, in a certain case, an individual attached to a plane
horizontal glass surface was bent in extension far over to the left. Stimu-

BEHAVIOR OF CGELENTERATA 207

lating it repeatedly, it contracted at each stimulation, then bent, in
extending, again to the left. But after some fifteen stimulations it
turned away, and bent over to the right. Now when stimulated it con-
tracted as before, then bent regularly, in extending, over to the right.
It seemed to have acquired a new method of behaving, ane to
the right instead of to the left.

Close examination showed that the cause of this phenomenon is as
follows: When it contracts in response to stimulation, it does not re-
gain a completely symmetrical structure, but remains a little more con-
tracted on the side that is concave in extension. In extending anew,
this side still remains a little more contracted than the opposite one, so
the animal takes a curved form, concave toward the same side as in its
previous extension. In other words, the structure conditioning the
curved form is not completely lost even when the animal contracts, and
it becomes evident again on a new extension.

Thus in Aiptasia the formation of a stereotyped method of action .
depends upon very simple conditions. Yet there can hardly be a doubt
that the permanent individual peculiarities of form and action found
under natural conditions, as mentioned above, have risen in exactly
this way. It thus plays the part taken by what is called habit formation
in higher animals.

The facts set forth in the present section show clearly that the cce-
lenterates do not always react in the same way to the same external
stimulus. Internal conditions of the organism, as determined by past
stimuli received, past reactions given, and various other factors, are of
equal importance with external conditions in determining behavior. -
We shall see many further illustrations of this fact in the reactions
toward food.

7° ACCLIMATIZATION TO STIMULI

Besides the changes in behavior under constant stimuli that we have
described in the last section, there are certain others which may perhaps
be classed as acclimatization to stimulation. In sea anemones a light
stimulus that is not injurious may cause at first a marked reaction, then
on repetition produce no reaction at all, or a very slight one. Thus, a
drop of water is allowed to fall from a height of 30 cm. on the
surface of the water just above the outspread disk of Azptasia annulata.
The animal at once contracts completely. After the animal has
expanded, another drop is allowed to fall in the same way. As a rule,
there is no response to this or to succeeding drops. Sometimes there
is a reaction to the first two or even three drops, but usually. reaction
ceases after the first one.

208 BEHAVIOR OF THE LOWER ORGANISMS

Sometimes a slight reaction of a different character supervenes after
the stimulus has been repeated many times. The animal begins to
shrink slowly away from the region where the drops are falling, so that
in the course of time the disk has been withdrawn much farther be-
low the surface, though no decided reaction has occurred to any one
stimulus.

8. REACTIONS TO CERTAIN CLASSES OF STIMULI

In the foregoing sections we have taken up reactions to mechanical
stimuli, heat and cold, and chemicals; we shall have occasion to con-
sider some of these further in the account of food reactions. There are
certain other classes of external stimuli which may play a part in deter-
mining behavior in these animals; these we will take up separately.

A. Reactions to Electricity

Induction shocks have been much employed in experimental work
on contraction in coelenterates. The results of such stimulation do not

FPR ko.

1

Fic. 128. — Reaction of an attached Hydra to a constant electric current of moderate inten-
sity. 1-5, successive stages in the reaction. After Pearl (1901).

differ greatly from those produced by other forms of stimulation (me-
chanical, etc.), local or general contractions occurring in dependence
on the strength of the current. These may be followed by locomotor
movements.

The effects of the constant electric current are more peculiar and of
greater interest. They have been studied in Hydra by Pearl (1901);
in the medusa Polyorchis penicillata by Bancroft (1904).

Hydra. —In Hydra the constant current causes local bendings of
the body similar to those produced by sharply localized chemical and
thermal stimuli. If a weak current is passed through the water trans-
versely to the Hydra, the animal contracts on the anode side, at a point
a little above the foot, thus bending the body (Fig. 128). At the same
time or a little before, the tentacles which were in line with the current
contract (Fig. 128, a). Sometimes, further, there is a contraction on

BEHAVIOR OF CG@LENTERATA 209

the anode side just below the base of the tentacles. As a result of the
contraction on the anode side, the Hydra bends toward the anode. As
soon as it comes into a position with the anterior end directed toward
the anode, the entire body contracts, since a Hydra in this position is
stimulated more than in any other (Fig. 128, 5). In a stronger current
the complete contraction takes place first, then the animal slowly bends
over toward the anode. If, as sometimes happens, the foot is free while
the head is attached, the bending takes place as usual on the anode side.

I ae

Fic. 129. — Successive stages in the reaction of a Hydra to the electric current when the
foot is unattached. The foot becomes directed toward the anode. After Pearl (1901).

The result is necessarily that the foot becomes directed toward the anode,
so that in this case the orientation of the animal is the reverse of that
found in the specimens attached by the foot (Fig. 129). This result
shows clearly that the orientation to the electric current is due to the
direct local contractions caused by the current on the anode side, and
is not due to an attempt on the part of the animal by anything like a
process of trial to come into a certain definite position.

In a Hydra placed transversely to ‘the current, the tentacles con-
tract in a peculiar way. A weak current causes only the tentacles which
are in line with the current to contract, and of these, that extending
toward the cathode contracts more quickly and more completely than

+ -+@ x _= - =
A 2 | Magli:
: Cc €

Fic. 130. — Effects of the constant electric current on pieces of Polyorchis. After Bancroft
(1904). A, meridional strip passing through the manubrium. B, similar strip stretched out
in line with the current. C, isolated tentacles.

that directed toward the anode (Fig. 128, a). If the Hydra is lying

parallel with the current, the body contracts much more readily when

the anterior end is directed toward the anode than when it is directed

toward the cathode. In either of these positions the tentacles usually

remain extended, and somewhat inclined toward the cathode (Figs. 128

and 129). But if a very strong current is used, both body and ten-
4

210 BEHAVIOR OF THE LOWER ORGANISMS

tacles contract strongly. Pieces of the animal react in essentially the
same way as the entire organism, and young buds (with tentacles)
react in the same way as adults, but are more sensitive to the current
(Pearl, 1901).

Medusa. — If strips of various shapes are cut from the medusa.

Polyorchis, and subjected to the action of the constant current, the
tentacles and manubrium bend toward the cathode (Fig. 130, a, )).
This takes place even with isolated tentacles (Fig. 130, c). If the
current is long continued, such isolated tentacles partially relax, then
contract again. This is repeated, so that an irregular rhythmic con-
traction is produced by the constant current.

B.. Reactions to Gravity

The position of the body and the direction of locomotion are partly
determined in some of the Ccelenterata by gravity. There is great
diversity among different members of the group in this respect. In
some, gravity is an almost constant determining factor in the behavior.
In others it plays only an incidental part, affecting the behavior under
certain circumstances, while in still other cases it seems to have no effect

on the movements whatsoever. .

' We have already seen that the position taken by Cerianthus is partly
determined by gravity. The sea anemone Sagartia, according to Torrey
(1904), usually moves upward when this is possible, and at the same
time it tends to keep its body in line with gravity, with the disk above.
If while moving on the floor of the aquarium it reaches the perpendicu-
lar side, it at once begins to ascend. Since Sagartia creeps by move-
ments of its foot, remaining in the upright position, its ascent on a
vertical surface involves bringing the body into an oblique position,
in place of the usual perpendicular one. Thus its tendency to creep
upward interferes with its tendency to keep its body in line with gravity,
and the former prevails. Sagartia may also creep on the under side
of the surface film, with head down, so that it is by no means a rigid
requirement that the head shall be above. Doubtless many other sea
anemones will show a tendency to keep the body in a certain position
with reference to gravity.

In the hydroid Corymorpha, according to Torrey (1904 a), there is
a decided tendency to take a position with the head (or oral end) upward.
When placed in an inverted or oblique or horizontal position, Cory-
morpha rights itself by a bending of the body, which is due, according
to Torrey, not to muscular contraction, as in the sea anemones, but to
a change in the turgidity of the large axial entoderm cells. Those on

BEHAVIOR OF CQLENTERATA 2It

the lower side become more turgid, increasing in volume and thus bend-
ing the stem directly upward. Either the entire animal or a piece of
the stem, without head or foot, reacts in this manner. Thus the reaction
is in this animal comparable to the reaction to gravity in a plant.

But in many species of fixed ccelenterates gravity clearly has: little
or nothing to do with the usual position. Metridium, Aiptasia, Séot-
chactis helianthus, Condylactis passiflora, and many others are found
occupying all sorts of positions with reference to gravity, and the same
is true of Hydra and various hydroids.

In some meduse the movement is partly guided by gravity. Go-
nionemus, as we have seen, swims in its “fishing”? movements upward
to the surface. Yerkes (1903) found that this occurs in the same way
when the light comes from below, so that the guiding factor is apparently
gravity. This reaction to gravity is of course not constant; it occurs
only at intervals and under certain circumstances.

Careful examination will probably show that gravity plays a past in
certain episodes of the behavior of most of these animals, even though
it may not affect their usual position or direction of motion. Thus,
gravity plays a part in the “rejecting reaction” of the actinian Stoi-
chactis, described in Section 5 of the present chapter. The situa-
tion “ waste-matter-on-the-disk-not-removed-by-the-first-reaction ” is -
responded to by taking such a position with reference to gravity as re-
sults in removing the waste; then the reaction to gravity ceases. Simi-
lar transitory reactions to gravity, seeming to serve definite ends, are
found in many other animals. Thus, in the hermit crab, according to
Bohn (1903), we have such a case. While investigating a shell which
it may adopt as a home if fitting, this animal takes a certain position
with reference to gravity; namely, with body on the steepest slope of
the shell, and head downward. It then turns the shell over (the posi-
tion mentioned being the most favorable one for this action), and ceases —
to react with reference to gravity. Other cases of the same sort will be
described for the flatworm Convoluta (Chapter XII). Gravity has, of
course, many diverse effects on the substance of organisms, and in al-
most no case has its precise action in directing movements been deter-
‘mined. When an animal is inverted, this may cause a redistribution
- of the constituents of the body or of the separate cells. Such a redis-
tribution would probably interfere with the usual physiological pro-
cesses, and might therefore act as a stimulus to a change of position.
Again, in freely moving organisms, gravity causes differences in the
ease of movement in different directions, and such differences may
well determine the direction of motion. Again, a change in the usual
position with reference to gravity may induce unusual strains in various

“212 BEHAVIOR OF THE LOWER ORGANISMS

parts of the body, or may shift the weight of the body to.parts unaccus-
tomed to bearing it; and these effects might serve as stimuli to cause
the animal to take another position. This possibility will be vividly
realized by any one who undertakes to rest with a limb doubled in some
unusual position beneath him. Again, certain movements with refer-
ence to gravity may produce results involving a change of the conditions
affecting the organism, and since it is a well-established fact that the
results of behavior partly determine future behavior, this fact may
determine movements with reference to gravity. There seems to be
no @ priori reason why each of the relations above mentioned, as well
as various others, may not induce reaction in one organism or another,
and it seems not difficult to find probable examples of all. We have
been assured by various writers that the reaction to gravity must be
explained in the same way in all cases, but this is evidently said rather
in the capacity of a seer or prophet, than in the capacity of a man of
science whose conclusions are inductions from observation and experi-
ment.

C. Reactions to Light

Many of the sea anemones and medusz do not react to light, so far
as known. In other cases a reaction to light is very marked. The
relation of the behavior to light is in certain cases exceedingly complex,
and very instructive, as showing the numerous factors on which behavior
depends. We shall take up especially the reactions of Hydra, and of
the medusa Gonionemus.

(1) Reaction to Light in Hydra

The behavior of Hydra with relation to light has been studied es-
pecially by Wilson (1891). Both the green and the brown Hydra are
usually found at the lighted side of the vessel containing them. If they
are at first scattered, they will in a day or two be found to have moved
to the lighted side. If at the side of the dish next the window there are
attached light and dark strips of glass, the Hydras collect in the light
strips. If different colored lights are used, by placing strips of glass
of different colors on the lighted side of the vessel, the Hydras collect
in the blue light, while all other colors (except perhaps green, which
seems slightly effective) act like darkness. The animals gather in the
blue even in preference to the white light, which of course contains all
the blue rays. As to the way in which the reaction to light takes place,
the following facts were brought out by Wilson. A change from light
to dark, or from blue or white light to one of the colors which acts like

BEHAVIOR OF CE@LENTERATA 213

darkness, causes the animal to become restless and move about. The
motion seems undirected, but as soon as the animal comes into the blue
or white light, it becomes less restless, and remains. The behavior
is thus far, then, like the reaction to heat; the animal when not lighted
simply moves about in various directions, till one of its movements
brings it into light. Whether the animal when moving draws back or
stops on coming to the boundary of the light, where it would pass into
the darkness, as Euglena does, has not been determined. But when the
vessel is lighted from one side, the animal moves toward the source
of light, and the movement is no longer an irregular wandering, but
according to Wilson (1891, p. 432) is fairly direct. This is like the re-
action of Euglena, and it seems possible that in Hydra the reaction is
produced in the same manner as in that organism. If this is true,
there is a tendency for the moving animal to keep its anterior end directed
toward the light, due to the fact that when it turns this end away, the
change to relative obscurity at the anterior end causes further move-
ment, till the light again falls on the anterior end. The movements
should be studied further to determine this point. Fixed Hydras do
not maintain any particular orientation with reference to the light rays,
but change their position frequently, in the way illustrated in Fig. 114.
The green Hydra moves to the lighted side of the vessel more rapidly
than the yellow Hydra. This is probably due to the generally more
rapid movements of the green species.

In a powerful light the reaction of Hydra, like that of most other
positive organisms, becomes reversed. The animals collect in the
shadow of leaves or on the bottom. They have not been observed to
move directly away from the source of light (Wilson, 1891), so that the
reaction is probably an irregular wandering based on the method of
trial.

Hertel (1904) found that both the green and the colorless Hydra
react by contraction when subjected to powerful ultra-violet light. These
rays killed the colorless Hydra in about one minute, while Hydra viridis
resisted their action for six to eight minutes.

The gathering of Hydras in lighted areas and the movement toward
a source of moderate light are of much benefit to the animals in obtain-
ing food. Hydra preys upon small crustacea and other minute animals,
and these gather as a rule at the lighted side of the vessel. By taking
a position on this side, the Hydras find themselves in the midst of a dense
swarm of organisms and are able to capture much food. When in such
situations one frequently finds them gorged with prey. In other parts
of the vessel they would have almost no opportunity of obtaining food

(Wilson, 1891).

214 BEHAVIOR OF THE LOWER ORGANISMS

(2) Reactions to Light in Gonionemus

The relation of the behavior of the medusa Gonionemus to light, as
studied by Yerkes (1902 a, 1903), is exceedingly complex; it can by no
means be expressed by any simple formula. In examining the matter
it will be well to consider first the relation of the light to the amount
of activity shown by the animal; then the nature of the activities in
constant lights of various intensities; then the effects of changes of
illumination.

In ordinary daylight, Gonionemus continues its usual activities,
swimming about by rhythmical contractions, and pursuing its usual
occupation of “fishing” (p. 192). It is not clear that the direction of
its movements has any relation to the direction of the rays of light, so
long as all conditions remain uniform. If the light comes from below
instead of above, Yerkes (1903) found that Gonionemus continues to
swim to the top and float to the bottom, as before.

If the light is cut off, the medusa usually comes to rest after one to
five minutes. By covering the vessel containing them, it is thus possible
to bring the animals to rest for experimental purposes. In continued
darkness the animal is much less active than in the light.

In strong sunlight the animal becomes very active. At first it swims
toward the source of light, thus rising under natural conditions to the
surface of the water. Later its reaction changes; it stops coming to the
surface, begins to avoid the light, and swims toward the bottom. It
may now persistently strike against the bottom in its efforts to swim
away from the source of light. Sometimes in a strong light it places
the more sensitive subumbrellar surface against the bottom and comes
to rest. At times its activities become, under the action of direct sun-
light, uncodrdinated; it moves upward in its contraction, downward
in its expansion.

In a moderate light coming from one side the behavior of Gonio-
nemus is at times very peculiar. When the conditions are quite uni-
form, as we have seen, its movements often show no relation to the direc-
tion of such a light. But when the light first begins to act, as when a
jar containing medusz is placed near a window, they at first swim
toward the source of light. The medusz thus gather at the lighted side
of the vessel. But after a time, if undisturbed, they cease to react to
light, and may scatter throughout the vessel. If there are regions of
light and shade, the animals now usually gather in the shaded region.
But if they are again disturbed in some way, as by stirring up the water,
they swim toward the light again, — later scattering as before, when
the conditions become uniform.

BEHAVIOR OF CGLENTERATA 215

Thus the reaction of the animal depends on its physiological state;
when excited it moves toward the light, otherwise it is indifferent or
gathers in the shade. In the flatworms we find a parallel condition of
affairs, but with the relations reversed. It is not unlikely that the
tendency of: the medusa to go toward the light when disturbed is related
to its usual method of life, and has a functional value. The animal
when at rest is commonly attached to the vegetation of the bottom.
When disturbed by a large animal foraging among the plants, it would
move toward the light, hence out into the free water and upward, thus
escaping the enemy.

Thus far we have considered the behavior under light of constant
intensity. Let us now see the effects of sudden changes in intensity
of illumination. Here we find again that the effect of a given change
depends on the state of the animal. If the medusa is at rest on the
bottom, a sudden marked increase in the intensity of the light usually
causes a sudden contraction of the bell. As a result the animal, of
course, swims away from its first position. Sometimes, however, an
increase of light merely causes an animal that is at rest with the sensitive
concave surface up to turn over, so as to bring the sensitive surface
against the bottom, where it is little affected by the light. In a case
described by Yerkes, increase of light caused regularly this turn with
bell up, while decrease caused a return to the “bell down’’ position.

A decrease of light usually has no effect on a resting Gonionemus.
But sometimes it causes contraction, so that the medusa swims away.
In such specimens an increase of light usually causes no reaction. Some-
times, however, a given specimen reacts both to increase and decrease
of illumination.

Thus the reaction of a resting medusa to a change of illumination is
variable, depending on the individual. Doubtless in a given individ-
ual it varies with the physiological state and past history of the animal.

In the swimming Gonionemus, usually both an increase and a de-
crease of light cause the animal to expand, cease swimming, and sink to
the bottom. Here it usually remains for a time, then resumes activity.

If a vessel containing a number of the medusz is divided by a line
x-x into two regions, one brightly illuminated, the other shaded, the
animals usually behave as follows: A specimen swimming about in
the light region crosses in its course the line x—«, passing into the shade.
It at once ceases swimming and sinks to the bottom. Here it remains
for a short time, then continues to swim about in the shaded region.

If a specimen swimming in the shaded region crosses the line «—«
into the light, it likewise sinks to the bottom and remains quiet for a
time. Now, .upon resuming activity, it swims in such a way as to pass

216 BEHAVIOR OF THE LOWER ORGANISMS

back into the shade. Yerkes is convinced, from analogy with the effects
of other stimuli, that this is due to a stronger contraction on the side
most intensely lighted — that farthest from the shadow. This would,
of course, turn the medusa back into the shade.

Thus in the course of time practically all the medusz in the vessel
will be found in the shaded region.

In the behavior of Gonionemus with relation to light there are evi-
dently a number of paradoxical facts. The medusa swims toward the
source of light, yet tends to gather in shaded regions. It goes at first
toward a source of strong light, later reverses this reaction. It moves
toward the source of light when excited, but becomes indifferent when
undisturbed. Different individuals react differently to the same con-
ditions, and the same individual reacts differently at different times.
We have here an excellent illustration of the fact that the reactions of
organisms, even to simple agents, depend on a multiplicity of factors.
If we could study the medusa in the natural conditions under which it
lives, and if we knew thoroughly the physiological processes taking place
within it, we should doubtless find all these peculiarities explained,
and should probably discover that its reactions are regulatory. When
we carry such an animal to the laboratory and experiment upon it there,
it is like removing an organ from the body and studying it in a dissect-
ing dish. We cannot understand its activities without knowing their
relations to the rest of the body — to the environmental conditions.

9g. BEHAVIOR OF CG@ELENTERATES WITH RELATION TO Foop

The behavior of organisms is largely determined by the relation of
the environment to their internal physiological processes. In no field
is this so striking as in the relation of behavior to the obtaining of ma-
terial for carrying on the processes of metabolism. Under this point of
view come the reactions of organisms with reference to food, and to the
gases necessary for respiration. These reactions in the Coelenterata we
shall take up now.

A. Food and Respiratory Reactions in Hydra

Hydras are usually found in the upper parts of a vessel of water,
near the surface. This is not due to a reaction to gravity, but rather
to the relative quantity of oxygen in different parts of the water. If
‘an experiment is arranged in such a way that the lower surface of the
vessel is free and in contact with air, while the upper is not, the Hydras
tend to gather near the lower surface (Wilson, 1891). Collecting in

BEHAVIOR OF C@LENTERATA 217

oxygenated regions is probably brought about through a process of
trial, the organisms wandering irregularly till they come into oxygen-
ated regions and there remaining. If the water is allowed to become
very foul, all the Hydras soon collect at the very upper surface, often
in contact with the surface film itself.

Let us now examine the usual behavior of Hydra in obtaining food,
as described by Wagner (1905). As we have seen, the undisturbed
green Hydra changes its position at intervals, thus in the course of time
exploring thoroughly all the region about it. The tentacles of the green
Hydra are comparatively short, so that such exploring movements are
needed. In the colorless Hydras the tentacles are often excessively long
and slender, lying in coils on the bottom, and almost filling the sur-
rounding waters with a network of fine
threads. They may reach three or
four inches in length. In these spe-
cies changes of position are less
frequent, the great length of the
tentacles rendering this unnecessary.
When a small animal comes in con-
tact with one of the tentacles, in a
typical case a somewhat complicated
reaction occurs. The nematocysts of , Fi. 13t-—Hydra endeavoring to swal-

_ ‘ Be low a large annelid. Camera drawing.

the region with which the animal

comes in contact are shot out, causing the organism to cease its move-
ments. The tentacle is viscid and clings to the animal. Now the
tentacle is bent toward the mouth. At the same time the other ten-
tacles bend in the same direction. If the animal is a large one and is
inclined to struggle, the other tentacles seize it, and many nematocysts
are shot out and pierce it, so that the organism may become quite
covered with these structures. An insect larva which was rescued from
a Hydra at this stage is shown in Fig. 132, B. Meanwhile, the mouth
becomes widely opened, sometimes before the prey comes in contact
with it. When the food reaches the mouth, the tentacles usually release
it and are folded slightly back, while the edges of the mouth, or “‘lips,”
actively work up over the food, till it is enveloped and passes into the
cavity of the body. In this way a Hydra often takes organisms much
larger than itself. Figure 131 shows such a case, where a Hydra en-
deavored to swallow an annelid that was, at a moderate estimate, fifty
times its own bulk. The mouth and body were immensely distended,
and the worm was about half enveloped. The Hydra seemed then to
have reached its utmost limit, and the process stopped.

We now wish to analyze this complicated behavior, determining as

218 BEHAVIOR OF THE LOWER ORGANISMS

far as possible the nature and causes of the different factors which make
it up. We may ask first, What is the cause of the discharge of the
nematocysts ?

Near each nematocyst there is a projecting point, the cnidocil (Fig.
132, cl). This has often been compared to a trigger; touching the
cnidocil is said to cause discharge of the nematocyst. ‘That is, it is sup-
posed that a mechanical stimulus is the cause of the discharge. But
experiment does not bear out this supposition. Hydra may be rubbed
roughly with a needle, without causing discharge of the nematocysts.

Hard organisms, such as Os-
tracods, may strike against
it or run over its surface,
brushing against many cnido-
cils, yet no nematocysts are
discharged. On the other
hand, various chemicals
readily cause discharge of
the nematocysts; a solution
of methylene blue or methyl
green, for example, produces
this effect in a marked de- |
gree. Apparently, then,
some chemical stimulus must
be associated with the me-

Laer chanical stimulus in order to
4. ed Memon et sconin Hire. cause discharge of the nema-
tocysts; cl., cnidocils. B, insect larva covered with tocysts. Chemical stimuli
nematocysts as a result of capture by Hydra. of one sort or another will
doubtless usually be received from the organisms which serve as prey.
~ To what is the remainder of the behavior due? One thing which
must be noticed first is that the food reaction depends upon the physio-
logical condition of the animal. Not all Hydras react to suitable
food, but only those which have not been recently fed. It is, of course,
not surprising that only hungry Hydras should eat. Yet this brings out
the important point that the behavior is not an invariable reflex, but
depends on the physiological state of the organism.

When the animal eats, are the determining factors of the reaction
mechanical stimuli or chemical stimuli? Experiment shows that me-
chanical stimuli alone do not induce the food reaction. If bits of filter
paper, or ostracods with a hard shell, are brought in contact with the
tentacles or the mouth of a hungry Hydra, they are not swallowed. But
if the filter paper is soaked in meat juice, or if the ostracod is crushed,

-BEHAVIOR OF C@LENTERATA 219

then they are readily swallowed. A chemical stimulation is a necessary
factor in producing the reaction. But under usual conditions the chemi-
cal alone — the meat juice — will not produce the food reaction. There
must be a combination of chemical stimuli (of the proper character) and
of mechanical stimuli before the reaction is induced.

But when the Hydra is very hungry — when it has starved for a long
time — then a suitable chemical stimulus acting alone will produce the
food reaction. Placed in a solution of extract of beef the very hungry
Hydra opens its mouth widely and takes in the fluid. What seems
very remarkable is that a solution of quinine produces this effect as well
as does extract of beef (Wagner, 1905).

Thus the food reaction is throughout dependent upon the physio-
logical condition of the Hydra. Hydras that are not hungry will not eat
at all; moderately hungry specimens will take the solid food (chemical
and mechanical stimuli); very hungry ones take liquid food (chemical
stimulus alone). Hungry Hydras show still further modifications in
their behavior, compared with those that are not hungry. As we have
previously seen, they frequently contract and change to a new position
and even move about from place to place. Wilson (1891) records a
remarkable cycle of behavior in hungry yellow Hydras. Hydras usually
remain, as we have seen, in the upper layers of the water, on account
of the oxygen there found. But when the crustacea on which the ani-
mals feed have become very scarce, so that little food is obtained, Hydra
- detaches itself, and with tentacles outspread sinks slowly to the bottom.
Here it feeds upon the débris composed of dead organic matter which
collects at the bottom, often gorging itself with this material. It then
moves toward the light, and at the lighted side again upward to the
surface. Here it remains for a time, then sinks again and feeds upon
the material at the bottom. This cycle may be repeated indefinitely,
requiring usually some days for its completion.

B. Food Reactions in Meduse

The food reactions have been studied most carefully in Gonione-
mus. In this animal, as we have seen, there is a definite set of “fish-
ing’? movements, having the function of obtaining food. These move-
ments are of course not direct reactions to food, but are, so far as food
is concerned, spontaneous movements of the animal. If food is brought
near a resting medusa, this sets the animal to moving. If a piece of
fish is placed at one side of the medusa, it does not move directly toward
the food, according to Yerkes (1902 a). After a few seconds the ten-
tacles nearest the food begin to move about irregularly, and this gives

220 BEHAVIOR OF THE LOWER ORGANISMS

them a chance to find the food if it is very near. If they do not find it,
“there soon follows a general contraction or series of contractions of
the bell, which may take the animal either toward or away from the
source of the stimulus.”” Thus the medusa is induced by the presence
of food to swim about, and it usually in this way sooner or later comes
in contact with the food (Yerkes, 1902 a, p. 438). The behavior is
throughout not a definitely directed action, but an excellent example
of the method of trial — of what we call searching, in higher animals.

When the tentacles actually come in contact with food, they con-
tract and twist about each other in such a way as to hold it. The group
of contracting tentacles then bends toward the mouth, and that portion
of the margin of the bell bearing them contracts, drawing them nearer
the mouth. The manubrium bends toward the food, placing the mouth
against it, and the food is enveloped by the lips and swallowed.

What are the determining factors in this behavior? Doubtless, as
in Hydra, internal conditions play a part in determining the reaction to
food bodies, but this matter has not been studied in the medusa. As
to external factors, Yerkes (1902 a) has brought out the following: In
Gonionemus the entire food reaction may be produced by chemicals
alone. If with a pipette a strong infusion of fish meat is applied to the
tentacles, they twist and contract, bending toward the mouth, while the
manubrium as usual bends toward the tentacles stimulated. Solutions
of common inorganic chemicals do not produce this result; the tentacles
merely contract from them, remaining straight. If the infusion of fish
meat is made very weak, the animal begins the food reaction, contract-
ing and twisting the tentacles; but the reaction goes no farther. In rare
cases Yerkes (1902 a, p. 439) found that the animal begins the food re-
action when a very weak inorganic chemical, such as an acid, is applied
to it. But this quickly ceases, before it has gone far. The medusa in
such cases makes what we call in higher animals a mistake, but changes
its behavior as soon as it discovers the mistake.

Mechanical stimuli of a certain sort may likewise produce the food
reaction. With regard to this we find in Gonionemus certain peculiar
and most suggestive relations.

If the tentacles come in contact with some quiet object, or are touched
with a rod or a needle, they merely contract, remaining straight, as
when they are affected by inorganic chemicals. The response is clearly
a negative reaction, not a food reaction. But if the tentacles are touched
in a peculiar way, by drawing the rod quickly across them, they behave
differently. They quickly react and twist, just as when they touch a
piece of meat. Then they bend toward the mouth, the margin bearing
them contracting inward as usual, while the manubrium bends toward

BEHAVIOR OF C@LENTERATA 221

them. Finding no food, the swallowing movements of the manu-
brium do not occur. Thus “motile touch,” as Yerkes (1902 a) calls it,
causes the food reaction, while the touch of an object that is at rest
causes only a negative reaction. This reaction to a moving object
shows clearly the adaptation of the behavior to the natural conditions
of life. Usually, when something moves quickly along the tentacles of
a medusa, this will be a fish or other small animal, well fitted to serve
as food. So the medusa reacts to such a moving thing in such a way
as to seize it and bear it to its mouth. If the object turns out not to be
good for food, as is rarely the case, there is of course no harm done,
and it may be rejected. If the medusa comes in contact with an ob-
ject that is not moving, this will probably be a stone or plant or other
object not fit for food, hence the animal makes no attempt to take it.
The behavior is based, at it were, on the probability that any given
case will correspond to the usual condition. Movement serves to the
medusa as a sign of something living and fit for food, just as it does to
hunters among higher animals and even among men.’ It is a most in-
teresting fact that the positive reaction to a moving object is more rapid
than to a quiet one, even though the latter is actually food, while the
former is not. The reaction time for a moving object was found by
Yerkes (1902 a, p. 440) to be about 0.30 to 0.35 seconds, while the
reaction time for quiet objects or food is 0.40 to 0.50. This is again
directly adapted to usual conditions; to a moving animal reaction must
be rapid, or it is useless. One can hardly do otherwise than hold that
this specialized reaction to moving objects, so appropriate to the natural
conditions of the animal, is not a primitive reflex, but must have been
historically developed in some way, and that it would not occur if it
were not in the long run beneficial.

C. Food Reactions in Sea Anemones

In sea anemones the dependence of the reactions toward food and
other agents on the physiological state of the animal, particularly as
determined by the progress of metabolism, is very striking.

Finding Food. — Sea anemones remain for the most part quiet, with
disk and tentacles outspread, depending for food largely on the acci-
dental contact of moving organisms with these organs. But there are

1In this, as in other cases, such expressions as “serves as a sign” of course does not
affirm a mental sign, concerning which we have no knowledge in animals outside of the
self. It signifies merely that movement does, as a matter of fact, cause a reaction which
is appropriate to something usually accompanying the motion, so that the behavior is
objectively identical with that due in higher animals and man toa stimulus that serves as
a sign.

222 _ BEHAVIOR OF THE LOWER ORGANISMS

certain active movements which assist in procuring food. In most sea
anemones light stimulation of the tentacles, however produced, causes
these organs to wave back and forth, just as happens in meduse; this
increases the chances of coming in contact with food. In Sagartia, ac-
cording to Torrey, the presence of food near one side of the animal,
resulting in weak chemical stimulation, gives rise to more definite move-
ments. Part of the tentacles bend toward the food, contracting on the
side most strongly stimulated, while others bend toward the mouth. The
animal may at times bend its body toward the food, thus securing it.
The tendency of the tentacles to bend toward the mouth, as if carrying
food, when stimulated in almost any way, is very striking in many
coelenterates. In Sagartia the tentacles when touched bend first toward
the side stimulated, then toward the mouth. In the hydroid Cory-
morpha, according to Torrey (1904 a), the tentacles when thus stimulated
bend only toward the mouth. This bending toward the mouth of course
serves the function of carrying food, and it seems to have become the
reaction to all sorts of stimuli, on the chance, as it were, that it will serve
this function, in the given case. The plan of the behavior is that of
trial of a reaction that is beneficial under most circumstances.

The Taking of Food. —In the actual taking of food the behavior
varies greatly in different sea anemones. In some species ciliary move-
ment plays the chief part in the process,’ though assisted by muscular
contractions. In others, bodily movements brought about by muscles
are the main factors. Two or three examples will illustrate the principal
variations in this matter. ;

‘The common Metridium marginatum of the east coast of the United
States is an example of the species in which ciliary movement is perhaps
the chief agent in food-taking. Under usual conditions the tentacles are
pointed away from the mouth, and are covered with cilia, which beat
toward the tip of the tentacle. Thus small particles falling on the ten-
tacles are carried outward by the cilia and removed from the animal.
But if the particle is something fit for food, the behavior is changed.
When a bit of crab’s flesh is dropped among the tentacles, they contract
on the side touched, thus grasping the flesh. They then bend inward,
arching over with tips toward the mouth. The cilia, continuing to strike
toward the tip, now of course carry the food toward the mouth instead
of away from it. In time the meat drops from the tip of the tentacles
into or near the mouth.

The inner surface of the cesophagus, or tube into which the mouth
leads, is covered with cilia, which beat outward (save in the two grooves
at the angles, known as the siphonoglyphes). They thus bear outward

* For details’ regarding this for many different species, see Carlgren, 1905.

BEHAVIOR OF CGELENTERATA 223

any indifferent particles which may fall in the cesophagus. But when a
piece of meat is dropped into the mouth, the cilia at once reverse, now
beating inward. They thus carry the food into the digestive cavity of
the animal.

Meanwhile, the muscles surrounding the mouth, and those of the
cesophageal tube, contract in such a way as to produce swallowing move-
ments, which aid in ingesting the food. These swallowing movements
may begin while the food is still held by the tentacles, showing that the
stimulation from the food has been transmitted.

In Aiptasia annulata there are cilia which act in the same manner
as in Metridium, but the chief réle in food-taking is played by move-
ments of the tentacles and cesophagus. Ifa small object comes in con-
tact with a tentacle, it adheres to the surface, and the tentacle contracts
strongly, the entire animal usually contracting at the same time. Then
_ the tentacle bends over and places the food with considerable precision
on the mouth. The adjacent tentacles likewise bend over and are ap-
plied to the food body, holding it down against the mouth, The latter
then opens, the lips seizing the food, while the tentacles may release it
and bend away. The swallowing of the food is mainly due to the activi-
ties of the lips and cesophagus. In’this animal a bit of food may be
completely enclosed within ten seconds of the time it touches a tentacle.

In the large sea anemone Séoichactis helianthus, cilia seem to play
no part in the taking of food. In this animal the disk may be 10 to
15 cm. in diameter. If a piece of crab meat is placed on the disk
of a hungry specimen, the tentacles immediately surrounding it be-
‘gin suddenly to wave back and forth. This movement stops for a
few seconds, then begins again. All the tentacles that come in contact
with the food bend over against it and shrink, so as to hold it down
against the disk. Now that portion of the disk bearing the food begins
to sink inward, the mouth begins to open, and the walls of the cesopha-
gus protrude from the mouth as large bladderlike lobes. The region
between the mouth and the food contracts, the tentacles which it bears
collapsing and almost completely effacing themselves. By this con-
traction the mouth and food are caused to approach each other, the
intervening region almost disappearing. The cesophageal lobes in-
crease in size, becoming 3 or 4 cm. long and half as thick; they
extend toward the food, finally reaching it. The mouth may, in the
way described, be transferred from the centre of a disk 10 cm. in
diameter to within 1 cm. of the edge. Now the cesophageal lobes
extend over the food, while the tentacles progressively withdraw from
it, till the food is lying on the contracted part of the disk, completely
covered by the cesophageal lobes. Now that part of the disk below the

224 BEHAVIOR OF THE LOWER ORGANISMS

food withdraws, by an extension and displacement of the mouth, till
there is nothing beneath the food body, and it is pressed by the ceso-
phageal lobes into the internal cavity. The lobes then withdraw and
the mouth closes.

The determining factors in the food reaction are partly internal,
partly external, the variations of the former playing perhaps the most
important part. Many of the sea anemones are voracious, taking food
until the body forms a distended sac. But in most species, if not all,
the behavior changes decidedly as the animal becomes less hungry, and
after a time it refuses to take food, even removing it if the food is ap-
plied to the disk. The changes in reaction as hunger decreases seem
less marked in those species in which the food is taken mainly by ciliary
action.

Specimens that have not been fed for a long period frequently swallow
indifferent bodies, such as pellets of paper, grains of sand, and the like.
This has been observed in Aiptasia (Jennings, 1905 a), Sagartia (Torrey,
1904), Metridium (Allabach, 1905), and in a number of Mediterranean
anemones (Nagel, 1892). In Stoichactis the taking of such indifferent
bodies is rare, but sometimes occurs. In Sagartia and Metridium such
indifferent bodies cause a reversal of the beat of the cesophageal cilia,
just as is occasioned by actual food. All together, it is clear that in
hungry specimens of various sea anemones mechanical stimuli acting
alone may cause the food reaction.

In some cases chemical stimuli acting alone produce the food re-
action. If filtered crab juice is applied to the tentacles of Metridium,
they arch over toward the mouth. If the juice reaches the mouth, the
cilia of the cesophagus are reversed, striking inward, just as when a
piece of meat is present. The swallowing movements of the cesopha-
gus may likewise take place under chemical stimulation. Parker (1905)
has lately found that certain inorganic chemicals, containing potassium,
will cause the cilia to reverse and beat inward; this is the case for ex-
ample, with KCl and KNO,. But the reversal which takes place under
the action of meat juice is not due to the potassium salts which it con-
tains, for it requires a concentration of the potassium salt to produce
this result that is much greater than that existing in meat juice. In
Adamsia, according to Nagel (1892), the tentacles react to.sugar in the
same way as to meat juice; this is not true for Metridium and Sagartia.

As sea anemones become less hungry they usually cease to react to
such indifferent bodies as grains of sand, pellets of paper, etc., though
they still take crab meat readily. In Metridium and Sagartia bits of
paper no longer cause the reversal of the oesophageal cilia, by which
particles are carried to the mouth, while crab meat still produces this

BEH AVIOR OF C&LENTERATA 225

effect. In Azptasia annulata the tentacles no longer carry pellets of
paper to the mouth, but bend backward along the column and drop
them. In the Stoichactis that is not very hungry such indifferent bodies
are removed by the rejecting reaction described on page 202.

As the sea anemones become still less hungry the reaction to even
such food bodies as pieces of crab meat becomes changed. The reaction
gradually becomes slower and less precise. In a hungry specimen of
Aiptasia the food reaction is rapid, often requiring but ten or fifteen
seconds. But after several pieces of meat have been taken, the reaction
occupies a much longer period. The tentacles touched by the food may
not react for several seconds, then they bend in a languid way toward
the centre of the disk, while the adjacent tentacles may not react at all.
The food body is not placed so accurately on the mouth as before. At
a later stage food applied to the tentacles induces no reaction at all, or
a withdrawal of the tentacles, while if it is applied directly to the mouth
it is very slowly swallowed. In Stoichactis at this stage food is often
carried toward the mouth, then after or even before it reaches the mouth
the reaction is reversed and the food is rejected. If two pieces of meat
are applied at once to the disk of Stoichactis when in this condition, one
may be swallowed while the other is rejected. Often in Aiptasia one
piece may be rejected, while the immediately following piece is swal-
lowed. The animal seems in a condition of most unstable equilibrium,
so that the reactions are most inconstant and variable. No one could
suppose, in studying the behavior of a sea anemone in this condition,
that the behavior of such organisms is made up of invariable reflexes,
always occurring in the same way under the same external conditions.

As the animal becomes satiated, the food reaction ceases completely.
Pieces of crab meat placed on the disk of a Stoichactis in this state are
removed by the rejecting reaction already described. Aiptasia either
does not react at all when food is applied to the tentacles, or the ten-
tacles contract and bend backward —a negative reaction.

Some anemones are exceedingly voracious, seeming to take food as
long as it is mechanically possible for them to do so. This seems to
be the case, for example, with Metridium, where the changes in reaction
as the animal becomes filled with food are almost lacking. It may feed
till the body cavity becomes so completely filled as to cause disturbance
of function. As a result the entire mass of food is sometimes disgorged
undigested. After this has occurred, Metridium will often take food as
before. But in most sea anemones the taking of food ceases before any
such disturbance has been produced.

The rejection of food is not determined merely by the mechanical
fulness of the digestive cavity, but is evidently due to the effects of food

Q

226 BEHAVIOR OF THE LOWER ORGANISMS

on the internal processes. An Aiptasia (species undetermined), studied
by the present author, continued to take filter paper till the body was a
swollen sack, and pieces of the paper were repeatedly disgorged. But
new pieces, and even those that had just been disgorged, were readily
swallowed when applied to the disk. But when specimens of this
Aiptasia were fed considerable quantities of meat, they refused to take
either more meat or paper.

The reactions of well-fed sea anemones differ in many other ways
from those of hungry specimens. -They are much less inclined to react
to stimuli of all sorts. A disturbance in the water, or a touch with a
needle, that would produce a strong contraction in the hungry animal,
often causes no reaction whatever in the satiated specimen. A much
stronger solution of any given chemical is required to produce contrac-
tion than in the well-fed individual. If we should attempt to determine
the strength of a given chemical that caused contraction in Aiptasia, we
should get totally different results, according as we employed specimens
that were very hungry, or only moderately hungry, or thoroughly satiated.

Another factor influencing the food reactions of the sea anemone is
fatigue, and the effects due to this are easily mistaken for phenomena
of a different character. If the tentacles of a certain region of the disk
of Metridium are given many pieces of food, one after the other, they
refuse after a time to take the food, though the other tentacles will still
take food readily. In taking food very large quantities of mucus are
produced, and it is not surprising that many rapid repetitions of this
process exhaust the tentacles. If they are allowed to rest five to ten
minutes, they usually take food as at first.

As the fatigue comes on, the tentacles first cease to react to weak
stimuli, such as are produced by plain paper, or paper soaked in meat
juice; later to strong stimuli, such as that produced by meat. If meat
and paper are given in alternation, the tentacles will thus at first take
both; then they come to refuse the paper, while the meat is still taken.
Later they come to refuse the meat also.

The reaction to food varies also with certain other conditions. In
Metridium and Aiptasia the following is often observed: A specimen
refuses to take bits of filter paper, though it still takes meat. After it
has thus refused paper, two or three pieces of meat are given in succes-
sion, and taken readily. Now the bit of paper is placed again on the
disk, and it too is swallowed. Clearly, the uninterrupted taking of a
number of pieces of meat changes the physiological condition in some
way, preparing the animal for the taking of any object with which it
comes in contact. One cannot fail to note the parallelism with what
occurs in higher animals under similar conditions.

BEHAVIOR OF CG&:LENTERATA ; 227

Io. INDEPENDENCE AND CORRELATION OF BEHAVIOR OF DIFFERENT
PARTS OF THE Bopy

There is a general agreement among those who have studied the
behavior of coelenterates that the different parts of the body show re-
markable independence in their reactions. The tentacles of the sea
anemones and medusz react to most stimuli in essentially the same
manner when cut off from the body as when attached. The isolated
tentacles of Gonionemus react to meat juice by contracting and twist-
ing, as in the usual food reaction, while to inorganic chemicals they react
by a straight contraction, as in the negative reaction of the medusa
(Yerkes, 1902 6, p. 183). In Sagartia (Torrey, 1904) and Metridium
(Parker, 1896) the separate tentacles react to meat juice by bending
toward the side which formerly looked toward the mouth. Thus
each tentacle must contain within itself the apparatus necessary for its
usual reactions.

The fact that the tentacles have their own reactions independently of
the rest of the body is illustrated in a curious way in Loeb’s experiment
on heteromorphosis in Cerianthus (Loeb, 1891). He succeeded in
causing tentacles to develop at one side of the animal, forming a group
not associated with a mouth. These tentacles reacted to food as usual,
seizing upon it, and bending over with it in the direction in which,
under normal conditions, a mouth would be found. Here it was pressed:
down for a time, then released.

Like the tentacles, other parts of the body may react independently.”
Yerkes (1902 5) cut off the manubrium of Gonionemus and pinned it
by its base to the bottom of a dissecting dish. It now bent toward food,
seized upon and swallowed it, just as in the uninjured medusa. Many
experiments with similar results are described in the work of Romanes
(1885). Parker (1896) isolated a small bit of the ciliated epithelium
of the cesophagus of Metridium. He found that this reacted to meat
juice by a reversal of the ciliary stroke, just as happens in the uninjured
animal. In Actinia, Loeb (1891) found that if the head is cut off, the
lower part of the animal will take food through the cesophageal opening.
If the animal is cut in two, even the open lower end of the upper half
will take food, just as will the mouth.

For experiments of this kind, the bell of the medusa has become,
through the work of Romanes (1885), a classical object. Separating
the margin of the bell, containing the chief portion of the nervous sys-
tem, from the central part, has been a favorite experiment. Romanes
found that in the Hydromeduse the margin continues to beat rhythmi-
cally, while the centre usually ceases its spontaneous movement. But

228 BEHAVIOR OF THE LOWER ORGANISMS

this was not due to any actual inability of the centre to initiate move-
ment, for Romanes found that when it was stimulated in various ways,
it contracts rhythmically. This occurred in the centre of the bell of
Sarsia when placed in certain chemicals, notably in weak acids, and
in a glycerine solution (Romanes, 1885, pp. 190-197). Rhythmical
contractions have likewise been observed by Loeb (1900 @) in the iso-
lated centre of Gonionemus when placed in a pure solution of sodium
chloride. Thus it is clear that not only the margin, containing the
greater part of the nervous system, but also the centre of the bell, has
the power of contracting rhythmically.

These and many other experiments have shown that each part of
the body has in the ccelenterates certain characteristic ways of reacting
to stimuli, and that it may react in these ways even when separated
from the rest of the body. Its reactions may be determined within
itself. But from this the conclusion cannot be drawn that the behavior
of these animals consists entirely of the separate and independent re-
actions of these parts to external stimuli. While each part may react
independently, each may also react with reference to influences coming
from other parts of the body. Thus, the tentacles may react, not only
to external stimuli directly impinging upon them, but also, in many
coelenterates at least, to stimuli that are transmitted from other parts.
A strong stimulus on the body or on a single tentacle causes a contrac-
tion of many tentacles. In some cases this contraction of the other
tentacles appears to be due to a direct spreading of the muscular con-
-traction. One fibre pulls on another, setting it in action, until the pull
reaches the base of the tentacle. This pull then acts as a direct stimu-
lus, causing the tentacle to contract, in the same way that would occur
if it were mechanically stimulated from outside. This is the way in
which Torrey conceives of the matter in Sagartia. If this is the correct
explanation, there is of course nothing comparable to nervous trans-
mission — passage of a wave of stimulation independently of a wave of
contraction — in these cases.

In Atpiasia annulata, on the other hand, a light stimulus on the tip
of one of the long tentacles induces a sudden quick contraction of the
entire body. This contraction appears to the eye to take place over
the entire body at once, and it is so rapid as to suggest strongly the opera-
tion of a conducting nervous system. The well-known experiments of
Romanes (1885, p. 76) demonstrated completely that in meduse there
is such a wave of stimulation independent of a wave of contraction,
and that this wave of stimulation coming from other parts of the body
causes the tentacles to contract. By cutting off the margin of Aurelia
in the form of a long strip and stimulating one end, he could cause a

BEHAVIOR OF C@LENTERATA 229

wave of stimulation to pass to the opposite end. This wave of stimu-
‘lation was followed, if the stimulus was intense, by a wave of contrac-
tion; if the stimulus was weak, the wave of stimulation passed alone.
This wave caused the tentacles along the margin to contract as it
‘reached them.

Furthermore, we have seen above that the reaction of the tentacles
or of other parts of the body to a given stimulus depends upon the gen-
eral physiological state of the body, as determined by the progress of
metabolism. Certain tentacles may, through the activity of totally
different tentacles, in another region of the body, in supplying material
for the metabolic processes, come to react to a given stimulus in a man-
ner entirely different from their former reactions.

The tentacles are therefore not to be compared. exclusively to in-
dependent organisms associated in a group, but they form parts of a
unified organism. While they may react when isolated, they react also
under the influence of other parts of the body. We have of course the
same condition of affairs in the muscles and various other organs of
vertebrates. They may react when isolated, but, like the tentacles
of the medusa, they likewise react to influences coming from other parts
of the organism.

The same is true for the manubrium and for other parts of the body.
While the isolated manubrium of Gonionemus may react by bending
toward food, it shows the same reaction when certain of the tentacles
are stimulated by an object moving rapidly across them. The varied
reactions of the manubrium to influences affecting other parts of the body
are shown most clearly in the experiments of Romanes described on
page 201. In Hydra, when the tentacles have seized food, the mouth
often begins to open long before the food has reached it. In Metridium,
according to Parker, when the tentacles are touched by food, the
cesophagus frequently shows peristaltic contractions, and the sphincter of
the mouth closes. It is clear that there is a definite coérdination and
unity in the behavior, brought about by a transmission of stimuli from
one part of the body to another. The difference between these organisms
and higher animals is in this respect only one of degree. In the ccelen-
terates a large share of the behavior is due to the independent reactions
of the different organs to the external stimuli, and the transmission of
influences from one part of the body to another takes place slowly and
without such precision as we find in higher animals. .

The part played by the nervous system in unifying the body we
need not take up here, as it has been thoroughly analyzed in the brill-
iant work of Romanes (1885), and has been further discussed by Loeb
(1900). The essential conclusion to be drawn from the experimental

230 BEHAVIOR OF THE LOWER ORGANISMS

results seems to be as follows: The nervous system forms a region in
which the physiological changes resulting in activity take place more
readily and rapidly than in other parts of the protoplasm. These
changes occur in the nervous system more readily both as a result of the
action of external stimuli, and under the influence of changes in neigh-
boring parts of the body. Hence parts containing the nervous system
are more sensitive to external stimulation than other parts of the body,
and they serve to transmit stimulation more readily. . Furthermore,
the spontaneous changes occurring in the protoplasm, which result in
the production of rhythmical contractions, are more pronounced and
rapid in the nervous system than elsewhere, so that the rhythmical
contractions usually begin in parts containing nerve cells. But the
difference between nerve cells and other cells is only quantitative in
character. The peculiar properties of the nerve cells are properties of
protoplasm in general, but somewhat accentuated,

tz. Some GENERAL FEATURES OF BEHAVIOR IN CQ@:LENTERATES

Comparing the behavior of this low group of multicellular animals
with that of the Protozoa, we find no radical difference between the two.
In the ccelenterates there are certain cells — the nerve cells — in which
the physiological changes accompanying and conditioning behavior
are specially pronounced, but this produces no essential difference in
the character of the behavior itself. As in the Protozoa, so here, we
find behavior based largely on the process of performing continued or
varied movements which subject the organism to different conditions
of the environment, with selection of some and rejection of others.
We find the same changes in behavior under a continued intense stimu-
lus, determined by changes in the physiological condition of the animal.
We find at the same time many reaction movements of a fixed character,
dependent largely on the structure of the organism, as we do in bacteria
and infusoria. Many of these specific responses to specific stimuli
are so definitely adapted to the precise conditions under which the
organism lives that we can hardly resist the conclusion that they have
been developed in some way under the influence of these conditions,
as a result of the fact that they are beneficial to the organism. Such, for
example, is the quick though complicated grasping and feeding reaction
by which Gonionemus responds to a moving object. Possibly such
determinate reactions have arisen through fixation of movements which
were originally reached by a process of trial, —a possibility to which
we shall return in our general analysis of behavior.

In the Coelenterata we find also, as in Amceba, a certain number of

BEHAVIOR OF C@LENTERATA 231

responses due to the simple, direct reaction (by contraction) of the part
affected by a local stimulus. Where such simple and perhaps primi-
tive reactions are advantageous to the organism, they are preserved as
important factors in behavior, as in the negative reactions of medusez.
Where they are not advantageous to the organism, they are replaced,
supplemented, or followed by more complicated reactions, so that they
form a comparatively unimportant feature in the behavior of most of
these animals.

In ccelenterates we find.the same dependence of behavior on the
physiological state of the organism that we found so marked in Pro-
tozoa. ‘The same organism does not react always in the same way to
the same external conditions. In the preserit group the dependence of
behavior on the progress of the internal physiological processes, par-
ticularly those of metabolism, stands out strongly. The animal in which
material for the metabolic processes is abundant differs radically in its
behavior from the hungry specimen. The reaction to a given stimulus
depends not alone on the anatomical structure of the animal and the
nature of the stimulus, but also upon the way the internal processes
are taking place. We cannot predict how an animal will react to a
given condition unless we know the state of its internal physiological
processes, and often whether a positive or negative reaction will help
or hinder the normal course of these processes. ‘The external processes
of behavior are an outgrowth and continuation of the.internal processes.

The state of the organism as regards its metabolic processes seems
indeed the most important determining factor in its behavior. Certain
internal metabolic states drive the animal, without the action of any
external agent, to the performance of long trains of activity, of exactly
the same character as may also be induced by external stimulation.
The state of the metabolic processes likewise determines the general
nature and the details of the reactions to external stimuli. It decides
whether Hydra shall creep upward to the surface and toward the light,
or shall sink to the bottom; how it shall react to chemicals and to solid
objects; whether it shall remain quiet in a certain position, or shall
reverse this position and undertake a laborious tour of exploration. It
decides whether the sea anemone shall react to indifferent bodies, and
to food, by the long and complex “food reaction” or the equally long
and complex “rejecting reaction.’”’ It determines whether Cerianthus
shall remain quietly in its tube in the sand, or shall seek a new abode.
Innumerable details of behavior are determined in the ccelenterates
by this factor.

The same dependence of behavior on the metabolic processes of the
organism we have seen in the Protozoa, and especially in the bacteria.

232 BEHAVIOR OF THE LOWER ORGANISMS

Here, however, the change of behavior of a given individual with a
change in these processes needs further investigation; this has been
experimentally demonstrated only with reference to respiratory pro-
cesses in certain green organisms. In higher animals the dependence
of the behavior on the state of metabolism is of course most evident.

This dependence of the reaction to stimuli on the relation of external
conditions to internal processes is a fact of capital importance, which
may furnish us a key to many phenomena that are obscure from other
standpoints. The processes of metabolism are not the only ones occur-
ring in organisms, and the relation of external conditions to other
internal processes may equally determine behavior. This is perhaps
the most fundamental principle for the understanding of the behavior
of organisms.

Of a character differing from those just considered are certain
other factors which modify behavior in the ccelenterates. Past stimuli
received and past reactions given are, as in the Protozoa, important
determining factors in present behavior; they may cause either the
cessation of reaction to a given stimulus, or a complete change in the
character of the reaction. Certain simple conditions produce a ten-
dency in the organism to perform more readily anact previously performed
(p. 206). The internal state of the organism may be changed in most
varied ways, giving rise to corresponding changes in behavior. These
facts give behavior great complexity, as well as great regulative value,
even in so low a group as the one now under consideration.

LITERATURE XI
BEHAVIOR OF CCELENTERATA

A. Behavior of Hydra: WAGNER, 1905; WILSON, 1891; MARSHALL, 1882;
PEARL, 1901 ; MAST, 1903; TREMBLEY, 1744.

B. Behavior of sea anemones: LOEB, 1891, 1895, 1900; NAGEL, 1892, 1894,
1894 @; PARKER, 1896, 1905, 1905 @; TORREY, 1904; JENNINGS, 1905 @; ALLA-
BACH, 1905; CARLGREN, 1905; BURGER, 1905.

C. Behavior of hydroids: TORREY, Ig04 a.

D. Behavior of jellyfish: ROMANES, 1885; YERKES, 1902 @, 1902 4, 1903,
1904; PERKINS, 1903; BANCROFT, 1904; LOEB, 1900, 1900 a.

CHAPTER XII

GENERAL FEATURES OF BEHAVIOR IN OTHER LOWER
METAZOA

THE foregoing chapters attempt to give a connected systematic
account of behavior in the Protozoa and the Ceelenterata. These
may serve as types of the lower organisms. The necessary spatial
limits of the present work render impossible a similar treatment of
other groups. We must content ourselves therefore with a survey of
some of the main features of behavior in some other invertebrates.
We shall take into consideration chiefly the lower groups.

1. DEFINITE REACTION Forms (‘‘REFLEXES’’)

In the action systems of most organisms we find certain well-defined
reaction forms, or what are often known as reflexes,’ which make up a
large proportion of the behavior. In the groups we have thus far con-
sidered, such definite reaction types are seen in the avoiding reactions
of infusoria, the definite contractions occurring in response to stimuli
in the Protozoa and Ccelenterata, the bending of the tentacles toward
the mouth when stimulated by food, in the hydroids and sea anemones,
and in many other features of the behavior. It is true, as we have
seen, that even these so-called reflexes are usually variable when studied
in detail, and their occurrence and combination depend upon a mul-
tiplicity of internal as well as external conditions. Yet certain elements
of behavior do occur in accordance with a definite type, and this fact
is one of much importance. In some lower animals behavior is largely
made up of such definite reaction forms. This fact has assumed an
overshadowing importance in much recent work on behavior; investi-
gation has taken largely the form of a search for precisely definable
reflexes and tropisms, and for conditions under which they occur in the
typical way, while other factors in the behavior have been neglected.
Since these matters have been so much dwelt upon, we need not take
them up in great detail in the present work.

The best-known case of behavior made up largely of such definite

1 The use of this term will be discussed later.
233

234 BEHAVIOR OF THE LOWER ORGANISMS

reaction forms is that of the sea urchin, as studied by v. Uexkiill (1897,
1897 4a, 1899, 1900, 1900a). The sea urchin differs from most lower
animals in bearing large numbers of motor organs
scattered over its entire surface. Most prominent of
these are the spines, which are movable, and may be
used as legs, or as means of defence. Among the
spines are certain peculiar jawlike organs known as
pedicellarie (Fig. 133), each borne on a movable stalk.
These jaws frequently open and close, seizing foreign
objects. The surface of the body between the spines
and pedicellarie is covered with cilia. Finally, the
body bears five double rows of tube feet, — fleshy
tubular suckers, protruded through rows of holes in

- the shell. These are important organs of prehension
of ag te and locomotion. All these different sets of organs
from a sea urchin. are interconnected by a network of nerves, one set
After v. Uexkiill. tying on the outer surface of the shell, another on the
inner surface. These nerves connect with the five radial ‘nerve trunks,
which unite to form a ring surrounding the mouth.

V. Uexkiill finds that each of these organs (omitting the cilia) has
a number of definite reactions or reflexes, which it performs in response
to definite stimuli. In these reactions each organ may act as an inde-
pendent individual. Ifa piece of the shell bearing but a single spine or
pedicellaria is removed, this organ reacts to external stimuli in essen-
tially the same way as when connected with the entire animal. These
reflexes change with different intensities and qualities of stimuli, and
with certain other conditions, and they are different in diverse sorts of
pedicellariz. But each reflex has a very definite character. Thus the
sea urchin appears to be made up of a colony of almost independent
structures. Each of these structures has reactions of such a character
that they perform certain functions that are useful in the life economy
of the animal.

Yet these organs are not entirely independent. They are connected
by the nervous network in certain definite ways, so that when one of
them performs a certain action, others may receive a transmitted stimu-
lus, and may perform the same or a differing action. That is, each
organ may receive stimuli not only from the outer world, but also,
through the nerves, from other parts of the body. These interconnec-
tions are of such a character that they cause the various organs to work
in harmony, usually assisting to perform certain necessary functions.

Thus, if débris falls upon the sea urchin, the pedicellariz seize it,
_ break it into bits, and with the aid of the spines and the cilia remove

BEHAVIOR IN LOWER METAZOA 235,

it from the body. Small animals coming in contact with the sea urchin
are seized by the pedicellariz and held, till they are grasped by the slow-
moving tube feet and spines, and by them carried to the mouth and eaten.
When the sea urchin is attacked by an enemy, the spines all bend
toward the region of attack, presenting a serried array of sharp points to
the advancing enemy. In some species this occurs even when a shadow
falls upon the animal. The spines present their points to the shaded
side, thus arranging for an effective defence in case the animal which
has cast the shadow shall advance to an attack. In some sea urchins,
poisonous pedicellariz seize an enemy, usually causing a quick retreat.
Further, when the animal is severely stimulated from one side, the
reflexes of the spines are so arranged as to carry the animal in the op-
posite direction. When attacked, the animal is thus effectively defended,
while at the same time it flees.

V. Uexkiill emphasizes the independence of these organs, the defi-
nite character of their reflexes, and the definiteness of the interconnections
between them. These qualities give the characteristic stamp to the
behavior of the sea urchin. According to v. Uexkiill, this animal is
a “‘republic of reflexes.” Every reflex is of the same rank, and is in-
dependent of the others, save for the definite connections that we have
mentioned. There is nothing like a central unity controlling the re-
flexes, according to v. Uexkiill. The sea urchin, he holds, is a bundle
of independent organs, and it is only through the arrangement of these
organs that a seemingly unified action is produced. ‘‘It is only by the
synchronous course of the different reflexes that there is simulated a
unified action, which really does not exist. It is not that the action is
unified, but the movements. are ordered, 7.e. the course of the different
reflexes is not the result of a common impulse, but the separate reflex
arcs are so constituted and so put together that the simultaneous but
independent course of the reflexes in response to an outer stimulus
produces a definite general action, just as in animals in which a common
centre produces the action” (1899, p. 390). The difference between
the behavior of the sea urchin and that of higher animals is concretely
expressed by v. Uexkiill in the statement that when a dog runs the
animal moves its legs; when the sea urchin runs the legs (spines) move
the animal. ,

Yet the fixity of these reactions is by no means absolute, even in the
sea urchin. As we shall see in the next section, v. Uexkiill discovered
a number of definite laws in accordance with which they change, and
there is positive evidence of still other modifying factors not easily
formulated.

In scarcely any other group of lower animals does there appear to

236 BEHAVIOR OF THE LOWER ORGANISMS

be such a multiplicity of these definite units of reaction as in the sea
urchin. In the starfish the extension and withdrawal of the tube feet,
and the extrusion and withdrawal of the stomach in feeding, may be
considered examples. In free-swimming rotifers we find an avoiding re-
action similar in all essentials to that of the ciliate infusoria, the animals
when stimulated turning toward a structurally defined side. There
is the same variability in this reaction that we find in the infusoria. In
planarians, the earthworm, and many other worms, reactions of a fairly
well-defined character are seen in the turning of the head toward certain
stimuli and away from others. These reactions play a large part in
the behavior of Planaria, according to Pearl (1903). Weak stimuli of
all sorts affecting one side of the body cause the positive turning ; stronger
ones, the negative turning.

Such reactions often depend closely on the localization of the stimu-
lus. This may be illustrated from the behavior of the flatworm just
mentioned. A weak stimulus at the side of the head, near the anterior
tip, causes the head to turn only a little toward the side touched. If
the stimulus is farther back, the turning is greater. In each case the
turning is so regulated with reference to the point stimulated as to direct
the animal very accurately toward the region from which the stimulus
came; this aids it much in finding food. If something touches the flat-
worm lightly at the middle of the upper surface of the head, the reaction
is much modified. The head is sharply raised and twisted, so as to
direct the anterior tip toward the stimulating object, and in such a way
that the ventral surface will first come in contact with this object as the
animal moves forward. Similar regulatory changes occur in the nega-
tive reaction. A strong stimulus at the side of the anterior end causes
a quick turning away. A similar stimulus at one side behind the middle
causes no turning away, but only a movement forward. At intermedi-
ate regions there is a combination of the two reactions, the animal glid-
ing forward and at the same time turning away. The farther back the
stimulus is given the greater is the tendency to react by moving forward
in place of turning away. This change of reaction with a change in
the point stimulated is of course regulatory. An intense stimulus at
the anterior end is best avoided by turning away, while one near the
posterior end is most easily escaped by moving rapidly forward.

In most animals there are found a certain number of these relatively
fixed reaction types which are determined by the usual conditions of
existence, — gravity, light, temperature changes, contact with solids,
etc. We have examined a considerable number of these in the Protozoa
and Ccelenterata. In such reactions the organism often turns or bends
directly toward or away from the source of stimulation, as in the posi-

BEHAVIOR IN LOWER METAZOA 237

tive and negative reactions of the flatworm. Reactions of this charac-
ter are commonly spoken of as ¢tropisms. In the higher animals and
man behavior is, of course, largely determined by the same factors. As
we have seen in previous chapters and shall find in the following sec-
tions of the present one, in neither lower nor higher animals are the
reactions with reference to the general forces of nature of a completely
fixed and invariable character."

In more complex animals than those considered in the present vol-
ume, definite reaction forms are often combined into complex trains of
action which are known as instincts.. Recent work has shown that in
these instincts there is by no means that absolute fixity of behavior that
was formerly assumed to exist. A detailed treatment of this matter
would take us outside the field of the present work.

In the highest animals and man, definite reaction forms, which may
take place in certain organs independently of the rest of the body, are
of course found as abundantly as in lower organisms. Such reactions
are seen in the reflexes of muscles, etc., which persist even after the
muscle has been removed from the body. There is no difference in
principle along this line between higher and lower animals. The
former possess a much larger number of such definite types of move-
ment, and these doubtless make up fully as large a portion of behavior
as in the lower animals.

There are some accounts of behavior in various lower animals in
which only these definite reaction forms are described and only those
conditions are dealt with in which these appear in the typical way.
Such accounts have given rise to a widespread impression that behavior
in the lower animals differs from that of higher forms in that it is of a
fixed, stereotyped character, occurring invariably in the same way under
the same external conditions. This impression is in a high degree
erroneous. These definable reaction forms are usually in themselves
variable within wide limits, as exemplified in the avoiding reaction of
infusoria. But even if this were not true, the criteria for judging as to
the fixity or modifiability of behavior are to be derived from the study
of the conditions that induce reaction, that determine which of several
possible reactions shall occur, and that determine the order and combina-
tion of reactions. Such a study shows that in lower as well as in higher
animals varied internal conditions and changes are of the greatest im-
portance in determining behavior, the animal by no means behaving
always in the same way under the same external conditions. With this
aspect of the matter we shall deal in the two following sections.

1 See, for example, the section on reactions to gravity in coelenterates, Chapter XI.

238 BEHAVIOR OF THE LOWER ORGANISMS

2. REACTION BY VARIED MOVEMENTS, WITH SELECTION FROM THE
RESULTING CONDITIONS

In the foregoing section we have dealt with the fact that stimulation
often causes the performance of actions that are of a definite, typical
character, such as are often called reflexes. But this by no means ex-
hausts the problem of behavior, as our account of the matter in unicel-
lular animals and in Ccelenterata has shown us. Indeed, we find it not
to be the rule that an animal when stimulated performs a single definite
movement, then returns to its original state. On the contrary, stimula-
tion is usually followed by varied movements, and the animal may con-
tinue active long after the external agent has ceased to impinge upon it.
The continued varied: movements subject the organism successively to
many different conditions, external and internal. In one of these con-
ditions the animal remains through a cessation of the changes in activ-
ity. It may thus be said to select certain conditions through the pro-
duction under stimulation of varied movements. We have seen many
examples of this type of behavior in the groups thus far considered.

Behavior of this character is very general in lower animals. We
shall in the present section give a number of examples, taken from
diverse classes of invertebrates.

As we have seen, the echinoderms furnish perhaps the best examples
of organisms in which the behavior is made up largely of more or less
independent “reflexes.” Yet in the same group we find that much of
the behavior is of the type now under consideration. There is, of course,
no opposition between the two, the different “reflexes” forming the
variables out of which behavior of the present sort is made up. The
pedicellariz of the sea urchin have, as we have seen, a number of these
definite reflexes. When the entire animal is suddenly and strongly
stimulated, by mechanical shock, by a chemical, or by light, the pedi-
cellarie respond, not by a single definite reflex, but by beginning to
move about in all directions (v. Uexkiill). They seem to feel and
scrape the entire surface of the body, seizing anything with which they
come in contact, and this behavior may continue for an hour or more
after stimulation has ceased. Similar effects are often produced in the
spines by a general stimulus. They wave about, their tips describing
circles, and this may continue for a long time. Such reactions are seen
also in the tube feet. When the sea urchin or starfish is suspended in
the water or is placed on its back, the tube feet extend and wave back
and forth, as if searching for something to which they might attach
themselves.

On a more extensive scale, the “righting” reaction of the starfish is

BEHAVIOR IN LOWER METAZOA 239

a notable example of behavior that is not stereotyped, but is flexible and
variable. The usual course of this reaction is as follows: After the
starfish has been placed on its back, it extends its tube feet and moves
them about in all directions. At the same time the tips of the arms be-
come twisted, so that some of the tube feet are directed downward. In
this way, after a time, some of the feet become attached to the bottom.
These begin to pull on the arm to which they belong, turning it farther
over and bringing other tube feet into contact with the bottom; these
now assist in the process. If two or three adjacent rays become thus
attached, the other rays cease their searching, twisting movements, and
allow themselves to be turned over by the activities of the tube feet. of
the attached rays. If two or more opposite rays become attached to
the bottom in such a way that they oppose each other, then one releases
its hold, and allows the turning to be accomplished by the opposing rays.
It is evident that the reaction is an example of the performance of varied
movements under stimulation, with selection from the conditions re-
sulting from these movements. Certain features in this reaction are of
special interest. At first all the tube feet and rays try to find an attach-
ment. When certain ones have succeeded, this is in some way recog-
nized by those parts whose action would oppose the movement, for these
cease their attempts, or even release the hold already attained. In some
way the physiological state corresponding to “success” in -certain rays
is transmitted to the other rays, and they change their behavior accord-
ingly.

Variability and flexibility are the essence of such behavior. This
is well illustrated by study of repetitions of the righting reaction in the
starfish. It is by no means always the same arm or combination of
arms that initiates and finally brings about the turning. The essential
point is to get started in some way, then to continue on the basis of the
start made. Preyer (1886) studied this behavior in the starfish with
great care. He says: “ Neither in one [species] nor the other is the method
of turning always the same. I have likewise seen Aséerias glacialis,
which was several times in succession turned on its back without change
in the outer conditions, right itself sometimes in one manner, sometimes
in another. The spirals of the twisted arms do not work each time in
corresponding directions, but at first the neighboring arms often oppose
each other. But soon the correction takes place, in that the attached
feet stop those that are disturbing the turning, and the wrongly twisted
radii straighten out again... . The variability of form in starfish
that are righting themselves is great, and no species rights itself in only
one way. ... But here, too, it is true that no Astropecten rights itself
twice in succession in exactly the same way. An adaptation to the sur-

240 BEHAVIOR OF THE LOWER ORGANISMS

face of attachment always occurs, and according as this is convex, con-
cave, smooth, rough, or inclined, is the turning process made easier or
more difficult, and brought about in this manner or that” (1886, pp. 107—
108). Sometimes the animal turns a somersault; sometimes it extends
all its arms upward, taking the “tulip” form and toppling over on one
side — and so on through many variations. |

Even the main features of the typical reaction,may be omitted or
changed, the turning taking place by means quite different from the
usual ones. Thus, Astropecten aurantiacus usually rights itself by
means of its tube feet, but sometimes turns without using the tube feet
at all. Lying on its back, it lifts the central disk high, resting on the
tips of three or four of the arms. Then it turns two of the arms under,
while lifting the others upward, so that it now falls with ventral side
down. During this action the tube feet are moved about in a lively
way, and when the turning is nearly completed the tube feet of the
upper radii which are approaching the substratum are pushed far out,
as if preparatory to meeting the bottom.

When a portion of the feet were prevented from acting, by subjecting
them to alcohol or other drugs, Preyer found that the starfish righted
itself by means of the remaining ones, and by bending and twisting its
arms. Pieces of the arms may right themselves, and this again occurs
in many different ways.

The thorough study of the movements and reactions of the starfish
made by Preyer (1886) shows that the righting reaction is typical of the
entire behavior. If the starfish is suspended just below the surface of
the water with ventral side up, by threads attached to the tips of its
arms, it performs varied movements, until in the course of time it turns
over, just as in the usual righting reaction. If a short rubber tube was
slipped over one of the arms of a brittle star, to its base, Preyer found
that this caused the animal to perform many varied movements, till by
one of them the tube was removed. Sometimes the animal merely
moved rapidly forward, dragging the arm bearing the tube behind it
till the tube was scraped off. Sometimes the animal placed one or two
of the other arms against the tube and forced it off. In other cases the
covered arm was dropped from the body (as often happens in brittle
stars). Again, sometimes the arm bearing the tube was lifted and
waved back and forth, till the tube was in this way displaced. Thus
Preyer observed five different ways in which the tube was finally re-
moved; as he remarks, ‘“‘If one method does not help, another is used.”
It may, of course, be maintained that in all these cases the removal of
the tube was in a sense accidental. But this is precisely the essential
point in much of the behavior of lower organisms. When stimulated

BEHAVIOR IN LOWER METAZOA 241

they perform varied movements, till one of these “accidentally” re-
moves the source of stimulation. How this may develop into more
directly regulatory reactions we shall consider in the next section.

The same qualities are shown in certain experiments of Preyer in
which he attempted to confine the starfish by means of large, flat-headed
pins. These were placed in the angles between the rays, close against
the disk, and driven into the board on which the starfish lay. They
thus held it down without injury. The starfish in the course of time
escapes from the pins, but only after much effort. The animals try
successively various methods, “‘now they seek to force themselves through,
now to climb over the top, now to push through by turning on one side.”
In scarcely any two cases does the process of escape occur in the same
way, according to Preyer. The behavior is as far as possible from that
of invariable reflexes always occurring in the same way under the same
external conditions.

One further point mentioned by Preyer is of great interest. He says
that when the experiment is repeated with the same individual, the
time required for escape becomes less. ‘The number of useless move-
ments, ‘‘superfluous twistings, feelings about, and forward and back-
ward motions,” becomes less the oftener the individual has been placed
in such a situation. If this is true, we have in so low an animal as the
starfish regulation through the selection of conditions produced by
varied movements passing into a more directly regulatory action; in
other words, what is commonly called in higher animals intelligence.
There seems to be no reason for doubting Preyer’s observations on this
point, but on account of their great importance they should be repeated
and verified or refuted.

Many other illustrations of behavior of the general character set
forth above could be presented from the valuable work of Preyer (1886).
It has become the fashion to neglect and even speak slightingly of the
work of Preyer on the behavior of the starfish. This seems to be due
to the tendency observable in recent scientific literature to represent all
such matters as extremely simple and reducible to separate well-known
mechanical factors, and to avoid all experiments tending to reveal the
fallacy of this view. Preyer was not afraid to open his eyes by properly
designed analytical experiments to the complexity and regulatory charac-
ter of the behavior. Such thorough and detailed studies of animal be-
_ havior as that of Preyer on the starfish are rare at the present time; his
work stands in this respect in most refreshing contrast with some of the
superficial work recently put forth. The excellent work of Romanes
(1885) had already, before Preyer, brought out many examples of the
style of behavior we have illustrated above.

R

242 BEHAVIOR OF THE LOWER ORGANISMS

In many free-swimming Rotifera the chief methods of movement and
reaction are similar even in details to those of the free-swimming infusoria,
which we have already described. Like the infusoria,

these rotifers swim by means of cilia, revolve on the
long axis, and swerve toward one side (usually dor-
sal), as they progress. The cilia produce a current
passing from in front to the mouth and ventral side,
thus allowing the animals to test the conditions in
advance. To most effective stimuli these rotifers
react, as do the infusoria, by swerving more than
usual toward one side, — usually the dorsal side.
Thus the spiral becomes much wider, and the ani-
mals are pointed successively in many different direc-
tions and subjected to many different conditions. In
time they may thus reach conditions which relieve
them of the action of the stimulating agent. There-
upon the reaction ceases, so that the animals con-
tinue in the direction which has thus been reached.
All the general features of the reactions are essen-
tially like those of infusoria, so that we need not
enter into details. The reactions to mechanical stim-
uli, to chemicals, to heat and cold, to light, and to
electricity are known to occur in the way just

SA fos ries Pla- sketched, in a number of species. Orientation to

a, dors view. ~. z
After Woodworth. light and to the electric current takes place in the
same way as the orientation to light in Euglena and Stentor. It is inter-
esting to observe that in the Rotifera, owing to the concentration of the
cilia at one end of the animal, there is no such incoherence and lack of
coérdination in the reaction to the constant electric current, as is
found in infusoria. The rotifer (Anurea cochlearis) becomes oriented
with anterior end to the cathode by the same method as in reactions
to light and other agents.

In many rotifers the reaction plan just described forms only one
feature of the activities, so that the behavior, taken all together, may be
exceedingly complex. There is much opportunity for further study of
the reactions of this group. But so far as known, much of the behavior
may be expressed as follows: When stimulated, the animals perform
continued and varied movements, the variations often taking place in a
systematic way. ‘These movements necessarily subject the animals to
varied conditions, one of which is finally selected, through the fact that
it removes the cause of stimulation.

Much of the behavior of the flatworm Planaria (Fig. 134), as studied

BEHAVIOR IN LOWER METAZOA 243

by Pearl (1903), may be summed up under the same formula set forth
in the preceding paragraph. Varied movements which subject the ani-
mal to many different conditions, are seen even in the unstimulated
specimen. As the flatworm glides along by means of its cilia, the head
is held upward (Fig. 135) and moved frequently from side to side, while
its margins wave up and B AC

down, and are extended
and contracted. The flat-
worm thus seems to “feel
its way” with its head.
Sometimes these fecling Fic. 135.— Side view of moving Planaria. After
movements become much Pearl. A, body; B, mucus; C, cilia; D, substratum.
accentuated, the animal almost or quite stopping, then raising the
whole anterior part of the body and waving it about in the water.
These movements of course serve to test the environment on each side;
in other words, they subject the sensitive anterior end to varied con-
ditions. :

The testing movements are specially marked under certain condi-
tions. When the active planarian is about to come to rest, it stops and
moves the anterior end from side to side, touching any object that may
be found in the neighborhood. After thus thoroughly testing the sur-
roundings, the muscles relax and the animal comes to rest. When later
the animal resumes its active progression, this begins again with the
testing movements of the head.

The same testing movements are seen under various sorts of stimu-
lation. On coming to a solid body, the flatworm moves the head
about over its surface. If it turns out to be some-
thing fit for food, the animal now feeds upon it, other-
wise it moves away again. If while a number of
specimens of Planaria are moving in a certain direc-
tion, the direction of the light is changed so as to fall
upon their anterior ends, they usually turn the head
from side to side two or three times, then follow up
one of these movements by turning the body till it is
finally directed away from the light. These testing
movements are also seen when the animal begins to

Wop: 448) —-'Re- dry, and when the water is heated; the worm gives the
action of Planaria to impression that it is seeking about for other conditions.
drying. After Pearl. Other features of the reactions to drying and to
temperature changes are of interest from our present standpoint. If
the planarian is laid on a glass plate, as soon as the tendency to dry
becomes evident the worm curls up closely and thrusts the head under

244 BEHAVIOR OF THE LOWER ORGANISMS

the body (Fig. 136). In this way the exposed surface of the body is
made as small as possible, and the sensitive head especially is kept from
drying. At intervals the animal straightens out, extends its head as
far as possible, and waves it from side to side. If in this way it finds
water, it of course moves into it. If it does not find water, it curls up
again. After a time, if the drying becomes more decided, the animal
attempts to crawl backward. Under natural conditions drying will
usually take place at the edge of a pool, and. this backward movement
carries the animal again into the water. All together, the reaction to
drying is not simple and stereotyped, but involves the successive per-
formance of many different activities.

In responses to heat or cold we find a similar train of activities. If
the gliding Planaria comes to a region of considerably higher or lower
temperature, it waves its head back
|} and forth several times, apparently
till it has determined the direction
which leads back to the usual
temperature, then turns and moves
in that direction. Responses of
this character usually take place
several times before the animal is
completely directed toward the re-
gion of optimum temperature (see
Fig. 137). If the temperature of
the water is slowly raised in a
uniform manner, so that all parts
22° of the body are similarly affected,
| then a series of reactions occurs.

First the animals become more

Fic. 137. — Behavior of the flatworm in ap- active, gliding about rapidly, ex-
pouring tenet end ofa tourh; Thelines tending the head, and turning it
marked by a round spot, the animal stopped and toward one side or the other. The
waved its head to and fro, finally following up hehavior resembles that of speci-
one of the trial movements. The figures at these ee
points show the number of trial movements that Mens showing the “positive” re-
Were ekedeyits each cane.’ After Meat, action to weak stimuli. As the
temperature rises, the animal begins to contract at intervals, and to turn
the head frequently and strongly from side to side, making little prog-
ress in advance. The behavior has now the characteristics of the
“negative” reaction. As the temperature rises further, the turning
ceases, and the animal begins to make rapid, violent contractions, such
as occur in “crawling,” under other violent stimuli. Later the animal
twists its body, as occurs in its righting reaction when placed on its

32°
2

BEHAVIOR IN. LOWER METAZOA — 245

back; it thus forms a spiral of two turns. Finally it behaves in a
manner somewhat similar to that shown when it dries. It rolls the .
two ends under the body, arching the dorsal surface. In this position
the animal rolls over on its back and dies.

Thus under a single unlocalized stimulus of gradually increasing in-
tensity, the behavior of the organism passes through a series of stages,
closely resembling the reactions given under most diverse conditions.
As Mast (1903), to whom these observations are due, expresses it, “the
general impression is given that as the thermal stimulus increases, the
animal tries, in a sort of ‘hit-or-miss’ way, every reaction which it has
at command in order to get rid of the stimulation.”

The “righting reaction” of the flatworm is another example of a
response that is not stereotyped in character, but varies greatly. If the
animal is turned on its back, it quickly rights itself again. This usually
occurs as follows. The animal twists itself into a spiral (Fig. 138, A),

Fic. 138. — Righting reactions in the flatworm. After Pearl. A, reaction of entire worm.
B, righting reaction of short piece from anterior end of worm. a, 8, c, d, e, f, successive steps in
the process. C, righting reaction of triangular pieces. @, manner in which the piece is cut.
b, a small portion of the thin edge turns so as to bring the ventral surface in contact with the
bottom. c, d, this turning increases; by a continuation of the process the whole piece is finally
righted. e, /, cross sections through the pieces while turning.

thus causing the ventral surface of the head to face the bottom, where
it attaches itself. Then the worm creeps forward, bringing successively
more and more of its ventral surface in contact with the bottom, pro-
ceeding toward the rear. Thus the spiral is unwound, so that after the
animal has traversed a short distance, the entire ventral surface is in
contact with the bottom, as usual.

But the righting reaction may take place in quite a different way.
Pearl (1903) cut the planarian into pieces of such form that it could no

246 BEHAVIOR OF THE LOWER ORGANISMS

longer twist itself into a spiral. Then some portion of the ventral sur-
face was brought by other means into contact with the bottom, and
from this point the remainder of the surface was pulled into contact. In
small strips from the head region, the posterior ends are turned under,
bringing the ventral side at this point against the bottom, then by pull-
ing from this point, the entire piece was turned over endwise (Fig. 138,
B). In triangular pieces from the middle of the animal, one edge was
turned under, then the remainder righted from this region, by pulling
the rest of the piece over (Fig. 138, C). These modifications bring out
the essentially adaptive character of the behavior. The essential point
seems to be, to get some portion of the ventral surface, by any means
whatever, into contact with the substratum, then by working out from
this point, to bring the whole ventral surface into attachment.

From certain points of view the whole behavior of the flatworm may
be considered a process of testing all sorts of conditions, retaining some
and rejecting others. As we have seen in the section which precedes
the present one, the positive reactions of this animal are not due to any
specific qualities of stimulation. On the contrary, the animal turns
toward weak stimuli of all sorts. Solid bodies, whether fit for food or
not, chemicals of all sorts, including the injurious as well as the bene-
ficial, heat, and cold, all induce, when acting but slightly on one side,
a turning toward the source of stimulation. The flatworm may thus
be said to investigate every slight change occurring in its surroundings.
On reaching a region where the agent in question acts more intensely,
the positive reaction may either continue or be transformed into a nega-
tive one. Thus the turning toward food is not due to the specific quali-
ties which make the substance in question fit for food, but is the result
only of this general tendency to move toward all sources of weak stimu-
lation. The flatworm proves all things, holding fast only to that which
is good.

In most if not all other invertebrates there occur many “trial move-
ments” similar to those already described. In many recent accounts
of the behavior of other invertebrates little mention, it is true, will be
found of such movements. This is apparently because attention has
been directed by current theories to other features of the behavior, and
the trial movements have been considered of no consequence. Often
an attentive reading of papers on “‘tropisms,”’ etc., will reveal paren-
thetical mention of various “disordered”? movements, turnings to one
side and the other, and other irregularities, which disturb the even tenor
of the ‘“‘tropism,” and are looked upon for some reason as without sig-
nificance and not requiring explanation. Further, one often finds in
such papers accounts of movements which are clearly of the “trial”

- BEHAVIOR IN LOWER METAZOA 247

character, yet are not recognized as such by the author, on the watch
only for “tropisms.” In the earlier literature of animal behavior, be-
fore the prevalence of the recent hard-and-fast theories, one finds the
trial movements fully recognized and described in detail. This is the
case, for example, in the classical papers of Engelmann on behavior in
unicellular organisms, and, as we have seen in detail, for that of Preyer
on the starfish. Moebius, in 1873, gave a lecture on behavior in which
examples of this fact are found. Thus, he describes the reaction of a
large mollusk, Nassa, to chemical stimuli, as shown when a piece of
meat is placed in the aquarium containing them, in the following way:
They do not orient themselves in the lines of diffusion and travel toward
the meat, but move “now to the right, now to the left, like a blind man
who guides himself forward by trial with his stick. In this way they
discover whether they are coming nearer or going farther away from
the point from which the attractive stimulus arises”? (Moebius, 1873,
P- 9).

Unprejudiced observation of most invertebrates will show that they
perform many movements which have no fixed relation to sources of
external stimuli, but which do serve to test the surroundings and thus
to guide the animal. This the present author has observed, for example,
in studies on the leech, on various fresh-water annelids and mollusks,
and in less extended observation on many other animals. As Holmes
(1905) has recently pointed out, in a most excellent paper, this is really
a matter of common observation on all sorts of animals. The fact that
such movements are not emphasized by writers on animal behavior is
evidently due to their being considered without significance.

In a number of recent papers the importance of trial movements in
behavior has been more explicitly recognized. Thus, for the earthworm,
the recent papers of Miss Smith (Mrs. Philip P. Calvert) (1902), of
Holmes (1905), and of Harper (1905) have set this matter in a clear light.
Miss Smith showed that in the reactions of the earthworm Allolobophora
fetida to heat and cold, to chemicals, to drying, and to light, ‘testing
movements” play a large part. When stimulated, the earthworm fre-
quently responds by moving the head first in one direction, then in an-
other, often repeating these movements several times. It then finally
follows up those movements which decrease the stimulation. Holmes
(1905) confirms these results, especially for the reaction of the earth-

_worm to light. His account of the behavior of the earthworm under
the action of light coming from one side may be quoted: “It soon de-
veloped that what seemed at first a forced orientation, the result of a
direct reflex response, is not really such, but that the orientation which
occurs and which is often quite definite is brought about in a more indi-

248 + BEHAVIOR OF THE LOWER ORGANISMS

rect manner by a mode of procedure which is in some respects similar
to the method of trial and error followed by higher forms”’ (/.c., p. 99).
The precise behavior of the earthworm in becoming oriented to light is
described as follows: “‘As the worm crawls it frequently moves the head
from side to side as if feeling its way along. Ifa strong light is held in
front of the worm, it at first responds by a vigorous contraction of the
anterior part of the body; it then swings the head from side to side, or
draws it back and forth several times, and extends again. If in so doing
it encounters a strong stimulus from the light a second time, it draws back
and tries once more. If it turns away from the light and then extends
the head, it may follow this up by the regular movements of locomotion.
As the worm extends the head in crawling it moves it about from side to
side, and if it happens to turn it toward the light it usually withdraws it
and bends in a different direction. If it bends away from the light and
extends, movements of locomotion follow which bring the animal farther
away from the source of stimulus” (/.c., p. 100).

Other observers — Parker and Arkin (1901), Adams (1903) — had
observed that when the earthworm is lighted from one side, it by no means
always turns directly away from that side; Adams, however, showed that
it turns more frequently away from the light than toward it, thus indicat-
ing that the animal has some direct localizing power. This is confirmed
by Harper (1905), who shows that in a strong light the earthworm
Pericheta commonly turns directly away from the source of light,
though if the light is weak, the “‘trial movements” are seen. Harper
gives many other examples of the performance of varied movements
under the action of stimuli in this animal, and brings out some of the
internal factors on which some of these depend.

Holmes (1905) found that the leech and the larva of the blowfly
react to light in essentially the manner which he had found in the earth-
worm. For the leech the following account is given: “In its progress
the leech frequently raises the anterior part of the body and waves it
from side to side as if feeling its way. If the animal turns it in the direc-
tion of a strong light, it is quickly withdrawn and extended again, usu-
ally in another direction. If the light is less strong, it waves its head
back and forth several times and sets it down away from the light; then
the caudal end is brought forward, the anterior end extended and swayed
about and set down still farther away from the light than before. When
the leech becomes negatively oriented, it may crawl away from the light,
like the earthworm, in a nearly straight line. The extension, withdrawal,
and swaying about of the anterior part of the body enable the animal to
locate the direction of least stimulation, and when that is found it begins
its regular movements of locomotion. Of a number of random move-

BEHAVIOR IN LOWER METAZOA 249
ments in all directions only those are followed up which bring the ani-
mal out of the undesirable situation”’ (/.c., p. 102).

In the case of the blowfly larva, Holmes speaks as follows: “ Obser-
vations which I have made upon the phototaxis of blowfly larve with
the problem of orientation especially in mind soon convinced me that
the movements of these forms are directed by light through following up
those random movements which bring them away from the stimulus.
When strong light is thrown on a fly larva from in front, the anterior end
of the creature is drawn back, turned toward one side, and extended
again. Often the head is moved back and forth several times before it
isset down. Then it may set the head down when it is turned away from
the light and pull the body around. If the head in moving to and fro
comes into strong light, it is often retracted and then extended again in
some other direction, or it may be swung back without being withdrawn.
If a strong light is thrown upon a larva from one side, it may swing the
head either toward or away from the light. If the head is swung toward
the light, it may be withdrawn or flexed in the opposite direction, or,
more rarely, moved toward the light still more. If it is turned away from
the light, the larva usually follows up the movement by locomotion.
Frequently the larva deviates considerably from the straight path, but
as it continually throws the anterior part of the body about and most
frequently follows up the movement which brings it away from the stim-
ulus, its general direction of locomotion is away from the light. In
very strong illumination the extension of the anterior part of the body
away from the light is followed by a retraction, since in whatever direc-
tion it may extend it receives a strong stimulus and the larva writhes
about helplessly for.some time. Sooner or later, however, it follows up
the right movement. Occasionally the larva may crawl for some dis-
tance directly toward the light, but after a time its movements carry it
in the opposite direction. When once oriented the direction of locomo-
tion of the larve is comparatively straight ”’ ( /.c., pp. 104-105).

As Holmes points out, these are only examples of a very general
condition of affairs in the lower organisms. We cannot do better, in
concluding this brief section, than to quote some of Holmes’s general
remarks, which show that his observations have led him to essentially
the same conception of behavior that we have reached in the present
work.

“The réle played by the trial and error method in the behavior of
the lower organisms has, as yet, elicited but little comment, owing prob-
ably to the fact that attention has been centred more upon other fea-
tures of their behavior. It may have been considered by some investi-
gators as too obvious for remark, since any one who attentively observes

250 BEHAVIOR OF THE LOWER ORGANISMS

the conduct of almost any of the lower animals for ten minutes can
scarcely fail to see the method exemplified. If he were watching a chick
pecking at a variety of objects and giving signs of disgust when it had
seized a nauseous substance, he would doubtless regard the process as
one of trial and error, whatever name he might apply to it. A study of
the conduct of much lower organisms would disclose many cases almost
equally evident. The lives of most insects, crustaceans, worms, and
hosts of lower invertebrate forms, including even the Protozoa, show an
amount of busy exploration that in many cases far exceeds that made
by any higher animal. Throughout the animal kingdom there is obedi-
ence to the Pauline injunction, ‘ Prove all things, hold fast to that which
is good’”’ (/.c., p. 108).

The well-known behavior of hermit crabs in finding suitable shells
in which to live and in changing shells which have become unsuitable
shows a systematic application of the method of trial extending to the
details of the behavior. This is well brought out in the excellent analysis
of this behavior given by Bohn (1903).

Behavior of higher animals based on the selection of the results of
varied movements —the ‘method of trial and error” — plays, as is
well known, a large part in recent discussions of that subject. The
- work of Thorndike (1898) on behavior in the cat, and the books of
Lloyd Morgan (1900), in which this matter is dealt with, are, of course,
well known, and require no discussion on our part. The fact that be-
havior of this character plays a large part in higher, as well as in lower,
organisms, is of the greatest interest, as showing that this method is
one of fundamental and general importance. But with the details in
higher animals we are not here concerned.

3. MOopIFIABILITY OF BEHAVIOR AND ITS DEPENDENCE ON PHysIo-
LOGICAL STATES

In the section preceding the present one we have described many
cases of behavior in the lower invertebrates in which the animal, under
the action of constant external conditions, passes from one form of be-
havior to another. All such cases are illustrations of the fact that be-
havior depends upon internal, physiological conditions, as well as upon
external stimuli. Since under the same external conditions the action
changes, the animal must itself have changed, otherwise it could not now
behave differently from before. It is clear that the continuance of a
stimulus, or the performance of a certain action, may change the physio-
logical state of the animal so as to induce new reactions.

In some cases the varied actions performed under stimulation have

BEHAVIOR IN LOWER METAZOA_ | ; 251

been spoken of as random movements (Holmes, 1905). The word
“‘random,” of course, implies only that these movements are not defined
by the position of the stimulus; it does not signify that the move-
ments are undetermined. The principle of cause and effect applies to
these movements as well as to others. But the causes lie partly within
the animal; each phase of the movement aids in determining the suc-
ceeding phase. The earthworm may turn to the right at a given instant
merely because it has just before turned to the left. Reactions in which
a succeeding phase is determined by a previous one have sometimes been
called chain reflexes (Loeb, 1900; Driesch, 1903). If this term is used,
it needs to be kept in mind that in most cases the succeeding phase is not
invariably and irrevocably called up by the preceding one, as is implied
by this term. On the contrary, the relation between the two is extremely
variable. One type of action may be repeated many times before the
second type comes into play, and the order of the different actions is by
no means always the same. ‘Thus the preceding phase is only one factor
in deciding what shall be the present action. The latter depends upon
the entire physiological state of the organism, which is determined by
various factors. Illustrations of this are seen in the righting reaction of
the starfish and many other animals; in the series of reactions by which
Stentor responds to a mass of carmine grains in the water (p. 174); in
that by which Stoichactis gets rid of waste matter lying on the disk (p. 202),
and the like.

The diverse physiological states of lower organisms have been little
studied. This is partly because it is rarely possible to observe them di-
rectly; it is only through their effects upon action that they become
evident. Thus the real data of observation are the actions; if we con-
sidered these alone, we could only state that a given organism reacts under
the same external conditions sometimes in one way, sometimes in another.
This would give us nothing definite on which to base a formulation and
analysis of behavior, so that we are compelled to assume the existence
of changing internal states. This assumption, besides being logically
necessary, is, of course, supported by much positive evidence drawn from
diverse fields, and there is reason to believe that in time we shall be able
to study these states directly. Before we can come to a full understand-
ing of behavior, we shall have to subject the physiological states of
organisms to a detailed study and analysis, as to their objective nature,
causes, and effects.

The most noticeable and therefore best-known physiological states
of lower animals are those which depend upon changes in metabolism.
The reactions of the starfish and the planarian to many chemical and
mechanical stimuli depend, like those of the sea anemone, on the

252 BEHAVIOR OF THE LOWER ORGANISMS

progress of metabolism. Hungry animals react positively to possible
food, while satiated ones react negatively to the same stimuli. This
most significant relation is, of course, almost universal in organisms;
it shows directly the dependence of behavior on the relation of external
agents to internal processes.

V. Uexkiill has made precise studies of certain physiological states
and of the factors on which they depend, in the sea urchin and a number
of other lower animals. In the sea urchin, some of the pedicellarie
will not close in response to a mechanical stimulus, save in case this has
been preceded by a chemical stimulus. The latter changes the physio-
logical state of the protoplasm (muscle or nerve), so that it now reacts
to a stimulus which before would have had no effect. The spines of the
sea urchin usually bend toward a spot on the surface of the body that is
mechanically stimulated, as by a needle. _ But if this stimulus has been
preceded by the action of a chemical, the spines now reverse the reaction
and bend away from the region stimulated, Many such changes in
physiological state are brought by v. Uexkiill under the heading of
changes in /onus of the muscles or nerves. Steady tension, such as is
produced in certain muscles by pressing a spine of the sea urchin to one
side, decreases the tonus, so that the muscles are no longer so tense as
before. Such muscles react more readily to stimuli than do those of
higher tonus. Sudden jarring produces the opposite effect, the muscles
pull harder and react less readily than before. Decrease of tonus caused
by tension is transmitted in some way to neighboring spines, so that
after a certain spine has been pressed to one side, all those about it bend
in the same direction and react more readily than before. These changes
in physiological state play a large part in determining the behavior of
the sea urchin under natural conditions.

Besides such changes, there are in the sea urchin others that are less
easy to formulate, and that have not been analyzed. V. Uexkiill found
that the set reflexes of the spines and the changes in tonus mentioned
above impose on the sea urchin a behavior that under most conditions
seems stereotyped and predictable. This leads the author named to
contrast the sea urchin as a “republic of reflexes’”’ with higher animals
in which the behavior is unified. But the difference is only one of de-
gree. Ifthe sea urchin is placed on its back, the usual reflexes and their
stereotyped interrelations would not restore the animal to the natural
position, but merely cause it to walk forward while lying on its back.
As a result, we find a physiological state induced that causes a thorough-
going change in the behavior of the spines. They now move in such a
way as to turn the sea urchin again on its ventral surface. As v. Uex-
kiill says, the behavior of the spines is variable and capable of adapta-

BEHAVIOR IN LOWER METAZOA 253
tion (“‘variabel und anpassungsfahig,” 1900, p. 98). This adaptation,
under unusual conditions, of the movements of the spines to the needs of
the organism as a whole, seems to remove all difference in principle
between the behavior of the sea urchin and that of higher animals.

Many illustrations of varied physiological states could be given from
an analysis of the behavior of the starfish in the righting reaction, and
in the various experiments devised by Preyer (see p. 239). _

In the flatworm Planaria the work of Pearl (1903) shows that the be-
havior depends largely upon the physiological state. In this animal the
following different states determining behavior may be distinguished :—

1. Conditions of hunger and satiety, determining the reactions to
food in a regulatory way.

2. A resting or “sleeping” condition. The animal is often found
lying quietly under rocks, the muscles relaxed. In this condition it
fails to react to weak stimuli, but strong stimulation induces the negative
reaction, followed by continued activity.

3. The condition of normal, undisturbed activity. The animal now
responds to weak stimuli of all sorts by the positive reaction, turning
toward the side stimulated, while strong stimuli cause the negative
reaction.

4. A condition of heightened activity, in which the worm makes
many “‘testing’’ movements with the head, and reacts positively to most
stimuli, whether strong or weak. In this condition the planarian makes
the appearance of actively seeking something, and of following up any
source of stimulation which it finds.

5. An “excited” condition, produced by stimulating the animal
strongly and repeatedly. In this condition the animal moves about vio-
lently and reacts negatively to most stimuli to which it reacts at all.

6. Possibly due to an accentuation of the condition last described is
a change of reaction observed by Pearl when one side of the head of an
excited specimen is stimulated by repeated blows. At first the animal
turns farther and farther away from the side stimulated. Then suddenly
it jerks strongly backward, and turns far in a direction opposite its
previous turning — that is, toward the side stimulated. ‘The reaction
appears as if, after the animal had tried in vain to get away from an un-
comfortable stimulus by its ordinary reaction, it finally tries a wild jump
in the opposite direction”? (Pearl, 1903, p. 580).

The different physiological conditions are determined largely by the
history of the individual worm, so that in this sense its behavior may be
said to depend on its experience. The dependence of the reactions on
the physiological state is in a given specimen very great, so that two in-
dividuals often react in opposite ways to the same stimulus. The same

254 BEHAVIOR OF THE LOWER ORGANISMS

individual that reacts to a given stimulus positively may a little later
react negatively, and vice versa. After long study of Planaria, Pearl
concludes that “‘it is almost an absolute necessity that a person should
become familiar, or perhaps better, intimate, with an organism, so that
he knows it in something the same way that he knows a person, before
he can hope to get even an approximation of the truth regarding its
behavior.” This remark might be extended to most lower animals.

As we have seen in a previous section (p. 236), the behavior of the
flatworm shows certain well-defined reaction types, which might, taken
separately, be called reflexes. But when we consider the various factors
which determine the production and combination of these reaction types,
we cannot consider the behavior of the flatworm as “purely reflex,”
if we mean by reflexes invariable reactions to the same external stimuli.
On the contrary, the behavior is extremely variable in accordance with
many conditions, internal as well as external.

A detailed analysis of the behavior of almost any of the lower inver-
tebrates would show as many different physiological conditions on which
behavior depends as we find in the flatworm. In the earthworm, for
example, the conditions are still more complicated than in the flatworm,
so that the same external stimulus, acting with the same intensity, and
applied to the same spot on the body, may produce any one of at least
six different reactions. The variations of internal state as the animal
moves about are what condition the “random movements’’ described
by Holmes in the reactions to light, and by Smith in the reactions to other
stimuli (see p. 247).

Of special interest are changes in state that lead to more or less per-
manent modifications in behavior. These are little known in the lower
organisms. Most of the changes of physiological state described in the
foregoing paragraphs are not known to last more than a short time.
In Vorticella, Hodge and Aikins (1895) state that the modified behavior
endured for five hours; this perhaps needs confirmation. In the lowest
organisms it is difficult to carry out experiments that shall determine
how long modifications last. Perhaps the lowest animal in which an
enduring modification of behavior has been demonstrated is the flatworm
Convoluta roscoffensis. This is one of the lowest of the group, belong-
ing to the division Accela, which includes the simple forms having no
alimentary canal. The behavior of Convoluta, as described by Gamble
and Keeble (1903), and by Bohn (1903 a), presents many features of
the greatest interest; into only a few of these can we enter. Convoluta
is a small green worm that lives in immense numbers on the sand of the
seacoast of Brittany, just above the water line. It forms thus large
green patches. When the tide rises the water covers the region where

BEHAVIOR IN LOWER METAZOA 255

Convoluta is found, and the waves would wash the animals away, if
their behavior did not prevent. As the water rises and the waves begin
to beat on the sand near them, they go downward into the sand, where
they are protected. As the water sinks, the animals creep upward and
appear again at the surface. These upward and downward movements
are reactions with reference to gravity, as is shown by placing the animals
on smooth, inclined, or perpendicular surfaces. They go downward
as the tide rises, upward as it falls. Bohn (1905) has shown that many
littoral mollusks and annelids show similar movements with relation to
the tides.

The peculiarly interesting fact concerning this behavior in Convoluta
is the following: This periodical alternation of reactions, produced by
an environmental factor, becomes so. impressed on the organization of
the animal that it occurs even when this factor is lacking. The alterna-
tion of movement has become habitual. If the worms are removed
to an aquarium where the tide no longer acts upon them, they continue
to go downward at the period of high tide, upward at the period of low
tide. This continues for about two weeks, so that the worms may be
carried far away from the shore, and may then be used for a time as tide
indicators. But under such conditions the periodicity after a time dis-
appears, showing that it was really due to the external factor, — the tides.
This appears to be the lowest known case of what we call in higher
animals a habit.

In some of the higher invertebrates, lasting modifications of behavior
of a still more complex character may be induced experimentally. This
has been accomplished in the Crustacea by Yerkes (1902), Yerkes and
Huggins (1903), and Spaulding (1904).

With the crayfish and crab, Yerkes and Huggins (1903) studied
the modification of behavior in escaping from danger and in finding
water. The crayfish was placed in one
end of an inclined pen which opened at
the other end into the water. The pen
was partly divided by partitions in such a
way as to leave two passages leading to
the water (Fig. 139). Either of these pas-
sages could be closed at its end by a glass
plate G. The animal was placed at T ,, pas eS Bown Re
(Fig. 139). In moving away from this After Yerkes. See text.
region it might.enter the blind pocket at G, thus not directly reaching the
water, or it might go through the other passage straight to the water.

After some preliminary experiments without closing either passage,
showing that the animals were as likely to pass to the right as to the left,

256 BEHAVIOR OF THE LOWER ORGANISMS

the partition was placed in the right passageway, as in Fig. 139. The
crayfish which turned to the left on leaving T escaped at once to the water.
But if it turned to the right it passed into the pocket G, and was compelled
to explore the region, finally turning to the left and passing the partition
P, before it could escape. Three individuals were given sixty trials each
in the course of thirty days. In the first ten trials they went just as fre-
quently into the blind passage as toward the water. In the second ten
trials, the animals started in 60 per cent of the cases toward the open
passage at the left. In the next ten trials this proportion had risen to
75.8 per cent; in the following ten, to 83.3 per cent. In the last ten
trials of the sixty, very few mistakes were made. In go per cent of all ©
cases they went straight for the open passage. In another series of
experiments an individual, after four hundred trials, made only one
mistake in fifty trials. Similar results were obtained by Yerkes (1902)
in experimenting on the crab Carcinus granulatus.

Thus at the beginning of the experiment the animals were as likely
to go to the right as to the left, while at the end they went almost inva-
riably to the left. Since the external conditions had not changed, the
animals themselves must have changed. Their internal condition now
differed in some way from the original condition.

Yerkes and Huggins (1903) endeavored to determine how easily
this acquired condition could be modified or destroyed. After the cray-
fish had learned to go through the open passageway so as to make a mis-
take in only one case in ten, the experiments were discontinued for two
weeks. On the fourteenth day the animals were still inclined to go
- straight to the open passage, though the habit had become dulled, and
they now made mistakes in about three cases out of ten.

In other experiments, after the animals had acquired the habit of
escaping through the right passage, the partition G was changed, so as to
block up this passage, but
leave the left one open.
—, L At the next trial the ani-
"y sS mal made a long-continued

attempt to escape by the
right-hand passageway, fol-

lowing the path shown in

Fic. 140.—Path followed by a crayfish which has
formed the habit of escaping to the water by the right- Fig. —_ It wandered
hand passageway, when this passage is closed and the about for fifteen minutes

left one opened. After Yerkes and Huggins. before discovering the open
way. But in the next trial it turned to the left, and thereafter it
turned almost as regularly to the left as it had before turned to the
right.

BEHAVIOR IN LOWER METAZOA 257

This habit formation took place in the same er when the floor
of the pen was carefully washed out after each ie showing that the
animals were not merely following a path marked by an odor from the
previous passage along it. It was evident that the customary direction
of turning played a large part in the behavior. When the left passage
was closed, the crayfish that had erred into this passage escaped by turn-
ing to the right, as indicated by its path in Fig. 141. When after the
establishment of this habit, the right passage was closed (Fig. 140),
the animal tried persistently to escape from this passage by turning to
the right, as it had previously done.

Spaulding (1904) studied the modifiability of behavior in the food
reactions of the hermit crab. These animals tend to remain in the lighted
parts of the aquarium. They were fed by placing a small, dark screen
with a fish beneath it in a certain part of the aquarium. The diffusion
of juices from the fish set the
crabs to moving about ac- L
tively, and in the course of .
time some passed beneath oa
the screen. Here the food R
was found. At first it took
the crabs a long time to find

it under these conditions. é Fic. 141. — Path followed by crayfish while being
tlie rst day only, three ase! sed ts Ff. peeps, Os Seale
out of thirty succeeded in the habit of turning to the right. After Yerkes and
fifteen minutes. But by the “Uses

third day, twenty of the thirty had passed beneath the screen fifteen
minutes after it was introduced. At the end of the eighth day, twenty-
eight out of the twenty-nine present had passed beneath the screen
inside of five minutes. The crabs had become so modified that they
went quickly beneath the screen as soon as it was introduced.

Now the experiments were varied by placing in the aquarium the
screen alone, without the food. Most of the animals passed beneath
it as before. Thus, on the thirteenth day of the experiments, twenty-
five specimens out of twenty-seven present had passed under the screen
within five minutes. After they had entered they were fed, in order that
the association between the screen and food might not be destroyed.

Phenomena of this character are usually spoken of as learning, or
as the formation of habits or associations. The facts may be expressed
in a purely objective way as follows: When subjected to the stimulus
of the screen and the food, the animals reacted to the food by gathering
about it — incidentally of course gathering under the screen. After
many repetitions of such stimulation, the animals had become changed

s

258 BEHAVIOR OF THE LOWER ORGANISMS

so that they respo to the dark screen alone by the reaction proper
to food. We shall analyze these phenomena more fully in our general
discussion of behavior (Chapter XVI).

These processes, by which behavior becomes more or less enduringly
modified, are known to play a large part in the behavior of higher inver-
tebrates, such as ants and bees, and in the vertebrates. As investigation
progresses, we find analogous processes lower and lower in the animal
scale. It was only eight years ago that Bethe (1898) could deny their
occurrence even in ants and bees; now they have been fully demonstrated
in these and much lower animals. The study of these matters has hardly
begun, and it is not too much to say that no experiments have been
carried through on the lowest invertebrates that would show this lasting
modifiability, even if it exists. We are therefore still in the dark as to
how far downward such modifiability extends; time may show it to be
a universal property of living things.

The importance of this modifiability for the understanding of behavior
is obviously great. Where such modifiability exists, the definite “reflex”
is not to be considered a permanent, final element of behavior. On the
contrary, it is something developed, and it must differ in individuals
with different histories. Two specimens of Convoluta side by side might
show at the same moment, one “ positive geotropism,” the other “ nega-
tive geotropism,” depending on their past history. Whether a hermit
crab will pass beneath a dark screen, or will avoid it, is not determined
by the permanent properties of its colloidal substance; this can be pre-
dicted only by knowing the history of the individual.

The process by which an organism acquires a definite reaction which
it before had not is, of course, nothing mystical, but an actual physio-
logical one, whose progress is open to investigation as is that of any other.
It needs to be studied and analyzed in the same objective way as the
circulation of the blood. The power of changing when acted upon by
outer agents, in such a way as to react differently thereafter, is one of the
most important properties of living matter, and it is misleading to ignore
this property and deal with animals as if their reactions were invariable.
How the modifications occur is one of the fundamental problems of
physiology. We must remember that even what we call memory, in-
telligence, and reasoning are composed objectively of certain physio-
logical processes. In other words, as Liebmann has emphasized, ‘there
are objective material processes that follow the laws of intelligence, of
reasoning, of logic. This is a capital fact. In searching for the laws of
life processes we must remember that those just mentioned are as real as
any others, and their laws must be provided for in the physics and
chemistry of colloids if these are to give us the laws of life processes.

BEHAVIOR IN LOWER METAZOA 259

We shall attempt to analyze some of these matters farther in our general
discussion of behavior, which forms the remainder of the work.

LITERATURE XII

A. Behavior of echinoderms: UEXKULL, 1897, 1897 a, 1899, 1900, I900 a;
PREYER, 1886; ROMANES, 1885.

B. Behavior of planarians: PEARL, 1903; MAST, 1903.

C. Behavior of Rotifera: JENNINGS, 1904 d.

D. Reaction by varied movements in other invertebrates : SMITH,-I902 ; HOLMEs,
1905; BOHN, 1903; MOEBIUS, 1873; HARPER, I905.

~ £&. Method of trial and error in vertebrates : THORNDIKE, 1898 ; MORGAN, Igoo.

F. Modifiability of behavior in lower animals: BOHN, 1903 a, 1905; GAMBLE
AND KEEBLE, 1903; JENNINGS, 1904 @; YERKES, 1902; YERKES AND HUGGINS,
1903; SPAULDING, 1904.

PART ITT

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS,
WITH A DISCUSSION OF THEORIES

CHAPTER XIII

COMPARISON OF BEHAVIOR OF UNICELLULAR AND MULTI-
CELLULAR ORGANISMS

We have now examined the behavior of a number of Protozoa and
of a number of Metazoa. What characteristic differences do we find
between the two?

This question is of interest from a number of points of view. The
Protozoa consist each of but a single cell, while the Metazoa are com-
posed of many cells, which are differentiated for the performance of
different functions. Does this difference in structure correspond to any
fundamental difference in behavior? Le Dantec (1895) proposed to
distinguish the life manifestations of the Protozoa as “ elemental life ”
from the life of the Metazoa, holding that the two are so different in
fundamental character that it is improper to apply the same name to
them; this point of view is often met in scientific literature. The life
of the Protozoa is considered “as the direct result of the diverse reactions
of a small mass of a certain chemical substance in the presence of appro-
priate substances ”’ (/.c., p. 26), while that of the Metazoa is “ the result
of the functioning of an extremely complicated machine, in which the
reactions of the chemical in question serve as motor power.” The
former is compared to the burning of the alcohol in an alcohol motor,
the latter to the functioning of the motor itself (p. 27). We are inter-
ested in the question whether this theoretically fundamental difference
shows itself in any way in the phenomena to be observed. Is there any
objective evidence in the behavior for the belief that the life of the Pro-
tozoa differs fundamentally from that of the Metazoa?

Again, the Metazoa possess a nervous system, while the Protozoa
have none. To the specific properties of the nervous system many of
the manifestations of behavior in higher animals have been attributed.
This system is often considered an essential prerequisite for certain

260

COMPARISON OF PROTOZOA AND METAZOA 261

fundamental features of behavior. Do we find a striking difference in
the behavior of organisms after a nervous system has been developed?
What can animals do without a nervous system? A comparison of
organisms with and those without this system should give us evidence as
to the real nature of the functions of the latter, and will perhaps
prevent us from overestimating its importance.

We will sum up briefly in a number of paragraphs the resemblances
and differences between the behavior of animals with and without a
nervous system.

1. First, we find that in organisms consisting of but a single cell,
and having no nervous system, the behavior is regulated by all the dif-

ferent classes of conditions which regulate the behavior of higher animals.

In other words, unicellular organisms react to all classes of stimuli to
which higher animals react.’ All classes of stimuli which may affect

the nervous system or sense organs may likewise affect protoplasm
without these organs. Even the naked protoplasm of Amceba responds
to all classes of stimuli to which any animal responds. The nervous
system and sense organs are therefore not necessary for the reception of
any particular classes of stimulations.

2. The reactions produced in unicellular organisms by stimuli are

| not the direct physical or chemical effects of the agents acting upon them,
but are indirect reactions, produced through the release of certain forces

already present in the organism. In this respect the reactions are com-
parable with those of higher animals. This is true for Amceba as well
as for more differentiated Protozoa.

3. In the Protozoa, as in the Metazoa, the structure of the organism
plays a large part in determining the nature of the behavior. There are
only certain acts which the organism can perform, and these are condi-
tioned by its organization; by one of these acts it must respond to any
stimulus. If the behavior of the Metazoa is comparable in this respect
to the action of a machine, the same comparison can be made for the
behavior of the Protozoa.

4. Spontaneous action — that is, activity and changes in activity
induced without .external stimulation — takes place in the Protozoa
as well as in the Metazoa. Both Vorticella and Hydra, as we have seen,
spontaneously contract at rather regular intervals, even when the external
conditions remain uniform. Continued activity is the normal state of
affairs in Paramecium and most other infusoria. The idea that spon-
taneous activity is found only in higher animals is a totally erroneous
one; action is as spontaneous in the Protozoa as in man.

1 Considering auditory stimulation as merely a special case of mechanical stimulation.

262 BEHAVIOR OF THE LOWER ORGANISMS

| §- In unicellular organisms, without a nervous system, certain parts
of the body may be more sensitive than the remainder, forming thus a
region comparable to a sense organ in a higher animal. Whether such

a part may become more sensitive to one form of stimulation, while ~

insensitive to others, as in higher organisms, seems not to have been
determined.

6. Conduction occurs in organisms without a nervous system. This
is, of course, seen in the fact that a stimulus limited to one part of the
body may cause a contraction of the entire body, or a reversal of cilia
over the entire body surface. A strongly marked case is the contraction
of the stalk in Vorticella, when only the margin of the bell is stimulated.

7. Summation of stimuli occurs in Protozoa as in Metazoa. This

is shown most clearly in Statkewitsch’s experiments with induction
shocks (p. 83). Weak induction shocks have no effect until frequently
repeated.

8. In the unicellular animal, as in that composed of many cells, the
reaction may change or become reversed as the intensity of the stimulus

Rgres though: the quality of the stimulus remains the same. Such
a change in reaction has sometimes been claimed as a specific property
of the nervous system. The protozoans Amoeba and. Stentor, as well
as the metazoan Planaria, move toward sources of weak mechanical
stimulation, away from sources of strong stimulation.

g. In the Protozoa, as in the Metazoa, the reaction may change while

: the stimulus remains the same. That is, the animal may respond at
first by a certain reaction; later, while the stimulus remains the same,
by other reactions. This has been shown in detail in the account of
Stentor (Chapter X). The change may consist in either a cessation of
the reaction, or in a complete alteration of its character. These changes
are, as a rule, by no means due to fatigue, but are regulatory in character.
The behavior thus depends on the past history of the organism. For
-such modifications of behavior a nervous system is then unnecessary.

10. In the Protozoa, as in the Metazoa, the reactions are not invari-

\ able reflexes, depending only on the external stimulus and the anatomi-

cal structure of the organism. The reaction to a given stimulus de- ©

pends upon the physiological condition of the organism. In Stentor
we could distinguish at least five different conditions, each with its char-
acteristic reaction to the given stimulus.

11. In unicellular as well as multicellular animals we find two chief |

general classes of reactions, which may be designated positive and nega-
tive. The positive reaction tends to retain the organism in contact

with the stimulus, the negative to remove it from the stimulus. In many

classes of stimuli we can distinguish an optimum condition. A change

COMPARISON OF PROTOZOA AND METAZOA 263

leading from the optimum produces a negative reaction, while a change
leading toward the optimum produces no reaction, or a positive one.
The optimum from this standpoint usually corresponds, in a broad
way, to the optimum for the general interests of the organism. These
relations hold equally for Protozoa and Metazoa.

12. In both the Protozoa and the Metazoa that we have studied, the
behavior is based to a considerable degree on the selection of certain
conditions through the production under stimulation of varied move-
ments (see Chapter XII). This shows itself in two characteristic types.
In the one case the organism when subjected to a change leading away
from the optimum responds by a movement that subjects it successively
to many different conditions, finally remaining in that one which is
nearest the optimum. This form of reaction is strongly developed in
Paramecium. In the second type, which may be considered a devel-
opment of the first, the organism first responds by one reaction, then
by another, continuing at intervals to change its response until one of
the reactions frees it from the stimulation. This way of behaving is
well seen in Stentor. Both methods of reaction may be expressed as
follows: When the organism is subjected to an irritating condition, it
tries many different conditions or many different ways of ridding itself
of this condition, till one is found which is successful.

All together, there is no evidence of the existence of differences of fun-
damental character between the behavior of the Protozoa and that of
the lower Metazoa. The study of behavior lends no support to the
view that the life activities are of an essentially different character in the
Protozoa and the Metazoa. The behavior of the Protozoa appears to
be no more and no less machinelike than that of the Metazoa; similar
principles govern both.

’ Further, the possession of a nervous system brings with it no observ-
‘able essential changes in the nature of behavior. We have found no
important additional features in the behavior when the nervous system
‘is added. In the lower Metazoa, experiment has shown the nervous
system to have two chief functions, — the maintenance of tonus, and the
bringing of the parts of the body into relation with each other by serving
for conduction. But both these functions are performed in the Protozoa
without a nervous system. The body of Paramecium maintains marked
tonus, and the different parts of the body work together. A comparison
of the behavior of the Protozoa with that of the lower Metazoa lends
powerful support to that view of the functions of the nervous system
which is so ably maintained by Loeb in his brilliant work on “The Com-
parative Physiology of the Brain and Comparative Psychology.” Accord-
ing to this view we do not find in the nervous system specific qualities

264 BEHAVIOR OF THE LOWER ORGANISMS

not found elsewhere in protoplasmic structures. The qualities of the
nervous system are the general qualities of protoplasm. Certain of
these general qualities have become much accentuated in the protoplasm
of the nervous system, while in the remainder of the protoplasm of the
metazoan body they are less strongly marked, being partially obscured
by differentiations in other directions. Most if not all of the funda-
mental activities which have been considered peculiar to the nervous
system may be demonstrated, as we have seen, in the Protozoa, yet in
them no nervous system exists.

These facts show the necessity of guarding. against overrating the
importance of the nervous-system. It is doubtful if the nervous system
is to be considered the exclusive seat_of anything; its properties are
accentuations of the general properties of protoplasm. Dogmatic state-
ments as to the part necessarily played by the nervous system in given
cases must be looked upon with suspicion unless supported by positive
experimental results. If acts objectively identical with “reflex actions”
and still more complex types of behavior may exist in the Protozoa with-
out the intervention of a nervous system, it is not impossible that they
"may occur in the same manner in Metazoa, as Loeb has maintained.
Where a nervous system exists, we are not justified in dogmatically refer-
ring all phenomena of behavior to it, for other protoplasm exists too, and
may still retain some of the characteristics which it had in the Protozoa.
In an animal possessing a nervous system we cannot tell without experi-
mentation whether a given reflex action or other reaction depends on
the nervous system or not. The possibility always remains open that
the remainder of the protoplasm may perform the act in question by its
own capabilities, as it does in the Protozoa. In any animal, we are
justified in attributing exclusively to the nervous system only those prop-
erties which rigid analytical experimentation shows it alone to possess.

CHAPTER XIV

TROPISMS AND THE LOCAL ACTION THEORY OF TROPISMS

A LARGE share of the behavior of lower as well as of higher animals
consists of movements either toward or away from certain objects or
sources of stimulation. Behavior can thus be largely classified into
two great classes: “positive and negative” reactions; movements of
“attraction and repulsion,” of approach and retreat. To account
in a general way for these directed movements certain theories have
_ been proposed, and one of these has become widely accepted. This is
_ the so-called “tropism theory.” The word “tropism” has been used in
_ several different senses by different authors, and not always as imply-

ing a definite theory (see page 274). But there is a certain theory

which is usually implied when tropisms are mentioned; it has* become

so generally accepted that it is often spoken of as the tropism theory.
_ It will perhaps be more accurate to speak of it as the local action theory
of tropisms. ‘‘Tropisms” has become the key-word for the behavior
of lower organisms, and the theory mentioned is supposed to furnish
explanation of most of the puzzles found in this field. A theory so
generally accepted demands separate special treatment. What is this
tropism theory as usually understood in discussions of animal behavior,
and how far does it go in helping us to understand the behavior of lower
organisms ?

According to this tropism theory the primary feature in the directed’
"ese of lower organisms is the position or orientation of the body %
with respect to the source of stimulation, and this orientation is brought
about by the direct local action of the stimulating agent on that part of
the body on which it impinges. The essential points in this theory are
then two: first, orientation; second, the production of orientation by

local action. These points we may consider separately.
(1) By this tropism theory a stimulus is considered to force the

nimal to take a certain position with respect to the direction from which ~
he stimulus comes; in this position it is said to be oriented. Usually
the organism becomes oriented with anterior end either toward or away
from the source of stimulation. This is the essential feature in the action
of the stimulus. ‘‘The essential point in all directive stimulation is
265

266 BEHAVIOR OF THE LOWER ORGANISMS

x therefore the axial orientation of the cell body, and the central point in
the mechanism of this phenomenon, lies in the explanation of this axial
position” (Verworn, ‘General Physiology,” 1899, p. 480). After the
animal has thus become oriented it may move forward in the usual
way. If it does so, it will of course incidentally move toward or away
from the source of stimulation, but this approach or retreat is not an
essential or determining part of the reaction. ‘The really fundamental
phenomenon which characterizes these directed movements is always
not so much the forward movement as such, as rather a process which
may be called a movement of orientation. The organism places its
axis in a definite localized relation to the stimulus, which may be photic,
thermic, chemical, etc. That is, it places its axis either in the direction
of the stimulation or perpendicular to it (diatropism). In the former
case the ‘anterior’ end may be directed ‘positively,’ toward the source of
stimulation, or ‘negatively,’ away from it. It now appears a matter of
course that if forward motion takes place after such orientation, its
direction wil correspond to the direction of the stimulus” (Driesch,
1903, p. 5, translation).

(2) This orientation is produced, according to this tropism theory,
by the direct action of the stimulating agent on the motor organs of that
side of the body on which it impinges. A stimulus striking one side of
the body causes the motor organs of that side to contract or extend or
to move more or less strongly. This, of course, turns the body, till the
stimulus affects both sides equally; then there is no occasion for further
turning, and the animal is oriented. ‘These tropisms are identical
for animals and plants. The explanation of them depends first on the
specific irritability of certain elements of the body surface, and, second,
upon the relations of symmetry of the body. Symmetrical elements at
the surface of the body have the same irritability; unsymmetrical ele-

ments have a different irritability. Those nearer the oral pole possess —

an irritability greater than that of those near the aboral pole. These
circumstances force an animal to orient itself toward a source of stimu-
lation in such a way that symmetrical points on the surface of the body
are stimulated equally. In this way the animals are led without will of
their own either toward the source of stimulus or away from it’’ (Loeb,
1900, p. 7). Holt and Lee (1901, pp. 479-480) bring out this point in
the prevailing theory, as applied to light, as follows: ‘The light operates,
naturally, on the part of the animal which it reaches. The intensity of
the light determines the sense of the response whether contractile or
expansive, and the place of the response, the part of the body stimulated,
determines the ultimate orientation of the animal.”

How the orientation is brought about according to this theory may

THE TROPISM THEORY 267

be illustrated most simply by considering an organism covered with
cilia. For this purpose we may employ the accompanying diagrams,
based on those given by Verworn (1895, p. 484), but modified to make
them clearer. In Fig. 142 a stimulus is supposed to act from the right

|

ek |
\

Fic. 143. — Diagram of a positive reaction, according to the local action theory of tropisms.

Fic. 142. — Diagram of a negative reaction, according to the local action theory of tropisms.

side on the organism, as indicated by the arrows, and to cause the cilia
of that side to contract more strongly, as is indicated by the heavier
shade and greater curving. This must, of course, turn the body to the

left, as a boat is turned to the left when the right oar is more strongly

268 BEHAVIOR OF THE LOWER ORGANISMS

pulled. The animal therefore occupies successively the positions 1, 2, 3,
and 4. In the position 4 both sides are équally affected by the stimulus,
so that there is no cause for further turning. The animal has become
oriented and its usual forward movements now take it away from the
source of stimulation. We have here a case of negative tropism or
taxis.

Figure 143 illustrates the conditions producing positive tropism or
taxis. The stimulus, coming from the right side, is supposed to cause
the cilia of that side to beat less strongly backward, or to beat forward.
As a result the organism is turned to the right, through the positions
I, 2, 3, 4, till its anterior end is directed toward the source of stimulation.
Both sides are now affected alike, and there is no cause for further turn-
ing. The animal now moving forward in the usual way of course travels
toward the source of stimulation.

As an example of the application of the sania scheme to a mus-
cular organism, we may take Davenport’s exposition of the action of
light in determining the direction of locomotion of the earthworm.
“Represent the worm by an arrow whose head indicates the head en]
(Fig. 144,A). Let solar rays SS fall upon it horizontally and perpendicu-
larly to its axis. Then the impinging ray strikes it laterally, or, in other
words, it is illuminated on one side and not on the other. Since, now,
the protoplasm of both sides is attuned to an equal intensity of light,

that which is the less

Ss S illuminated is nearer its
optimum intensity. Its
protoplasm is in a photo-
re tonic condition. That
Ri Low light attunement which is strongly illumin-

Fic. 144. — Diagram to explain a tropism in a muscu- ated has lost its phototonic
lar organism, such as the earthworm. After Davenport. condition. Only the dark-
Se fat ened muscles, then, are
capable of normal contraction; the brightly illuminated ones are re-
laxed. Under these conditions the organism curves toward the darker
side; and since its head region is the most sensitive, response begins
there. Owing to a continuance of the causes, the organism will con-
tinue to turn from the light until both sides are equally illuminated,
z.e. until it is in the light ray. Subsequent locomotion will carry the
organism in a straight line, since the muscles of the two sides now act
similarly. Thus orientation of the organism is effected. The same
explanation, which is modified from one of Loeb (’93, p. 86), will ac-
count, mutatis mutandis, for positive phototaxis” (Davenport, 1897,
Pp. 209).

Low light attunement

THE TROPISM THEORY 269

From thé relations above set forth, it follows that for determinatio
of the direction of movement in accordance with this tropism theory,
a stimulus must act upon one portion of the body differently f
more intensely than on other parts.. Without such differential
on different parts of the body there is nothing to cause the a
turn in one direction or another.

This tropism schema is made by its upholders the
larger part of the directed activities of the lower anima
phenomena of positive and negative chemotaxis, ther
taxis, and galvanotaxis, which are so highly interesting
in all organic life, follow with mechanical necessity asthps
of differences in biotonus, which are produced by the action ofSt
at two different poles of the free-living cell” (Verworn, 1899, p. 503).
Verworn (1899) and Loeb (1900) have developed the theory as a general
explanation for all sorts of directed activities, and many authors have
accepted it for reactions to particular stimuli. In recent times, Holt
and Lee (1901) have applied it in detail to the responses to light, Loeb
(1900, p. 186) and Garrey (1900) to chemicals, Loeb (1897) and Verwork
(1899) to gravitation, Mendelssohn (1902 a) to heat and cold.

In the foregoing chapters we have examined the behavior of a con-
siderable number of lower organisms, of many different kinds. How
far does this examination support the above theory? How far is the
observed behavior due to orientation produced by the local action of

stimuli on the different parts of the body? To what extent does this
- ‘tropism theory aid us in understanding the behavior of these organisms ?

In Ameeba there are no permanent body axes; anterior and posterior
ends continually interchange places in the rolling movement, and any
part may become at any time the advancing portion. Under these
conditions the term “‘orientation”’ can have little meaning, and we can
hardly say that stimulation causes the body to become oriented in a
certain way. But stimulation does determine the direction of motion,
and anything like orientation that can bé distinguished is a result of the
direction of motion, not its cause. Under stimulation the direction of
movement is changed first, then in consequence the animal takes an
elongated form which furnishes the only possible basis for the use of the
term “orientation.”

In the fact that to produce directed movement, local action of the
stimulus on a certain part of the body is necessary, causing local contrac-
tion or extension, the conditions in Amoeba agree with the fundamental
postulates of the tropism theory. The agreement is most precise in the
positive reactions, where the part stimulated is the part that extends
and determines the direction of movement. In the negative reactions

a,

270 BEHAVIOR OF THE LOWER ORGANISMS

e agreement with the theory is less complete; for while the part that
‘contracts is determined by the region stimulated, the extension and
consequent direction of movement are, as a rule, not thus determined.

be But while some important features of the behavior of Amoeba are
iN yagreement with the underlying assumptions of the tropism
is certain that for such organisms alone the theory would never
proposed. The facts for Amoeba can be formulated in a
pler way than by bringing in the conception of orientation, —
ion derived from organisms with permanent body axes, and
ly these.

‘when we turn to an examination of the behavior of those uni-
cellular organisms having permanent body axes, we find the conditions
widely at variance with the assumptions of the local action tropism

“theory. In the infusoria most of the behavior is quite inconsistent with

the theory. The reactions are not determined by the direct action of
a localized stimulus in producing greater contraction’ or extension in
that part of the body on which it impinges. The organism_responds
as a whole, by a reaction involving all parts of the body. It does not
necessarily turn directly toward_or_directly-away from the source of
stimulation, as would be the case if it reacted in accordance with this
tropism theory. The direction of turning is determined by internal
factors; the animal turns toward a side which is structurally defined.
For inducing directed motion it is not necessary that the stimulus should
act differently on different parts of the body. The cause of reaction —
that is, of a change in the movements — is usually a change from one
condition or intensity to another. Thus the essential point in deter-
mining ‘Whether reaction shall occur is in most cases the direction of
movement — whether this takes the organism (or its most sensitive
portion) away from, or toward, the optimum. It is difficult to conceive
a type of behavior more completely opposed to the local action theory
of tropisms above set forth.

In some cases this method of reaction produces orientation with
relation to the direction of some external force, in other cases it does not.
The orientation when it occurs is brought about through continued

}movements that are varied in direction, with final selection of one of
these directions. Whether orientation shall or shall not result. depends
on whether it must result in order that there shall be a cessation of the
stimulation which is producing the varied movements. These relations
have been set forth in detail in our account of the behavior of Paramecium

° (Chapter IV, Section 6), so that it is not necessary to take them up here.

To almost all the relations set forth in the preceding paragraphs

there is one exception. In the reaction of ciliate infusoria to the electric

THE TROPISM THEORY 271

current we find certain features which agree with the local action tropism
theory. These features are so striking and so utterly at variance with
everything found in the remainder of the behavior of these organisms
that they throw into strong relief the contrast between the usual behavior
and the requirements of this tropism schema. Owing to the remarkable
cathodic reversal of the cilia (a phenomenon not paralleled under any
other conditions), the motor organs of opposite sides or ends of the
ciliate infusorian act under the electric current in different ways. The
result is behavior partly in accordance with the tropism schema. This
furnishes us with a picture of what behavior would be if this schema
held throughout. The unity and codrdination that are so striking in
the remainder of the behavior are here quite lost._ Different parts of
the motor organs urge the organism in different directions at the same
‘time. The animal seems to be trying to do two opposed things at once
‘(see p. 89). Nothing more ineffective and unpurposive can be imag-
ined than such behavior. But in producing these local effects the elec-
tric current is unique among stimuli, and the reaction is as far from
_the typical behavior of these organisms as can be imagined. The elec-
tric current may be used for producing local contractions in man as
well as in Paramecium, but such contractions cannot be considered an
adequate type of the behavior of mankind. The electric current never
acts effectively on the organisms under the natural conditions, so that
normally they never show the peculiar behavior produced by it. To
all the natural conditions of existence they react in a totally different
manner — a manner quite at variance with this tropism schema.

In the bacteria-as-in-the-infusoria the behavior is not in accordance
with the above-discussed_ theory of tropisms. The details of the re-
actions are not so completely known as in the infusoria. But what we
know shows that the behavior of these organisms so far as involved in
the directed reactions is as follows: When stimulated the bacterium
changes its course, moving in some other direction, — a direction de-4
termined_by_its_own_body_ structure, and not by the position of the
stimulating. agent.

Thus we find in the unicellular organisms very little in the behavior
that can be interpreted in accordance with this local action theory of
tropisms. ‘The latter does not by any means express the fundamental
nature of their behavior in directed reactions. ‘These are based chiefly
on the performance under stimulation of varied movements, with selec-
tion from the resulting conditions, — the “method of trial.”

In the symmetrical Metazoa we of course find many cases in which
the animal turns directly toward or away from a source of stimulation,
without anything in the nature of preliminary trial movements. This

272 BEHAVIOR OF THE LOWER ORGANISMS

is a simple fact of observation, which leaves open the possibility of many
different explanations. Is the simple explanation given by the local
action theory of tropisms one that is of general applicability to the
directed reactions of lower and higher Metazoa?

In considering the evidence on this question, we find that even in
symmetrical Metazoa the direction of movement with reference to ex-
ternal agents is by no means always brought about by a simple, direct
turning. On the contrary, in many of the Metazoa, trial movements are
as noticeable and important as in the Protozoa. This we have illustrated
in detail for many invertebrates in the section devoted to this subject
(Chapter XII, Section 2). For such behavior the local action theory
of tropisms fails to give determining factors.

In some cases the turning movements are directly toward or from
certain stimuli. But the question here is, whether this turning is pro-
duced by the local action of the agent in question on the part of the
body against which it impinges, as is asserted by the theory which we
are considering, and illustrated in Fig. 144.

In a few instances this is apparently the case. The medusa escapes
unfavorable stimulation by contracting most strongly on the side on
which the stimulus impinges. In Hydra local stimulation by chemicals,
heat, or electricity often produces limited local contraction, causing the
animal to bend toward the side stimulated. In various sea anemones
the tentacles, and sometimes the body, may bend toward the side stimu-
lated, as this theory demands. Yet this direct contraction plays very
little part in the behavior of these animals. In Hydra it is only injurious
agents to which the animal responds in this way, and the result is to still
further subject the animal to the action of the injurious agent. In order
to escape the action of injurious stimuli, Hydra has recourse to behavior
of quite a different character, and in its natural life there seems to be
no indication that behavior ever occurs in accordance with this theory
of direct local action. In sea anemones the direct turning toward the
region stimulated is at once supplemented by movements determined in
quite a different way, — through the structure of the organism, — the
tentacles bending toward the mouth. Without this supplementary re-
action the local bending would be of no service. In the hydroid Cory-
morpha it is only this second method of bending that occurs at all.
Throughout the Ccelenterata the part played by trial movements, not
directly determined by the position of the stimulating agent, is most
striking and important.

In the echinoderms we have, as in Amceba, organisms which are
as a rule without a definite body axis, so far as the direction of locomo-
tion goes; there is usually no permanent anterior, posterior, right, or

THE TROPISM THEORY 273

left. Hence a theory like that of tropisms, based primarily on the posi-
tion or orientation of the body axis with reference to the direction of
the stimulating agent, can find little precise application. Yet it is again
in this group that we find behavior that is in certain respects at least in
accordance with the tropism theory. For locomotion in a certain direc-
tion the stimulus must be localized, acting in a different way on the two
sides; this is one of the postulates of the tropism theory. Further, a
local stimulation may have at least a partially local effect, and this may
result in movement in a certain direction. But as v. Uexkiill has well
pointed out, the elementary factors here are the typical reaction methods
(“‘reflexes’’) of the individual organs of the body surface. The tropism,
if we attempt to apply the concept at all, is a mere collection of these
elementary reactions; it is not in any sense itself an elementary factor.
In other words, the tropism theory would never have been based on the
known behavior of the echinoderms, for the facts, even so far as they
agree with the fundamental postulates of the theory, can be formulated
more directly and simply in another way. The tropism theory is fur-
nished with an apparatus of relations that finds no application to the
starfish and sea urchin.

Furthermore, as we have shown in detail, much of the behavior of
these animals is based on the method of trial. In such bilaterally sym-
metrical animals as the flatworm Planaria we have the most favorable
possible conditions for action on this tropism theory, and such animals
often do turn directly toward or away from sources of stimulation. But
when this occurs, is it due merely to the local contraction or extension
of the musculature on the side on which the stimulus impinges, or is it
a reaction of the animal as a whole?

This question can be answered only by a thorough’ study of all the
factors in the reaction; such a study is given us for the flatworm by
Pearl (1903). The positive reaction of the flatworm — the direct turn-
ing toward the source of stimulation — seem to present ideal condi-
tions for explanation on the simple tropism theory. But Pearl, after
exhaustive study, concludes that the processes in the reaction are as
follows : —

“A light stimulus, when the organism is in a certain definite tonic
condition, sets off a reaction involving (1) an equal bilateral contraction
of the circular musculature, producing the extension of the body; (2) a
contraction of the longitudinal musculature of the side stimulated, pro-
ducing the turning toward the stimulus (this is the definitive part of the
reaction); and (3) contraction of the dorsal longitudinal musculature,
producing the raising of the anterior end. In this reaction the sides do
not act independently, but there is a delicately balanced and finely co-

od

274 BEHAVIOR OF THE LOWER ORGANISMS

ordinated reaction of the organism as a whole, depending for its existence
on an entirely normal physiological condition” (Pearl, 1903, p. 619).

Similar lack of uniformity and simplicity appears in the remainder
of the behavior of the flatworm. In few of the lower metazoa has the
movement been so thoroughly analyzed as in Planaria. But there seems
to be no reason for thinking that in this simple animal these relations are
more complex than in most invertebrates.

The recent thorough studies of R4dl (1903) on reactions to light in
many animals have shown clearly the inadequacy of this theory to ac-
count for most of the reactions to this agent. Bohn (1905) has likewise
been compelled to reject this theory, on the basis of the results of his
thorough studies on the behavior of the animals of the seashore. To
the writer it appears that most of the recent thorough work on animal
behavior points in the same direction.

We must then conclude from our examination of the facts that for
the lower organisms taken into consideration in the present work, the
local action theory of tropisms is of comparatively little value for inter-
preting behavior. This theory uses and attempts to make of general
application certain elements here and there observable in the behavior
of some organisms. But in many organisms even these elements are
almost completely lacking, and in no organism that we have taken up
does this theory adequately express the nature of behavior. The tro-
pism as applied to animal behavior in the sense we have considered, is
not an elementary factor; it is only a more or less artificial construction,
made by combining certain elements of behavior and omitting others
that are of most essential significance. It makes use of certain simple
phenomena that actually exist, but elevates these into a general explana-
tion of directed behavior, for which they are utterly inadequate. The
prevalence of this local action. theory of tropisms as a general explana-
tion of behavior in lower organisms is based only on an incomplete knowl-
edge and an insufficient analysis of the facts of behavior.

OTHER TERMS EMPLOYED IN ACCOUNTS OF ANIMAL BEHAVIOR

In the foregoing pages we have criticised a certain definite theory of
tropisms, this being the theory most commonly implied when the word
is used in a precisely defined way. But the term “tropism” is often
used in a looser sense. By some writers the word is applied merely to
the general phenomenon that the movements of organisms show definite
relations to the location of external agents. In this sense the word im-
plies no theory, and is not open to criticism on the basis of observed
facts. It is, of course, equally applicable to the behavior of man and

THE TROPISM THEORY 275

that of lower organisms; in this sense the botanist Pfeffer (1904, p. 587)
consistently remarks that a man who bends toward a lighted window
shows phototropism as does a plant. The use of the word in this purely
descriptive sense is often convenient, but we need to keep in mind the
fact that the word thus used involves no explanation, and includes phe-
nomena of the most heterogeneous character.

By some writers the word “‘ tropism’ is restricted to the bending or
inclination of a fixed organism, while the movements of free organisms
under the influence of external agents are called taxis. This distinc-
tion is a purely descriptive one. =

Some writers reserve the term “ tropism ” (or taxis) for those reactions
in which the organism takes up a well-defined orientation with relation
to the line of action of some external agent. Other reactions, in which
orientation is not a feature, are variously designated as kinesis (Engel-
mann, 1882 a; Rothert, 1901; Garrey, 1900), as -pathy (Davenport,
1897; Yerkes, 1903 0; and others), as -metry (Strasburger, 1878; Olt-
manns, 1892), and by various other names, depending on the method
by which the author in question considers them to be brought about.
On this basis the reactions of infusoria to water currents, gravity, the
- electric current, and to light coming from one side would be called
tropisms or taxis; while the reactions to chemicals, osmotic pressure,
heat and cold, and mechanical stimuli would be designated by some
other term.

An immense number of technical terms have been devised for appli-
cation to the phenomena of behavior in the lower organisms. A system-
atic exposition of a very complete set of such terms will be found in the
paper of Massart (1901). The “Plant Physiology” of Pfeffer (1904)
likewise deals extensively with this matter. A proposed new terminol-
ogy applying to many of the features of behavior is set forth by Beer,
Bethe, and v. Uexkiill (1899). A number of other references to this
matter will be found in the literature list at the end of the present chapter.

As to the value of giving technical names to every distinguishable act
that an organism performs, opinions will differ. So far as the names
are purely descriptive, expressing nothing more than some observed
action of the organism, it is difficult to see any very great advantage in
their use. ‘To say that an organism shows phobism (Massart), is merely
to say that it moves backward; to say that it reacts by dorsoclinism
(Massart), is the same as to say that it reacts by turning toward the dorsal
side. To most readers the latter expressions are more intelligible than
the former, and they are equally accurate and complete. Such purely
descriptive terms embody no results of scientific analysis. Their use is
therefore merely a question of convenience or taste on the part of the

276 BEHAVIOR OF THE LOWER ORGANISMS

writer. They are doubtless at times convenient and may perhaps be
used to advantage.

So far as the terms involve a certain explanation of the phenomena,

their use requires that the writer shall accept that explanation for the
phenomena in question, otherwise their use gives rise to misconception.
This makes many of the terms unavailable, save in a very restricted
degree. The study of behavior seems hardly to have reached as yet
the stage where a hard and fast nomenclature can be used to advantage.
To the present writer, after a long-continued attempt to use some of the
systems of nomenclature devised, descriptions of the facts of behavior in
the simplest language possible seems a great gain for clear thinking and
unambiguous expression. If investigators on the lower organisms would
for a considerable time devote themselves to giving in such simple terms
a full account of behavior in all its details, paying special attention to
the effect of the movements performed on the relation of the organism
to the stimulating agent, this would be a great gain for our understanding
of the real nature of behavior, and some theories now maintained would
quickly disappear. Less attention to nomenclature and definitions, and
more to the study of organisms as units, in their relation to the environ-
ment, is at the present time the great need in the study of behavior in
lower organisms.

LITERATURE XIV

A. The local action theory of tropisms: LOEB, 1900, 1897; VERWORN, 1895,
1899; DAVENPORT, 1897; DRIESCH, 1903; RADL, 1903; HOLT AND LEE, 1901 ; MEN-
DELSSOHN, 1902 @; GARREY, 1900; BOHN, 1905 ; JENNINGS, 1904 ¢.

B. Nomiendlatute and classification in behavior: PFEFFER, 1904 ; MASSART, I9gOI ;
BEER, BETHE, AND V. UEXKULL, 1899; NAGEL, 1899; CLAPAREDE, 1905; HABER-
LANDT, 1905; ZIEGLER, 1900; NUEL, 1904; DAVENPORT, 1897; ROTHERT, I9OI ;
ENGELMANN, 1882 a; LOEB, 1893, 1900 ; GARREY, 1900; STRASBURGER, 1878;
OLTMANNS, 1892 ; YERKES, 1903 0.

CHAPTER XV

IS THE BEHAVIOR OF THE LOWER ORGANISMS COMPOSED OF
REFLEXES? ,

THE simplest reaction of an organism is the performance of a definite
simple act in response to a definite stimulus. Such is the contraction of
Vorticella, such the reversal of movement in a bacterium or in Para-—
mecium or the flatworm. A simple responsive action of this sort isf
commonly known as a reflex. The question has been raised as to
whether the behavior of the lower organisms differs from that of higher
animals in being purely reflex or not; in other words, whether all their
reactions to stimuli are reflexes. For various organisms this question is
answered by many authors in the affirmative. In some cases the be-
havior of animals much higher in the scale than most of those we have
considered is characterized as purely reflex. This is v. Uexkiill’s view
for the sea urchin. We must examine briefly the question whether
behavior in these lowest organisms is properly characterized as reflex.

What is a reflex? The concept of reflex action has had a complex
origin, and as a result it is defined in various ways. One of the phe-

}: . on which the concept is based is the contraction of a muscle
when a certain nerve is stimulated. The stimulation is supposed to pass
from the nerve to the spinal cord, whence it is reflected back to the mus-
cle; hence the name reflex. Some authors hold that the term can be
properly used only of acts thus performed by the aid of the nervous
system. This would of course exclude reflexes from the behavior of
unicellular organisms, and introduce uncertainty in dealing with the
lower Metazoa, for in many of these we do not know whether the re-
actions are throughout mediated by the nervous system or not. But it
is more usual to consider the reflex as a certain type of action, without
regard to the particular anatomical structures involved. Even where
the term is limited to actions produced through the nervous system, some
other term is employed to indicate the corresponding type of action in
animals without a nervous system, so that the existence of a particular
kind of action, indicated usually by the word “ reflex,” is recognized.
Thus, Beer, Bethe, and v. Uexkiill (1899) use for reflexes performed
without a nervous system the word “‘antitype.” We may then ex-

277

‘

278 BEHAVIOR OF THE LOWER ORGANISMS

amine the reflex (or antitype) simply as a type of action, without regard
to the existence of a nervous system.

A second phenomenon on which the concept of reflex action is based
is the following: In ourselves, certain acts are performed unconsciously.
These acts have been considered identical with those due to the passage
of an impulse from the nerve-ending to the spinal cord, and thence back
to the muscle; that is with reflexes. Hence the reflex is often defined
as an unconscious or involuntary action: “Such involuntary responses we
know as ‘reflex’ acts’’ (James, “ Psychology,” Vol. I, p. 13). “ Reflexes
are voluntary acts that have become mechanical” (Wundt). This defi-
nition of a reflex act as involuntary or unconscious is widely employed. §
If we accept this definition, there is of course no way by which we can
tell whether the reactions of lower animals are reflex or not. By obser-
vation we cannot tell whether the reacting organism is conscious, for
this would require, as Titchener (1902) says, an objective criterion of
the subjective, — an objective criterion of that which is not objective,
and this is impossible. It is certainly as dogmatic and unscientific to
assert that the actions of organisms are reflex in the sense of uncon-
scious, as to assert the opposite, for we have no knowledge on this
point. We can recognize reflex acts, from this point of view, only in
ourselves.

A third phenomenon on which the conception of a reflex is based is

he supposed uniformity of certain reactions. The muscle responds to
all sorts of stimuli by contracting. This uniformity is considered by
many authors the essential feature in reflexes. Hobhouse (1901, pp. 28,
29) defines reflexes as “‘uniform responses to simple stimuli.” Accord-
ing to Beer, Bethe, and v. Uexkiill (1899, p. 3), reflexes are reactions
“always recurring in the same manner.’”’ Driesch (1903) says a reflex
is ‘a motor reaction which as a response to a stimulus occurs the first
time completely and securely.”

This objective definition of a reflex as an invariable reaction to a
simple stimulus is the only one which we can really use in determining
by means of objective study whether the behavior of animals is reflex
in character. Is the behavior of lower organisms composed of reflexes
in this sense?

Possibly the best case for an affirmative answer to this question could
be made out for the bacteria. Here there is so far as known only one
form of motor reaction, — the reversal of movement when stimulated.
But even in the bacterium the uniformity is disturbed by the fact that
on coming in contact with a solid the organism sometimes comes to rest
against it, while at other times it reacts by the reversal of motion. Owing
to their minuteness, the behavior of these organisms is less known than

_

REFLEXES IN BEHAVIOR 279

that of other unicellular forms, so that it is difficult to make a positive
generalization on such a point as the present one.

If we attempt to apply our definition of a reflex to the behavior of
the infusoria, — of Paramecium, for example, — we at once get into
difficulties. The “avoiding reaction” of Paramecium is sharply limited
in many ways, and always takes place in accordance with a definite type.
But it is far from being invariable. The reaction is composed of three
factors, which may vary more or less independently of each other, in
such a way that an absolutely unlimited number of combinations may
result, all fitting the generalized type. ‘The possible variations may be
summed up as follows: If the animal be taken as a centre about which
a sphere is described, with a radius several times the length of the body,
then as a result of the avoiding reaction the animal may traverse the
peripheral surface of this sphere at any point, moving at the time either
backward or forward. In other words, the reaction may carry it in any
one of the unlimited number of directions leading from its position as a
centre. While the direction of turning is absolutely defined by the struc-
ture of the animal, yet the combination of this turning with the revolu-
tion on the long axis permits the animal to reach any conceivable position
with relation to the environment. In other words, Paramecium, in spite
of its curious limitations as to method of movement, is as free to vary its
relations to the environment in response to a stimulus as an organism
of its form and structure could conceivably be. Such behavior does not
fall within the concept of a reflex, if the latter is defined as a uniform
reaction.

Still less does the behavior of Stentor yield itself to formulation as
purely reflex. To the same stimulus, under the same external conditions,
this animal may react, as we have seen, in several different ways; its
reaction depends upon its physiological condition. The same is true
for Hydra and other Ccelenterata, for the echinoderm, the flatworm, and
many other invertebrates, as we have set forth in detail in the descrip-
tion of the behavior of these organisms. In the sea anemone we have
examples of indecision, parts of the positive reaction being combined
with parts of the negative. In all these cases the behavior is far from.
that sureness and fixity that characterizes the supposed reflex.

Even in Ameeba it is difficult to apply the reflex concept to the be-
havior. So far are the reactions here from being uniform, that we can
almost say, on the contrary, that Amoeba never does the same thing
twice. The behavior is here formless, undefined, not held within nar-
row bounds by structural conditions, as in the infusoria and in most
higher animals; the essential criteria of reflex action seem lacking. It
would be very difficult to apply the reflex concept, for example, to the

280 BEHAVIOR OF THE LOWER ORGANISMS

behavior of a floating Amoeba in attaining a solid support, as described
on page 8, or to the food reaction illustrated in Fig. 21. Further, as
we have seen on page 20, Amoeba may at different times react in oppo-
site ways to the same stimulus.

Indeed, consideration shows that it is impossible to apply rigidly the
conception of a reflex, as an invariable reaction to a definite stimulus,
to the behavior of any organism having more than one motor reaction
at its command. James (‘‘ Psychology,” Vol. I, p. 21) and Pearl (1903,
p- 704) have given us sketches of what would be the behavior of an
organism whose acts were purely reflex. Taking the reaction to food
as an example, James says: “The animal will be condemned fatally and
irresistibly to snap at it whenever presented, no matter what the cir-
cumstances may be; he can no more disobey this prompting than water
can refuse to boil when a fire is kindled under the pot. His life will
again and again pay the forfeit of his gluttony. Exposure to retaliation,
to other enemies, to traps, to poisons, to the dangers of repletion, must
be regular parts of his existence. His lack of all thought by which to
weigh the danger against the attractiveness of the bait, and of all voli-
tion to remain hungry a little while longer, is the direct measure of his
lowness in the mental scale”? (/.c., p. 21). Such a picture has only to
be presented to make us see the impossibility of constructing the entire
behavior of an organism out of such irresistible reflexes. For the re-
actions to dangers and enemies must then be reflexes, as well as the
reactions to food, and the two are incompatible. Suppose the food and
the danger are present together, as often happens. The organism can-
not react fatally and irresistibly to both, for the movements required are

in opposite directions. It must decide to react either with relation to On

one or to neither, and in either case the fatality and irresistibility of at
least one of the reflexes disappears.

If, then, we consider the reflex an invariable reaction to a given stimu-
lus, we cannot hold that behavior in lower organisms is made up of
reflexes. Indeed, the fact that stands out most clearly in the behavior
is the following: Each stimulus causes as a rule not merely a single
definite action that may be called a reflex, but a series of ‘‘trial’’? move-
ments, of the most diverse character, and including at times practically
all the movements of which the animal is capable. The reaction to a
given stimulus depends on the physiological state of the organism, not
alone on its anatomical structure; and physiological states are variable.
This is true both for the infusoria and for man.

The attempt to characterize the behavior of the lower organisms as
purely reflex has risen from the desire to show that the structural con-
ditions of the organism and the physical and chemical action of the

REFLEXES IN BEHAVIOR 281

stimulus are sufficient to account for their behavior, without the neces-
sary intervention of consciousness. This is well expressed by v. Uexkiill
(1897, p. 306) when he says that we are to regard the reflex as ‘the
necessary course of a process that is conditioned by nothing else than
the mechanical structure of the organism.”’ Shall we include the phys-
iological state of the organism as part of its mechanical structure? If
we answer this question in the negative, then it is clear that the behavior
of the lower organisms is not reflex in character. If on the other hand
we answer this question in the affirmative, holding that the physiological
state is some chemical or physical configuration of the substance of the
organism, and therefore to be included in its mechanical structure, then
the entire question concerning the reflex character of behavior in a given
organism loses its objective character and evaporates into thin air. For
in the highest as well as the lowest organism the reactions must be sup-
posed to depend upon the physical and chemical constitution of the
organism, unless we are to accept vitalism. And if when we say that
the behavior of an organism is reflex in character, we mean only that
its behavior depends upon its physical and chemical make-up, we can
make no distinction upon this ground between the behavior of lower
and higher organisms. ‘This point is indeed well recognized by thought-
ful psychologists. ‘‘The conception of all action as conforming to this
[the reflex] type is the fundamental conception of modern nerve physi-
ology,” says James (“Principles of Psychology,” Vol. I, p. 23). Those
who have been most strenuous in attempting to demonstrate that the
behavior of certain lower organisms is “‘ purely reflex”’ in character would
probably be the last to hold that in the higher organisms behavior must
be explained on essentially different principles. The attempt often
made to contrast the behavior of lower organisms as reflex with that
of higher organisms as something else, seems therefore a shortsighted
and pointless proceeding. What a given organism does under stimu-
lation is limited by its action system, and within these limits is deter-
mined largely by its physiological condition at the time stimulation
occurs. In the lowest organism the action system confines the varia-
tions in behavior within rather narrow limits, and the different physio-
logical conditions distinguishable are few in number; hence the behavior,
is less varied than in higher animals. But the difference is one of degree,
not of kind. The behavior of Paramecium and the sea urchin is reflex
if the behavior of the dog and of man is reflex; objective evidence does
not indicate that there is from this point of view any fundamental differ-
ence in the cases.

The importance attributed to the concept of reflex action is of course
due to the desire to find a simple invariable unit for behavior, compa-

282 BEHAVIOR OF THE LOWER ORGANISMS

rable to the atom in physics. To obtain such a unit it is necessary to take
into consideration as an additional possible variable, the physiological
state of the organism. Dr. E. G. Spaulding has suggested the follow-
ing: We cannot properly say for a given organism ‘same stimulus,
same reaction,” as appears to be the usual idea of a reflex. On the
other hand we can say ‘“‘same physiological state, same stimulus, same
reaction,” and this supplies whatever need there may be for a simple
invariable element of behavior. To this element the term “reflex” or
an equivalent one might be applied, and we might then maintain that
the behavior of all organisms is made up of reflexes. But on this defi-
nition the question whether the behavior of a given organism is made
up of reflexes is not a problem for objective investigation; but the con-
ception that it 7s thus made up is a postulate, in accordance with
which we interpret the results of our observations; and this applies to
the highest as well as to the lowest organisms. The assumption that
varied physiological states exist is of course one of these interpretations,
made to save what is essentially this very postulate, — the principle
that like causes always produce like effects.

LITERATURE XV

REFLEXES AND BEHAVIOR

HOBHOUSE, 1901; JAMES, 1901; BEER, BETHE, AND V. UEXKULL, 1899; TITCH-
ENER, 1902; DRIESCH, 1903; V. UEXKULL, 1897.

CHAPTER XVI
ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS

1. THE CAUSES AND DETERMINING FACTORS OF MOVEMENTS AND
REACTIONS

In the following sections we shall analyze the behavior of the lower
organisms described in previous chapters, attempting to determine the
essential characteristics of behavior and to bring out the chief factors
of which it is made up. We shall take up first the factors causing or
determining the movements and reactions, treating first the inner, then
the outer, factors. ‘Then we shall consider the movements and reactions
themselves, attempting to bring out the features of essential importance.
From a synthesis of our results on both sets of factors — the causes and
the effects — we shall try to arrive at a general statement of the funda-
mental character of behavior in the lower organisms.

The external factors in behavior are usually known as stimuli, and
their effects on movement as reactions. The term “ reaction” has been
used in various ways. In our analysis we shall employ the word “‘reac-
tion” as’ signifying an actual change in movement. The word is some-
times used in a looser sense. For example, the movement toward a
source of light is often spoken of as the reaction to light, even though the
only observable change of movement was that by which orientation was
brought about. This looser sense is sometimes unavoidable, either from
our ignorance of the facts, or for other reasons; when used in this loose
sense in the following, the context will clearly indicate it. Where ques-
tion might arise, reacton is to be understood as meaning an observable
change of movement. To avoid ambiguity, the latter phrase will some-
times be used in place of the word ‘‘reaction.”” The following discussion
will be intelligible only if this meaning of the word “reaction” is kept in
mind.

A. The Internal Factors

(1) Activity does not require Present External Stimulation. — A first
and essential point for the understanding of behavior is that activity
occurs in organisms without present specific external stimulation. The

283

284 BEHAVIOR OF THE LOWER ORGANISMS

normal condition of Paramecium is an active one, with its cilia in rapid
motion; it is only under special conditions that it can be brought partly
to rest. Vorticella, as Hodge and Aikins (1895) showed, is at all times
active, never resting. The same is true of most other infusoria and, in
perhaps a less marked degree, of many other organisms. Even if external
movements are suspended at times, internal activities continue. The
organism is activity, and its activities may be spontaneous, so far as
present external stimuli are concerned.

The spontaneous activity, of course, depends finally on external
conditions, in the same sense that the existence of the organism depends
on external conditions. ‘The movements are undoubtedly the expression
of energy derived from metabolism, The organism continually takes
in energy with its food and in other ways, and continually gives off
this energy in activities of various sorts. The point of importance is
that this activity often depends more largely on the past external
conditions through which the energy was stored up than upon present
ones. Thus the organism may move without the present action of
anything that may be pointed out as a specific external stimulus to
this movement.

This fact is of great importance for understanding behavior, and
many errors have arisen from its neglect. If we see an organism moving,
it is not necessary to assume that some external stimulus now acting is
producing this movement. In studying the reactions to present particu-
lar stimuli, as light or gravity or a chemical, it is in many cases not
necessary to account for the fact of movement, for the movement comes
from the discharge of internal energy, and often the organism was moving
(though perhaps in another direction) before the stimulus began to act.
It is only the change in the movement when the stimulus acts that the
present stimulus must account for. In the movement of Paramecium
toward the cathode, it is not necessary to assume, as some have done,
that a special force (as cataphoric action) is required, to carry the ani-
mals. They were moving equally before the electric current began to
act; the difference that the stimulus has made is in the direction of
motion, and it is only this that the stimulus must account for. In the
movements of infusoria toward chemicals, some have supposed that an
attractive force from the chemical was necessary, actually bearing the
organisms along; this is quite superfluous. In general, when an
organism moves toward or away from any agent, it is unnecessary to
assume that an actually attractive or repellent transporting force is act-
ing upon it. Often — perhaps usually in the lower organisms — move-
ment in a certain direction is due only to the release of inhibition. The
organism moves in the given direction because it is moving from internal

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 285

impulse, and because movement in this direction is not prevented.
This possibility must be considered in all cases.

Further, when the action of a stimulus actually changes the direction
of movement in an organism, persistence in this new direction by no
means demands persistence in stimulation. The new direction once
attained may be followed, from the internal impulse to movement,
merely because there is nothing to change this direction, or because
stimulation does occur when this direction is changed, bringing the
organism back to it. This is apparently the case, as we have seen, in
the reactions of infusoria to gravity, to water currents, and to light com-
ing from a certain direction.

Often, of course, stimulation does rouse an organism to increased
activity. But even in this case the activity is due to the release of in-
ternal energy. It may, therefore, continue long after the stimulation
which inaugurated the release has ceased to act. Such continuance
thus does not necessarily imply continued action of the stimulus. In
many cases the specific stimulus to action is only the change of conditions.
Thus, if light or a chemical acts upon an organism, the only stimulus
may be the sudden change, even though the organism continues to
move after the conditions have become constant. Whether the effective
stimulation actually continues, must be determined by experiment; it
cannot be simply assumed.

In general, when an organism is moving in a certain way — even
when toward or from a certain agent — careful analytical experimenta-
tion is necessary to determine whether this movement is due to present
stimulation, or to the simple outflow of the stored-up energy of the or-
ganism through’'the channels provided by its structure. In most cases,
apparently, the latter is true.

The spontaneous activities of the organism — those not due directly
to present specific external stimulation — are, perhaps, the most im-
portant factors in its behavior.

(2) Activity may. change. without..External.Cause. — If we watch a
specimen of Vorticella under uniform conditions, we find that its behavior
does not remain uniform. At first the animal is outstretched, its cilia
bringing a current of water to the mouth. After a certain period its
stalk contracts, its peristome folds inward, and its cilia cease moving.
Soon it extends and resumes its normal activity. These alternations of
different ways of behaving occur at rather regularintervals, though the ex-
ternal conditions remain unchanged. Hydra shows parallel changes of
behavior at intervals, under uniform external conditions (p. 189); the
medusa contracts at intervals, though there is no change in the outer con-
ditions, and similar examples could be given for many other organisms.

286 BEHAVIOR OF THE LOWER ORGANISMS

(3) Changes in Activity depend on Changes in Phasialagical States. —
What causes the changes in behavior described in the foregoing para-
graph? Since the external conditions have not changed, the animal
itself must have changed. The Vorticella which contracts and folds its
cilia is in certain respects a different animal from the one that remains
extended and keeps its cilia in active motion, otherwise it would not act
thusdifferently. Its internal or physiological condition has been changed.
Soon its original condition is restored; it unfolds and behaves as it did
at first. In the same way, the physiological condition _of the Hydra
that stands quiet with outspread arms is different from that of:
which, without external cause, .contracts.and.changes.its_position. / The
behavior produced by these differences in physiological condition is the
same as that producible by an external stimulus.

Other examples of changes in behavior due to changed physiologi-
cal states are shown in the different reactions of hungry and of
well-fed individuals, which we have seen in so many cases, and in the
different reactions of organisms as determined by their respiratory
processes.

The precise nature of these internal_changes.of_.condition_we—of
course do not know. The expression “physiological states” evidently
includes a great many things of heterogeneous character, having merely
the common characteristic that they are internal modifications of the
living substance resulting in changed behavior. In the lower organisms
it is difficult to define the different classes of physiological states in an
objective way, though the progress of investigation will doubtless make
this possible. Certain fundamental differences in diverse states will be
pointed out in the following pages.

(4) Reactions-to-External--Agenis.depend-on Physiological States. —
Change of activity is, of course, often produced by external agents.
With this point we are to deal later; here what interests us is the fact
Mat io any given organism the reaction to a Siven_ external agent de-
pends on the physiological condition of the organism. This principle.

is of such | importance that we must dwell upon it.

—

aE ee

depends" upon the ‘progress of of " the : metabolic processes. To a given
external condition the nature of the reaction often depends upon whether
it favors these metabolic processes. If material for these processes is
lacking, the reaction to stimuli is of such a character as to secure such
material. In such organisms as the ccelenterates almost the whole
character of the behavior, down to the details of the reactions to specific
stimuli, depends thus on the condition of the processes of metabolism
(see Chapter XI). The behavior of organisms is similarly determined

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 287

by the course of other internal processes; these are, perhaps, the most
important factors determining physiological states.

Of a somewhat different character are the changes in physiological
state exemplified in the behavior of Stentor and the flatworm. In Sten-
tor, as we have seen. in Chapter X X, we can distinguish at least five differ-
ent physiological states in which the same.individual reacts differently
‘to the same conditions. Under stimulation by numerous grains of car-
mine in the water, the Stentor in condition No. 1 does not react at all.
In condition No. 2 it reacts by turning into a new position. In condition
No. 3 its reaction is a reversal of the ciliary current. In No. 4 it responds
by contracting at brief intervals. In No. 5 the contractions are stronger
and the organism remains longer in the contracted condition, finally
breaking its attachment to its tube and swimming away. Throughout
this entire series of reactions the external conditions remain the same, _
so that we can attribute the different reactions only to different condi-
tions of the organism. ee er Ss

In the flatworm we have seen in Chapter XII that six different physio-
logical conditions may be distinguished, in each of which the flatworm
is a different animal, so far as its reactions to stimuli are concerned.
We need not repeat the details regarding these conditions here. Illus-
trations of the fact that the reaction of the organism depends on its
physiological state might be drawn from the behavior of many other
animals.

(5) The Physiological State.may..be changed by. Progressive Internal
Processes, particularly those of metabolism. The well-fed sea anemone
or Hydra is a very different animal, so far as its behavior is concerned,
from the specimen that has fasted. Under uniform conditions, the sea
anemone that is well fed remains quiet; while the individual_that has
exhausted the material for metabolism toils painfully.away_on_a_ tour of
exploration. The well-fed individual reacts negatively or not at—all
to that to which the hungry individual reacts positively. The Para-
mecium bursaria that has exhausted its supply of oxygen behaves in one
way with regard to light, the individual i in which respiration is progress-
ing normally in another way. y. Innumerable examples illustrating this
principle can be found in the behavior of lower and higher organisms.
It is hardly too much to say that the progress of the metabolic and other
physiological processes is the chief factor in determining the behavior
of lower organisms.

(6) The Physiological State may be changed by the Action oj External
Agents. — This follows directly from the behavior of"Stentor’and the
flatworm, to which we have referred in the preceding paragraph. The
Stentor in condition No. 1, as we have seen, does not respond to the

288 BEHAVIOR OF THE LOWER ORGANISMS

stimulus of the carmine grains in the water. The stimulus continues,
and after a time the physiological condition changes so that the animal.
does respond. The change in physiological state can then be due only
to the action of the stimulus. In the same way the other changes in the
physiological condition of of Stentor and the flatworm are evidently due
largely, at least, to the continued action of the stimulus.
(7) The Physiological State may be changed by the Activity of the
a bs. — This is demonstrated by the spontaneous changes in the
behavior of Vorticella or Hydra, of which we have already spoken. At
first the animal is in a certain condition which corresponds to extension
and activity. It then passes into a condition which results in ‘contrac-
tion. But it does not remain contracted; the contraction itself restores
the original condition, so that the animal now again extends and becomes
_active. Certain of the changes in physiological state seen in Stentor
and the flatworm are probably due to the reactions of the organism.
Thus, we find that the flatworm, after turning for a long time away from
a lateral stimulus, suddenly changes and turns in the opposite direction
(p. 253). The change of physiological state conditioning this change of
reaction was probably due, not alone to the continuance of the stimu-
lus, but to the previous prolonged turning of the flatworm in a certain
direction.
(8) External Agents cause Reaction by changing the Physiological
\ssate of the Organism. — We have found that external stimuli cause
changes in physiological state, and that changes in physiological state
induce changes in behavior, — activities of a definite character. It is
evident, then, that external agents must change the behavior of organisms
by changing their physiological condition. In other words, in a reaction
to an external stimulus the course of events is probably as follows:
The stimulus causes first a change in the physiological condition of the
organ or organism. This, then, causes a change in behavior, which
we call a reaction to the stimulus. What the organism reacts to is
the change produced within it by the external agent. Hence, if two
different external agents induce the same internal change (as by block-
ing certain processes) they will receive the same reaction.
(9) The Behavior of the Organism at any Moment depends upon its
PPhysiological State at that Moment. — This follows immediately from
the principles already developed. We have seen that both in ‘“spon-
taneous”? movements and in reactions to stimugethe behavior depends
on the physiological condition of the animal. The behavior must then
depend, secondarily, not only upon the present external stimulus, but
upon all the conditions which affect the physiological states. This
point will be developed under the two succeeding heads.

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 289

| (10) Physiological States change in Accordance with Certain Laws. —
It is evident that we may distinguish at least two great classes of physio-
logical states, — those depending on the progress of the metabolic

ge cst qargeneper ptr momar pera - The changes
in the metabolic states, as we may call the former, of course depend largely

ee EL REED DES AEM

upon the laws of metabolism. In the physiological states not directly
dependent on metabolism, but rather upon stimulation and upon the
activity of the organism, such as we have seen in Stentor, we find certain
fairly well-defined laws of change, of a peculiar character.

In a number of organisms we have found the following phenomenon:
Under certain conditions the organism reacts in a certain way. These
conditions continuing, the organism changes its first reaction for a second
or third or fourth. Later the same external conditions recur, and now
the organism at once responds, not by its first reaction, but by its final
one. This is illustrated for unicellular organisms by the case of Stentor
(Chapter X); for higher Metazoa it is well seen in the behavior of cer-
tain Crustacea, as described by Yerkes and Spaulding (Chapter XII).
There are certain differences in these two cases that will be taken up
later.

How does this state of affairs come about? The “physiological
state” is evidently to be looked upon as a dynamic condition, not as
a static one. It is a certain way in which bodily processes are taking
place, and tends directly to the production of some change. In this
respect the “law of dynamogenesis,” propounded for ideas of movement
in man, applies to it directly (see Baldwin, 1897, p. 167); ideas must
indeed be considered, so far as their objective accompaniments are con-
cerned, as certain physiological states in higher organisms. The changes
toward which the physiological state tends are of two kinds. First..the

physiological state.(like.the idea) tends to produce movement. This

movement often results in.such.a. change of conditions as destroys the
physiological state under consideration.. But in case it does not, then

the second tendency of the physiological state shows itself. . It tends to
resolve itself into another and different state. Condition 1 passes to
condition 2, and this again to condition 3. This tendency shows itself
even when the external conditions remain uniform.

In this second tendency a most important law manifests itself. hen

takes place quickly and spontaneously. ~ :

his may be illustrated from the behavior of Stentor, as described

in Chapter X as follows: When the organism is stimulated by the flood
U

290 BEHAVIOR OF THE LOWER ORGANISMS

of carmine grains (or in any other way), this produces immediately a
certain physiological state (corresponding to that accompanying a sensa-
tion in ourselves); this state we may call A. This state at first produces
no reaction. As the carmine continues or is repeated, this state A passes
to a second state B, producing a bending to one side. (The two may
differ only slightly, but a difference must exist, otherwise B would not
produce a reaction while A does not.) After several repetitions of the
stimulus, the condition B passes to the condition C, producing a reversal
of the cilia, and this finally passes to D, resulting in a contraction of the
body. The course of.the changes in physiological states may then be
represented as follows : —

A—_B—C—_D

Now we find that after many repetitions of the stimulation the or-
ganism contracts at once as soon as the carmine comes in contact with
it. In other words, the first condition A passes at once to the condition
D, and this results in immediate contraction.

A—>D

It seems probable that the same series occurs as before, save that con-
ditions B and C are now passed rapidly and ina modified way, so that
they do not result in a reaction, but are resolved directly into D. The
process would then be represented as follows: —

A—>B’—>C’—> D

But whatever the intermediate conditions, it is clear that after the
state A has become resolved, through pressure of external conditions,
into state D, this resolution takes place more readily, occurring at once
after the state A is reached.

The same law is illustrated in the experiments of Yerkes and Spauld-
ing on much higher organisms. In the experiments of Spaulding
with the hermit crabs (Chapter XII), the introduction of the screen and
the diffusion of the juices of the fish cause the animals to move about.
In so doing they reach the dark screen, which induces, let us say, the
physiological condition A. This leads to no special reaction. But
this is followed regularly by contact with food, inducing the physiological
condition B, which is concomitant with a positive reaction. The physio-
logical condition A is thus regularly resolved into the condition B.
In the course of time this resolution becomes automatic, so that as soon
as the condition A is reached it passes at once to B. The positive reac-
tion concomitant with B is therefore given even though the original cause
of B is absent.

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 291

In the experiments of Yerkes, using the two passages to the water,
described in Chapter XII, the following are the conditions. The pres-
ence of the investigator or the drying of the animal at T, Fig. 139, acts
as a stimulus to cause movement away from JT. A turn to the right is

accompanied, let us say, by the physiological condition A. This is
soon followed by contact with the glass plate G, inducing the condition
B, which involves inhibition of movement and a turn in another direction.
In the course of time the condition A comes to be resolved immediately
into B, so that movement is inhibited at the start. On the other hand, the
physiological condition C, concomitant with a turn to the left, is regularly
resolved into the condition D, concomitant with reaching the water, and
inducing a positive reaction. This resolution becomes automatic, so
that the turn to the left is followed at once by forward motion to
the water. In these cases the actual number of physiological states
that could be distinguished is, of course, greater than what we have
set forth above. But this does not alter in any way the general
principle involved.

The law of the resolution of physiological states illustrated in the
foregoing examples is of the highest importance for the understanding
of behavior. With selection from among varied movements, it forms
one of the corner-stones for the development of behavior. The law
may be expressed briefly as follows: —

The resolution of one physiological state into another becomes easier
bn more rapid after it has taken place a number of times. Hence the

ehavior primarily characteristic for the second state comes to follow
immediately upon the first state.

The operations of this law are, of course, seen on a vast scale in higher
organisms, in the phenomena which we commonly call memory, asso-
ciation, habit formation, and learning. In the lower organisms the mani-
festations of this law are comparatively little known. This is probably
due largely to difficulties of experimentation. Since the law has been
demonstrated to hold in unicellular organisms (Stentor and Vorticella),
there is much reason to suppose that it is general, and that it will be
demonstrated in one form or another for other lower organisms. ‘There
seems to be no theoretical reason for supposing it to be limited to higher
animals. Very great differences exist among different organisms as to
the ease with which the quick resolution of one physiological state into
another is established. There are likewise great differences in the per-
manency of existing connections among the present reaction methods.
Hence it does not follow, as Yerkes (1902) has well pointed out, that be-
cause a few experiments do not demonstrate this law in a given case,
the law, therefore, does not hold. In his experiments with crustaceans,

292 BEHAVIOR OF THE LOWER ORGANISMS

Yerkes found that a very large number of repetitions were necessary
before a given resolution was established.

(11) Different Factors on which Behavior Depends. — We have seen
bnat the behavior of the organism at a given moment depends on its
physiological state, and that it therefore secondarily depends upon all
the factors upon which the physiological state depends. Hence we can-
not expect the behavior to be determined alone by the present external
stimulus, as is sometimes maintained, for this’ is only one factor in
determining the physiological state. The behavior at a given moment
may depend on the following factors, since these all affect the physio-
logical state of the organism: —

1. The present external stimulus.

2. Former stimuli.

3. Former reactions of the organism.

4. Progressive internal changes (due to metabolic processes, etc.).

5. The laws of the resolution of physiological states one into another.

All these factors have been strictly demonstrated by observation and
experiment, even in unicellular organisms. Any one of these alone,
or any combination of these, may determine the activity at a given
moment.

CHAPTER XVII

ANALYSIS OF BEHAVIOR (Continued)

B. The External Factors in Behavior

(1) As we have seen in the foregoing chapter, external agents produce}
reactions through the intermediation of changes in the internal physio-
logical condition of the organism. ‘This proposition is, perhaps, a truism,
yet it needs to be kept in mind if behavior is to be understood. In the
following discussion it will be unnecessary to mention specifically in each
case the intermediate step in the process.

(2) The most general external cause of a reaction is a change in the |
conditions affecting the organism. ‘This has been illustrated in detail
in the descriptive portions of the present work. In most cases the change
which induces a reaction is brought about by the organism’s own move-
ments. These cause a change in the relation of the organism to the
environment; to these changes the organism reacts. The whole be-
havior of free-moving organisms is based on the principle that it is the
movements of the érganism that have brought about stimulation; the
regulatory character of the reactions induced is intelligible only on this
basis. Reactions due to stimulation produced in this manner are seen
when an organism progresses from a cooler to a warmer region, or vice
versa; when it moves into or out of a chemical in solution; when it
strikes in its course against a hard object; when the unoriented infuso-
rian shows lateral movements while subjected to light coming from one
side. In all these cases it is the movement of the organism which causes
a change in its relation to the external agent, and this change produces
reaction. In most, if not all, cases the change is one in the intensity of
some agent acting on the organism.

But an active change in the environmental conditions, not produced
by movement of the organism, may likewise produce reaction; this is,
of course, most frequently the case in fixed organisms, such as the sea
anemone. Responses produced in this way are seen in the reactions of
organisms when heated or cooled from outside, or when a chemical
or a solid object is brought in contact with them, or when the source
of light changes in intensity or position, or when the direction of a water

293

294 BEHAVIOR OF THE LOWER ORGANISMS

current changes. The general fact is that a change in the environment
produces a change in behavior.

A. Change of conditions often produces a change of movement when

either the preceding nor the following condition would, acting continu-

|

usly, produce any such effect. Thus when Euglena is swimming |

oward the source of light, if the light is suddenly diminished, the organism
reacts by a change in its course; it then returns to its course and continues
to swim toward the light as before. Its behavior before and after the
change is the same; but at the moment of change there is a reaction.
Paramecium may live and behave normally in water at 20 degrees or at
30 degrees, yet a change from one to the other, or a much less marked
change, produces a definite reaction. This relation could be illustrated
by many cases from the behavior of any of the organisms described in the
foregoing pages. Thus change simply as change may produce reaction.

To constant conditions, on the other hand, unless differing very
greatly from the normal, the organism usually does not react. The
Paramecium placed in ;4, per cent sodium chloride reacts at first, but
soon resumes its normal behavior. Euglena or Stentor when subjected
to changes in the illumination of the anterior end react till they come
into a position of orientation where these changes cease; they then swim
forward in the normal manner. As a general rule, organisms soon be-
come acclimatized to a continuous condition, if it is not too intense.
Exceptions to this rule will be considered later.

Of course a change must reach a certain amount before reaction is
produced; that is, there is a certain necessary threshold of stimulation.
In the best-known cases the amount of the change which produces re-
action is proportional to the intensity of the original condition; in other
words, the relation of stimulus to reaction follows Weber’s law (see pp.
38, 123). That is, it is relative change, not absolute change, that causes
reaction.

B. But not every change, even if sufficiently marked, produces

eaction. It is usually not change alone that determines reaction, but
change in a certain direction. Of two opposite changes, one usually
produces a certain reaction, while the other either produces none or
brings about a reaction of opposite character. This point is one that
is of fundamental importance for an understanding of behavior. It
may be illustrated in its simplest aspect from the behavior of the infusoria,
where any reaction that is produced is usually of such a character as to
remove the organism from the source of stimulation (the “avoiding
reaction’). Paramecium at a temperature of 28 degrees reacts thus
negatively to a change to a higher temperature, not to the opposite change.
Paramecium at 22 degrees reacts to a decrease of temperature, not to

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS = 295

an increase. Stentor reacts to an increase of illumination, not to a
decrease. Euglena when moderately lighted reacts negatively to a
decrease of illumination, not to an increase; if strongly lighted, it shows
the opposite relations. Paramecium reacts at passing into an alkaline
solution, but not at passing out; it reacts at passing out of a weak acid
solution, not at passing in. Hydra at 24 degrees reacts to an increase
of 2 degrees in temperature, not to an equivalent decrease. Innumerable
instances of this fact could be given from the behavior of the lower
organisms.

What decides whether a given change or its opposite shall produce
this negative reaction? Examination of the facts brings out the follow-
ing relations: The organism generally reacts by a change in its behavio
when the change is of such a nature as to lead away from the optimum
By optimum we mean here the conditions most favorable to the lif
processes of the organism in question. Changes leading toward this
optimum produce in many animals no reaction; the organisms simply
continue the activity which has brought about this change. Changes
leading away from the optimum produce a negative reaction, by which
the organism is removed from the operation of this change. There are
undoubtedly some limitations and exceptions to this, and with these we
shall have to deal later, but, as we have seen for Paramecium, it is un-
questionably the rule. Cases where this rule does not hold are striking
because exceptional. Reaction in this manner keeps the infusoria in
regions of moderate temperature, prevents them from entering injurious
chemical substances, brings green organisms such as Euglena into the
light, where their metabolic activities are aided, and in general keeps
the organisms in regions where the conditions are favorable. In these
organisms the chief cause of reaction to a change is its interference with
the normal life activities, and the reaction if successful serves to remove
the interference.

C. But in many cases changes which favor the normal ipesidi ed
produce reaction. The response is then of such a character as to retain
the organism under the conditions producing the change. Such re-
sponses we usually call positive reactions. In many cases it is clear that
such reactions are determined by a previously existing unfavorable
state of metabolism or of other processes. The Hydra or the sea
anemone does not react positively to food substances unless metabolism
is in such a state as to require more material; and parallel relations
exist in the behavior of many if not all organisms. In unicellular or-
ganisms definite positive reactions play a comparatively small part,
favorable conditions being secured primarily by a negative reaction to
less favorable conditions. It is possible that all positive reactions are

296 BEHAVIOR OF THE LOWER ORGANISMS

to be traced to this as the primitive type (see the following chapter).
That is, while the negative reaction is impelled by new unfavorable con-
ditions, tending to retain the more favorable old condition, the positive
reaction is impelled by the old unfavorable condition, tending to retain
the new more favorable one.

(3) Sometimes change of behavior occurs without change in the
nvironment, the external conditions remaining uniform. As a rule,

we have found that change of behavior occurs under uniform conditions
only when these are decidedly injurious to the organism. If the water
containing infusoria or the flatworm is heated to about 37 degrees, the
animals react not merely to the change in temperature; they continue
to react violently, with frequent alternations in the behavior, until they
die. Many examples could be given of such reactions. Under uniform
conditions a change in behavior also occurs at times owing to internal
changes. The commonest cases of this sort are the changes in behavior
due to hunger. In almost all cases of reaction under uniform conditions
we find that the reaction is due to some interference with the normal
life processes. But reactions under uniform conditions play only a
small part in the behavior, as compared with reactions to changes.

We have then two main results as regards the external causes of
changes in behavior: (1) change alone may produce reaction; (2) inter-
ference with the normal life processes or release from such interference
may produce reaction. The usual cause of a change in behavior is a
combination of both these factors — a change that hinders or helps the
normal life processes. In the lowest organisms it is chiefly interfering
changes that cause reaction.

(4) Reactions to Representative Stimuli.—In the reactions due to
hange, one further point is of much importance. The organism may
eact to changes that in themselves neither favor nor interfere with the
ormal life activities, but which do lead to such favor or interference.

The reaction given is then positive or negative in correspondence with
the benefit or injury to which the change leads. Thus, Stentor may
bend toward a small solid body when touched by it (Fig. 83), this reac-
tion aiding it to procure food, though there is no indication that the
touch itself is directly beneficial. Or it may contract away from a
light touch, this enabling it to escape from a possible approaching enemy,
though the touch itself is not injurious. Euglena reacts negatively
when its colorless anterior end alone is shaded, yet it is only when the
shadow affects its chlorophyll bodies that it interferes with metabolism.
The flatworm may turn toward a weak stimulus of any sort. This
leads in the long run to its obtaining food, though sometimes the
stimulus does not come from a food body. In such cases the animal

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 297

reacts positively merely to the localized change, not to the nature of
the change. Certain colorless infusoria, and the white Hydra, react
to light in such a way as to gather at the lightest side of the vessel
containing them. There is no evidence that the light itself is beneficial
to them, but their reaction does aid them in obtaining food, since their
prey gathers on the lightest side of the vessel. The collecting of Para-
mecia in CO, can hardly be considered to favor directly the life processes.
of the animals, but it apparently aids them to obtain food. The sea
urchin tends to remain in dark places, and light is apparently injurious
to it. Yet it responds to a sudden shadow falling upon it by pointing
its spines in the direction from which the shadow comes. This action
is defensive, serving to protect it from enemies that in approaching may
have cast the shadow. The reaction is produced by the shadow, but it
refers, in its biological value, to something behind the shadow.

In all these cases the reaction to the change cannot be considered
due to any direct injurious or beneficial effect of the actual change itself.
The actual change merely represents a possible change behind it, which
zs injurious or beneficial. The organism reacts as if to something else
than the change actually occurring; the change has the function of a
sign. We may appropriately call stimuli of this sort representative
stimuli. :

This reaction to representative stimuli is evidently of the greatest value,
from the biological standpoint. It enables organisms to flee from injury
even before the injury occurs, or to go toward a beneficial agent that is
at a distance. Such reactions reach an immense development in higher
animals; most of our own reactions, for example, are to such representa-
tive stimuli. Only as we react to actual physical pain or pleasure do we
share with lower organisms the fundamental reaction to direct injury or
benefit. Practically all our reactions to things seen or heard are such
reactions to representative stimuli. While such behavior plays a much
larger part in higher than in lower organisms, the existence of reactions
to representative stimuli even in the low organisms considered in the
present work is an evident fact.

How can we account for such reactions? It is perhaps worth while
to point out that the operation of the law of the resolution of physiologi-
cal states, set forth on page 291, would result naturally in the production
of such reactions. Let us take as the simplest possible case the reaction
of Euglena when its colorless anterior tip is shaded. Since it is only
the metabolism of the chlorophyll bodies that is blocked by shade, we
cannot suppose that the shading of the colorless tip actually interferes
with the life processes. Yet to this change Euglena reacts negatively.
We may suppose that the shading of this colorless part induces the indif-

298 BEHAVIOR OF THE LOWER ORGANISMS

ferent physiological state A, which of itself produces no reaction. But
this is invariably followed by the shading of the chlorophyll bodies,
interfering with metabolism and inducing the physiological state B, re-
sulting in a negative reaction. Thus the state A is regularly resolved
into the state B. In accordance with the law of the resolution of physio-
logical states, this resolution in the course of time becomes spontaneous.
A passes at once to B and a negative reaction occurs, even when the
colorless anterior tip alone is shaded. In unicellular organisms a condi-
tion so reached would naturally continue to succeeding generations, since
the organisms in reproducing merely divide.

In the same way the defensive reaction of the sea urchin when
shaded could be produced. The condition A, induced by the shade, is
usually resolved into the condition B, induced by the attack of an enemy,
and resulting in the defensive movement. This resolution in the course
of time may then become spontaneous, so that the sea urchin now reacts
defensively even when a cloud passes over the sun. This condition
could be continued to succeeding generations only if acquired charac-
ters are inherited.

Thus through the operation of the law of the resolution of physio-
logical states the following general result will be produced: If a given
agent induces a physiological state A, and this is usually followed by a
second state B, then in time the given agent will produce at once the
response due primarily to B. The organism will have come to react
to A as representative of B.

We do not know whether the development of reactions to representa-
tive stimuli has actually taken place in this way, or not. But the fact
that there is a factor, whose existence is demonstrated, that would pro-
duce exactly these results, certainly suggests strongly the probability
that they have been at least partly brought about in the way above set
forth. If the law of the resolution of physiological states is actually
operative throughout behavior, the effect would be to make behavior
depend on the results of the animal’s own action. This would produce
behavior that is regulatory, such as we actually find to exist. <

(5) The reaction to a given external stimulus depends, as we have
previously seen, on the physiological condition of the organism, not

lone on the nature of the external change. The physiological condi-
tion depends partly on whether the normal stream of life activities is
proceeding uninterruptedly. In certain physiological states, such as
hunger, the processes are not proceeding normally. This impels the
organism to a change, so that to almost any external stimulus it may
react in a way that tends to bring about a change. The hungry sea
anemone in this condition reacts positively to all sorts of neutral bodies;

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 299

the hungry Hydra reacts positively to chemicals. In certain physio-
logical conditions the flatworm reacts positively to almost any stimulus.
At other times the opposite conditions prevail; the animal reacts nega-
tively to the stimulus to which it before reacted positively. In closely
related organisms differing in their metabolic processes, the reaction to
a given agent depends on the nature of the metabolic processes, tending
to retain the conditions favoring these processes. This is especially
well illustrated in the bacteria (pp. 36, 39) and in the ccelenterates
(pp. 224, 231), but is equally true for other organisms. Thus what the
organism does depends on the course of its life processes, and upon the
completeness or incompleteness of their performance. In other words,
the behavior of the animal under stimulation corresponds to its needs,
and is determined by them. This correspondence is of course not al-
ways perfect; with this point we can deal after we have considered the
nature of the reactions given. But a study of the determining factors
of behavior demonstrates that the relation of external conditions to in-
ternal processes is the chief factor, and that hence behavior is regulatory
in essential nature.

(6) We may sum up the external factors that produce or determine
reactions as follows: (1) The organism may react to a change, even
though neither beneficial nor injurious. (2) Anything that tends to
interfere with the normal current of life activities produces reaetions of
a certain sort (‘‘negative”’). (3) Any change that tends to restore or
favor the normal life processes may produce reactions of a different sort
(‘positive’). (4) Changes that in themselves neither interfere with’
nor assist the normal stream of life processes may produce negative or
positive reactions, according as they are usually followed by changes
that are injurious or beneficial. (5) Whether a given change shall pro-
duce reaction or not, often depends on the completeness or incomplete-
ness of the performance of the metabolic processes of the organism
under the existing conditions. This makes the behavior fundament-

ally regulatory.

CHAPTER XVIII
ANALYSIS OF BEHAVIOR (Continued)
2. THe NATURE OF THE MOVEMENTS AND REACTIONS

In the preceding section we have dealt primarily with the causes and
conditions of movements and reactions; here we are to deal with the
movements and reactions themselves.

A. The Action System

Every organism has certain characteristic ways of acting, which are
conditioned largely by its bodily structure, and which limit its action
under all sorts of conditions. This perhaps seems a mere truism.
Ameeba of course cannot swim through the water like Paramecium, and
the latter cannot fly through the air nor walk about on dry land. But
the behavior of any given lower organism is actually confined in this way
within narrower limits than is frequently recognized. Formule have
at times been proposed to explain the movements of various organisms,
when the latter are incapable of performing the movements called for
by the formule. It is usually possible to determine with some approach
o completeness the various movements which a given organism has at
ommand. These form as a rule a codrdinated system, which we have
alled in previous pages the action system. The action system of an
rganism determines to a considerable extent the way it shall behave
nder given external conditions. Under the same conditions, organisms
of different action systems must behave differently, for to any stimulus
the response must be by some component of the action system. Thus,
Ameeba, the bacteria, Paramecium, Hydra, and the flatworm have ac-
tion systems of different character, and their behavior under given con-
ditions must differ accordingly. This matter has been dealt with in
detail in the descriptive portion of the present work, so that we need not
dwell upon it here. In studying the behavior of any organism, the first
requisite to an understanding is the working out of the action system.*

1 The action system corresponds largely to what Piitter (1904) calls the ‘ Symptoma-
tology”’ of organisms.

300

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 301

B. Negative Reactions

In our discussion of the causes of reaction we found that we could
classify most stimuli into two groups — those that interfere with the nor-
mal life processes, and those that do not. It will be best to consider
separately the reactions to these two classes of stimulation, and to take
up the reactions to unfavorable stimuli first, since these seem to present
the most primitive conditions.

The simplest reaction to unfavorable stimuli is merely a change in

| the direction or character of the movement. The organism is moving
in a certain direction; when subjected to an unfavorable change, it
changes its direction of movement. ‘This is the case in Ameeba, in bac-
teria, in infusoria, in rotifera, in the flatworm; indeed, in most free
organisms. The mere fact of a change is in itself regulatory or adap-
tive. The original behavior has brought on the unfavorable change,
hence the best thing to do is to change this behavior. If the unfavor-
able condition still persists, the behavior is changed again; this being
continued, the organism is bound to escape from the unfavorable condi-
tions if it is possible to do so. The repeated change in behavior under
unfavorable stimulation is very striking in Paramecium, in Stentor, in
Hydra, in the flatworm, and elsewhere.
- The fundamental principle for this method of reaction is that a
‘change of behavior under unjavorable conditions is in itself regulatory.
As we have before pointed out, the reactions of organisms are based on
the principle, usually correct, that it is the previous behavior of the
organism that has brought on the present conditions. Hence if these
conditions are unfavorable, a change of behavior is required.

The developments of this method of behavior found in different organ-
isms consist in defining, varying, and systematizing the changes that
occur. In Ameeba we find perhaps the simplest condition. When this
animal in its forward course meets unfavorable conditions it merely goes
in some other direction. In what direction it will go cannot be predicted
from either the structure of the organism or from the localization of
the stimulus, for Amoeba can move with any part in advance. It is evi-
dently determined by transient internal conditions. In organisms with
definite body axes and other structural relations, the change of motion
becomes more definite. In bacteria the organism moves after stimula-
tion in the opposite direction. In the free-swimming infusoria, as illus-
trated by Paramecium, and in the free Rotifera, there is an elaborate
system of movements which make the reaction effective. The animal
stops or reverses the movement which has brought on the unfavorable
condition, then swings its anterior end about in a circle as it moves for-

302 BEHAVIOR OF THE LOWER ORGANISMS

ward, so as to try successively many different directions. ‘The behavior
shows the “method of trial”? reduced to a system. It would be almost
impossible to suggest any modification of this reaction, as exemplified
in Paramecium, that would make it better fitted, under the given rela-
tions, for meeting all sorts of conditions. In fixed infusoria, such as
Stentor, this behavior is modified to adapt it to the fixed life. In the
free-swimming animal the organism is subjected to new conditions every
time the reaction is repeated, hence there is little occasion to try other
‘ methods of behavior. But if the organism is fixed in one place, this is
not true; when a given reaction is repeated it merely brings on the same
conditions its first performance induced. So different methods are de-
veloped. Under unfavorable conditions the organism first turns to one
side, then reverses its ciliary current, then contracts, etc. (see p. 174),
trying many different changes of behavior. In Hydra, in the starfish,
in the flatworm, we have seen this same “method of trial”? appearing
under various forms. In all these organisms persistent unfavorable
stimulation induces first one physiological state, then another, then
another, and to each state there corresponds a certain method of
behavior.

C. Selection from the Conditions produced by Varied Movements

In all this behavior we find the manifestations of a most. important
principle, one of far-reaching significance for the understanding of be-
havior. The stimulus does not produce directly a single simple move-
ment (a reflex act), of a character that relieves the organism at once
from the stimulating condition. On the contrary, stimulation is followed
by many and varied movements, from which the successful motion is
elected by the fact that it zs successful in causing cessation of stimula-
ion. This is the principle of the ‘selection of overproduced move-
ments,” of which much use has justly been made by Spencer, Bain, and
especially by Baldwin (1897, 1902), in attempting to explain behavior.
It is more accurate to speak of the selection of the proper conditions of the
environment through varied movements. It is primarily the proper en-
vironmental conditions that are selected; the movements are only a
means to that end. From this point of view what we have often called
in the foregoing pages the method of trial may be formulated as follows:
When stimulated the organism performs movements which subject it to
varied conditions. When in this way it reaches a condition that relieves
it of stimulation the reacton movement ceases, since there is no further
cause for it. The organism may then resume its usual movements. In
the case where the reaction consists of changes in direction, as in infuso-

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 303

ria, the resumption of the usual forward motion of course carries the
organism in a new direction brought about by the reaction.

What movements are produced by the stimulating agent depends
on the action system of the organism; it performs the movements that
it is accustomed to perform. In some cases these movements are of a
rather uniform character, yet are of such a nature as to subject the ani-
mal to many changes of the environmental conditions. This is the case,
for example in the reactions of such infusoria as Paramecium. In
other cases the movements themselves are varied; the organism first
reacts in one way, then in another, running thus through a whole series
of activities, till one succeeds in ridding the organism of the stimulating
condition. This is the method of behavior seen in Stentor and in most.
higher organisms. In both methods the essential point is the same
— the subjection of the organism to varied environmental conditions,
until one of these relieves it from the stimulation. This condition is
then said to be “selected.” In some cases the maintenance of this
favorable environmental condition involves continuance of the move-
ment finally resulting from the varied trial movements; in other cases
it does not.

Reaction by selection of excess movements depends largely on the
fact, previously brought out (p. 283), that the movement itself is not
directly produced by the stimulus. The movement is due, as we have
seen, to the internal energy of the organism. In the case of free-moving
animals like Paramecium, stimulation usually neither increases nor de-
creases the amount of motion, but merely causes it to change in various
ways. Reaction, of course, sometimes does take the form of an increase
of motion; this is seen in the increased movements of infusoria under
strong chemicals or heat; of Planaria under light, etc. But even in
these cases the energy for the-motion comes from within and is merely
released by the action of the stimulus. -It is important to remember, if
the behavior is to be understood, that energy, and often impulse to move-
ment, come from within, and that when they are released by the stimu-
lus, this is merely what James has called “trigger action.” There is
thus no reason to expect that upon stimulation an organism will perform
merely a single simple movement (a “reflex action’’), and then become
quiet. Movement of one sort or another is its natural condition, and
after stimulation has ceased it may show movements (the character or
direction of which may have been determined by the stimulus) for an
indefinite period.

Behavior by selection from the results of varied movements is based
on general principles. The reactions are not specific ones, definitely
adapted to particular kinds of stimulation, but are responses to amy

304 BEHAVIOR OF THE LOWER ORGANISMS

stimulation of a certain general character, — namely, to any condition
that interferes with the normal course of the life processes. On re-
ceiving an unfavorable stimulus that it has never before experienced,
the organism- behaving on this plan is not at a loss for some method
of reacting; it merely responds in the usual way, performing one move-
ment after another, till one of these relieves it of the stimulation, if this
is possible.

Of course special circumstances may arise in which this general
method of reacting may be ineffective. If dropped into a strong chemi-
cal, Paramecium reacts in the usual manner, though this does not help
it. If the water containing a flatworm is heated, the animal goes
through, one after the other, almost every reaction it has at command,
though all are unavailing (p. 245). The difficulty, of course, lies in the
fact that under these circumstances nothing the organism can do is of
any avail, and a man in similar conditions would be equally helpless.
The infusorian and the flatworm, like the man, merely try everything
possible before succumbing.

D. ‘“ Discrimination”’

The effectiveness of reaction by continued varied movements in
preserving the organism depends upon several factors. One of these is
what is called in higher animals the power of discrimination, — that is,

he accuracy with which the tendency to react is adjusted to the injuri-
usness of the stimulating agent. If an injurious agent resembles in
its first action a non-injurious one, so that the animal reacts in the same
way toward both, its behavior will not preserve it from injury. Using
the more subjective form of expression, if the organism does not discrimi-
nate between the first action of injurious and non-injurious agents, it
cannot react differently to them, until perhaps the injury has become
irremediable. The facts show that in both higher and lower organisms
the power of discrimination under weak stimulation is far from perfect.
Thus, in the sense in which we have used the term, Paramecium dis-
criminates acids from alkalies and salts, and these again from sugar.
But it does not effectively discriminate the first effects of different acid
substances, so that it swims into weak carbonic acid, which is harmless,
and likewise into weak sulphuric acid and copper sulphate, which kill it.
It does not discriminate the first action of a 10 per cent sugar solution
from that of water, hence it swims readily into the sugar solution and is
killed by the osmotic action. In all these cases it does discriminate and
react to the injurious agent when its effect has become marked, but
injury has then already occurred and the reaction does not preserve the

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 305

animal. In regard to these injurious substances Paramecium thus
makes what we would call in ourselves a “mistake.” The whole
scheme of reaction by the selection of the results of varied movements
is not a set, perfected, final one, but is a tentative plan, based on the con-
fusing world taken as it comes; it is liable to mistakes, and is capable of
development. Progress in this method of behavior takes place largely
through increase in the accuracy of discrimination of different stimuli.
This may occur through the law of the increased readiness of resolution
of physiological states after repetition, in the way that we shall attempt
to set forth later (Chapter XIX).

E. Adaptiveness of Movements

The second chief factor on which depends the effectiveness of
ehavior by selection of overproduced movements lies in the relative
tness of the movements to relieve the organism from the unfavorable
onditions. This, of course, depends on many things. If a powerful
hemical is diffusing from a certain direction, the rapid movements of

Paramecium are more likely to save than is the slow motion of Amzeba.
There are two factors on which the effectiveness of the movements
depends, that are worthy of special consideration.

In what we may call the pure method of trial, a most important re-

fuses for effectiveness is that the movements shall be so varied as
o give much opportunity for finding other conditions. There are great
differences in the behavior of different organisms from this standpoint.
This may be illustrated by a comparison of the reactions of Paramecium
and Bursaria to heat, as previously described. When a portion of the
area containing the organisms is heated, these two infusoria react in
accordance with essentially the same plan, yet practically none of the
Paramecia are injured, while a large proportion of the Bursarie are
killed. The difference is due chiefly to. the fact that Paramecium
rapidly repeats its reactions and revolves on its long axis as it turns, so
that in a short time it has tried in a really systematic way many different
directions, and is practically certain to find one leading away from the
heated region, if such exists. Bursaria, on the other hand, changes its
direction of movement only at longer intervals, and usually soon ceases
to revolve on its long axis as it turns toward the aboral side. This fail-
ure to turn on the long axis deprives it of the great advantage of being
directed successively in many different directions in the different planes
of space. The result is that it is likely to be destroyed by the heat
before it has found a direction leading to a cooler region.

306 BEHAVIOR OF THE LOWER ORGANISMS
F. Localization of Reactions

A second factor that is of great importance in making the move-
ments effective lies in the proper localization of the reactions. An
organism that moves directly away from an unfavorable agent (or di-
rectly toward a favorable one) has a great advantage over an organism
whose movements are not thus accurately directed. There are great
differences in different organisms in this respect; some react very pre-
cisely with reference to the position of the stimulating agent, while others
do not.

How is the relation of the reaction to the localization of the stimulus
brought about, and what is the cause of the differences between differ-
ent organisms in this respect ?

In answering this question, we can distinguish three different classes
of phenomena. These are the following: —

(x) First we have the simple phenomenon that when a portion of
an organism is stimulated this portion may respond by contraction, ex-
tension, or other change of movement. If the remainder of the body
does not respond, or responds in a different way, this gives at once a
reaction localized in a certain way with reference to the place of stimu-
lation. Such local responses we find in Amceba, where the part strongly
stimulated contracts, or if stimulated by a food body it extends. The
same phenomenon is found in Hydra, in the bending of the body when
one side is powerfully stimulated, in the bending of the tentacles of
Sagartia toward the point stimulated, and in the local contractions of
the medusa and of stimulated points on the body of the flatworm and
many other soft-bodied animals. The same thing is seen even in man
when the electrode of a battery is applied directly over a muscle; this
muscle now contracts. This seems a simple and primitive phenomenon,
and as such has been seized upon by the ‘‘tropism theory”? and made
the chief factor in the behavior of lower organisms, and particularly in
all directed reactions. As we have shown in our chapter on that theory,
this factor plays by no means the extensive part assumed by the theory,
and is quite inadequate to account for most of the behavior of lower
organisms. Even in the behavior of the organisms mentioned above,
where it clearly does play a part, this part is a subordinate one (see
Chapter XIV). In many organisms, such as the free infusoria and
some rotifers, it is hard to detect any part of the effective behavior that
is due to local reaction at the point stimulated. The fact that such
local reactions may and do occur in organisms is of course a fact of
much importance, but taken by itself it is utterly inadequate as a general
explanation of directed reactions.

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 307

the source of stimulation is brought about indirectly through selec-

‘tion from among varied movements. The organism tries moving in

"many directions, till it finds one in which there is no stimulus to further
change. In this way it may become oriented very precisely if the con-
ditions require. This is the prevailing method in the infusoria and in
various other organisms, as we have seen. It is becoming evident that
this method is more common even among higher organisms than has
been hitherto set forth. Movements of the head from side to side, such
as we find in the flatworm and many other animals, movements of the
eyes or other sense organs, such as are common in higher animals, or
movements of the body from side to side, as in the swimming of many
creatures, give opportunity for determining which movement tends to
retain the stimulus, which to get rid of it. In this way they form a basis
for the determination of the direction of locomotion through the method
of trial. How much part such movements play needs careful study.

(3) In still other cases the reaction shows a definite relation to the
localization of the stimulus, yet it is not due to local reaction of the part
stimulated, nor is it brought about by trial. If an infusorian is stimu-
lated at the anterior end it swims backward; stimulated at the posterior
end it swims forward. Both these movements are reactions of the
entire organisms, all the motor organs of the body concurring to pro-
duce them; they are not produced by local reactions of the organs at
one end or the other. The flatworm turns toward or away from the side
stimulated, by reactions involving the muscles of both sides, as well as
transverse and dorso-ventral muscles, all at a distance from the point
stimulated. If stimulated on the upper surface of the head, a compli-
cated twisting reaction occurs, involving many sets of muscles in vari-
ous regions (p. 273), by which the ventral surface is made to face the
stimulating agent (p. 236). Innumerable instances of this class of reac-
tions could be given; they include perhaps the greater number of the
directed movements of organisms. :

In these reactions a stimulus at one side or end evidently produces a
different reaction from a stimulus at the opposite side or end, though
the reaction is not primarily at the point stimulated. Doubtless the
stimulus starts a physiological process of some sort at the point upon
which it impinges, and this determines in some way the direction in
which the organism shall move. This effect in the region directly acted
upon corresponds to the “local sign” in human physiological psychol-
ogy. Behavior thus brought about is of course more effective than that
of the two preceding classes, permitting more direct and rapid reaction
than the method of trial, and meeting the conditions in an incomparably

(2) In many cases we find that the relation of the movement to

308 BEHAVIOR OF THE LOWER ORGANISMS

more adequate way than the simple local reaction of the part stimu-
lated.

Such behavior apparently represents not a primitive condition, but
a product of development. How has it been brought about?

It is evident that the operation of the law of the readier resolution of
physiological states after repetition, taken in connection with behavior
by selection from varied movements, would in course of time produce
such reactions. Let us suppose that the original reaction to a stimulus
at the anterior end was simply the production of a change resulting in
varied movements, according to the principles governing the actual
reactions of Paramecium. These varied movements would include for-
ward as well as backward motion. The forward movement would in-
duce still further stimulation, hence it would be changed. The back-
ward movement would give relief from stimulation, hence would not be
changed (till internal conditions require). Hence after stimulation at
the anterior end the physiological states induced will always be resolved
finally into that state corresponding to backward movement. This
resolution will in time become spontaneous; the physiological state due
to stimulation at the anterior end will pass at once into that producing
movement backward. Trial movements will no longer occur, but the
organism will respond at once by backward motion. A similar exposi-
tion will account, mutatis mutandis, for other localized reactions.

Whether this condition has been brought in the way above sketched
or not, its existence is evidently a fact of great importance. It is a step
forward from the pure “trial movement” condition. Wherever the or-
ganism can react in this manner, and this will meet the conditions
equally well, we may expect such behavior in place of repeated trials.
In higher organisms especially we find this behavior playing a large part.
Such organisms could not be expected, for example, to orient to gravity
or to light rays by trial movements, as the infusoria do, but rather to
turn directly toward or from the source of action of the stimulating
agent. This is, of course, known in many cases to be true.

But under many circumstances the reaction by trial is surer, though
less rapid, than that depending directly on the localization of the stimu-
lus, so that we find the trial method much used even by higher organ-
isms (see Chapter XII). Further, the more direct reactions due to pre-
cise localization are again combined as elementary factors to produce
behavior based on the method of trial, as when the flatworm turns toward
and “tries” any source of weak stimulation, accepting or rejecting it
finally, according as it proves fit for food or not. Thus we have be-
havior rising to a higher degree of complexity, — the method of trial in
the second or third degree, as it were. Examples of this character are
abundant.

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 3°09
G. Positive Reactions

We have thus far dealt primarily with reactions to environmental
conditions that interfere with the normal life processes. We find that
these induce changes in behavior, subjecting the organism to new con-
ditions, the more favorable one of which is selected. This gives us a
basis for the understanding of reactions toward conditions which favor
the normal life processes, — that is, positive reactions.

In conditions that are completely favorable —so that all the life
rocesses are taking place without lack or hindrance —there is of
ourse no need for a change in behavior, for definite reactions of any
ort. The most natural behavior on reaching such conditions, and that
vhich is actuaily found as a general rule among lower organisms, is a
ontinuation of the activities already in progress. These activities have

resulted in favorable conditions, hence it is natural to keep them up;
there is no cause for a change. This we find strikingly exemplified in
bacteria, infusoria, rotifers, and many other organisms under most
classes of stimuli. A change in behavior takes place only when the ac-
tivities tend to remove the organism from the favorable conditions.
Unfavorable conditions cause a change in behavior; favorable condi-
tions cause none. It is perhaps a general rule in organisms, high or
low, that continued completely favorable conditions do not lead to defi-
nite reactions. Of course while the external conditions remain the same,
the internal processes may change in such a way that these conditions
are no longer favorable, and now the behavior may change.

But when the organism is not completely enveloped by favorable
conditions, but is on the boundary, if we may so express it, between favor-
able and unfavorable ones, then there is often a definite change in the

ehavior leading toward the favorable conditions, —a positive reaction.
To understand such reactions, we may start from the fact that unfavor-
able internal conditions (as well as external ones) cause a change of
behavior. The Hydra or sea anemone whose metabolic processes are
interfered with by lack of material, exchanges its usual behavior for
activities of a totally different character, setting forth on a tour of ex-
ploration. It is a general fact that the hungry animal sets in operation
trains of activity differing from the usual ones. Interference with respi-
ration or with other internal processes has similar effects. An increase
of temperature above that favorable for the physiological processes like-
wise starts violent activities. Indeed, it is a general rule that changes
of internal condition unfavorable to the physiological processes set in
operation marked changes in behavior.
.But the activities thus induced are in themselves undirected, save

310 BEHAVIOR OF THE LOWER ORGANISMS

by structural conditions. There is nothing in the cause that produces
them, taken by itself, to specifically direct them with reference to exter-
nal things. Let us suppose, however, that certain of these movements
lead to a condition which relieves the interference with the internal
processes. The cause for a change of behavior is now removed, hence
the organism continues its present movement — continues in the direc-
tion, we will say, that has led to the favorable conditions. But perhaps
later — sometimes at the very next instant — this same movement may
tend to remove the organism from the favorable conditions — as when
a heated Paramecium passes across a small area of cool water, or a hun-
gry organism comes against food. Thereupon the cause for a change —
interference with the life processes — is again set in operation, and this
movement changes to another. Thus the animal changes all behavior
that leads away from the favorable condition, and continues that which
tends to retain it, so that we get what we call a positive reaction. The
change of behavior is due primarily in each case to the unfavorable
condition, internal or external — perhaps in last analysis always in-
ternal.

Behavior of this character is seen with diagrammatic clearness in
the free-swimming infusoria. These animals continue their movements
so long as they lead to favorable conditions, changing at once such move-
ments as lead away. They thus retain favorable conditions by avoiding
unfavorable ones; the positive reaction is seen to be a secondary result
of negative ones. :

In the infusoria we have then the most elementary condition of the
positive reaction. Let us now examine a more pronounced type of
positive reaction, — movement directly toward the favorable condition.
Ameeba flows toward and follows a food body with which it comes in
contact, as illustrated in Fig. 19, p. 14. Take, for example, its action
at 3 in this figure. It moves forward with broad front, part of the
movement taking it toward the food, part away. On coming in contact
with the food, all movement is changed which takes it away, only that
being retained which keeps the animal in contact with the food. We
have here then, as in infusoria, a case of selection from varied movements,
the central point being the changing of all motion that leads to less favor-
able conditions.

This is, perhaps, the fundamental condition of affairs, from which
all positive reactions are derived. The animal moves (partly or entirely
from internal impulse, as we have seen), but changes all movements that
lead to less favorable conditions. It therefore moves toward the favor-
able conditions. In many higher animals, even, this behavior is seen
in the random movements by which food is sought, by the aid of the

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 311

chemical stimulation which it sends forth. The movements leading to
loss of the favorable stimulation are changed, the others continued,
till the food is found (see p. 247).

But many animals have developed, in some way, as we have seen in
the account of the negative reactions, the power of localizing their reac-
tions precisely, so as to move in a certain definite way with relation to
the position of the source of stimulation. Let us suppose that such an
organism is reached by a favorable stimulus on one side — food, or the
optimum temperature. It has the power of turning directly toward this
favorable condition — and this, of course, is what happens in many
higher organisms. There is the same reason to think that this condition
is not primitive that we saw in the case of negative reactions. It may,
perhaps, be conceived as derived from behavior through selection of
overproduced movements in the way set forth on page 308. The precise
reactions shown in the actual taking of food are perhaps derivable in
the same way. :

In those animals whose positive reactions are precisely defined and
localized, there is, of course, the same evidence that the impulse to change
of behavior comes from within and is due to lack or hindrance of the
physiological processes, that we find elsewhere. If the metabolic pro-
cesses lack material for proper action, the medusa or sea anemone
changes its behavior and moves about, even though there is nothing
present to which it can react positively. When some object is reached,
whether there shall be a positive reaction or not depends again on the
state of the metabolic processes. If their state is bad, the animal re-
acts positively to almost anything; if fair, the animal reacts positively
to substances that will improve them; if they are in a completely satis-
factory condition, the animal does not react positively even to good
food.

Thus with all conditions absolutely favorable there will be no reac-
tion, either positive or negative. At the boundary between favorable
and unfavorable conditions, the animal moves in such a way as to retain
the favorable conditions. This is primitively due to selection from
varied movements — all movement leading to less favorable conditions
being changed. The “negative reactions’ thus seem to furnish in a
certain sense the primitive building stones from which the derived posi-
tive reactions are constructed. By development of the power of precise
localization of reactions, the derivation of the positive reaction in this
manner is in higher animals obscured. The fundamental fact for both
positive and negative reactions is that interference with the physiological
processes of the organism causes a change of behavior.

312 BEHAVIOR OF THE LOWER ORGANISMS

3. Résumé oF THE FUNDAMENTAL FEATURES OF BEHAVIOR

We have considered in the three foregoing chapters, first the deter-
mining factors of movements, and second the movements themselves.
Let us now attempt to put together the most important points in both,
so as to reach a general characterization of behavior.

The three most significant features of behavior appear to be (1) the
determination of the nature of reactions by the relation of external
conditions to the internal physiological processes, and particularly the
general principle that interference with these processes causes a change
in behavior; (2) reaction by varied or overproduced movements, with
selection from the varied conditions resulting from these movements —
or, in brief, reaction by selection of overproduced movements; (3) the
law of the readier resolution of physiological states after repetition. The
first of these phenomena produces the regulatory character of behavior.
The second and third furnish the mainsprings for the development of
behavior, the second being constructive, the third conservative.

The activity of organisms we found to be spontaneous, in the sense
that it is due to internal energy, which may be set in operation and even
changed in its action without present external stimuli. In reactions
this energy is merely released by present external stimuli. What form
the activity shall take is limited by the action system, and within these
limits is determined by the physiological state of the organism. Physio-
logical states depend on many factors. The two primary classes of
states depend on whether the internal life processes are proceeding unin-
terruptedly in the usual way. Interference with these processes produces
a physiological state of a certain character (“‘negative’’), while release
from interference or assistance to those processes produces a different
state (‘positive’). Within or beside these contrasted primary classes,
many subsidiary variations of physiological condition are possible, each
with its corresponding method of behavior; at least five of these have been
distinguished in a unicellular organism. Any change, external or in-
ternal, may modify the physiological state, and hence the behavior.

The effects of external agents depends largely on their relation to the
normal course of the life processes — whether aiding or interfering,
or neither. A primary fact is that interference with the life processes
produces progressive changes in physiological state, inducing repeated
changes in behavior. This is in itself regulatory, tending to relieve the
interference, whether due to internal or external causes; it is a process
of finding a reaction fitted to produce a more favorable condition. When
through such changes a fitting reaction is found, the changes in physio-
logical state and hence of behavior cease, since there is no further cause

ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 313

for change. In the same way a fitting reaction to a beneficial change,
or one releasing from interference, may be found. This fitting reaction
then tends to be preserved, by the law of the resolution of physiological
states, in accordance with which the physiological state inducing this
reaction is reached more readily after repetition. Thus the production
of varied movements by stimulation is the progressive factor in behavior,
while the law of the resolution of physiological states is the conservative
factor, tending to retain fitting reactions once attained.

Through the law of the resolution of physiological states behavior
tends to pass from the pure “‘trial”’ condition to a more defined state.
The operation of,this law tends to produce reactions precisely localized
with reference to the position of the stimulating agent; increased appro-
priate reaction to the first weak effects of injurious or beneficial stimuli;
and appropriate reactions to representative stimuli,-according as they
are followed by injurious or beneficial stimuli. In higher organisms
such defining of the reactions has gone far; much of the behavior con-
sists of derived reactions. ‘There are in such organisms doubtless other
factors producing derived reactions, besides the law just mentioned.
These are treated in our chapter on the ‘‘ Development of Behavior.”

Thus through the production of varied movements by stimulation
the organism finds the best method of behavior, and through the law
of the resolution of physiological states it tends to retain this method
as long as it is the best method. Through the same process it of course
tends to lose this method when it is no longer adapted to the conditions.
Thus behavior is regulatory in essential character; it is the process by
which the organism tends to find conditions favorable to its life processes
and to retain them, and it contains within itself the conditions for its
own more efficient development.

CHAPTER XIX
DEVELOPMENT OF BEHAVIOR

Iris not the primary purpose of the present work to treat the problems
of development, but rather to give an analysis of behavigr as we now find
it. But the results of this analysis furnish a certain amount of evidence
as to how development may have occurred; this it will be well to set
forth briefly. We shall consider first the development of behavior in
the individual, then its development in the race. In unicellular organ-
isms the first, perhaps, includes the second.

The primary facts for development in behavior are two principles
to which our analysis of the chief factors in behavior have led us. One
of these is that behavior is based fundamentally on the selection of varied
movements. The other is the law in accordance with which the resolu-
tion of one physiological state into another becomes readier and more
rapid through repetition.

In making use of the law of the readier resolution of physiological
states after repetition in the study of development, it needs to be kept
in mind that this law has been rigidly demonstrated for the lower organ-
isms only in scattered instances. It has been shown to be valid in cer-
tain unicellular organisms, but in these cases it has not been shown that
the modifications induced are lasting, as must be the case if this law plays
a part in the development of behavior. In the lowest metazoa the law
has likewise been demonstrated only for a few cases. In the flatworm
and the Crustacea we find the law clearly exhibited in the form that is
necessary in order that it may play a part in the permanent modification
of behavior.

On the other hand, the fact that the law remains undemonstrated
for many of the lowest organisms by no means indicates that it is not here
valid. We lack proper experiments to show whether it exists or not.
It is exceedingly difficult to carry out experiments that shall actually
test this matter in the lowest animals. The view that this law is univer-
sally valid in organic behavior is thoroughly consistent with all that we
know of the behavior of lower organisms, and the fact that it has actually
_been demonstrated in certain cases favorable for experimentation in
unicellular organisms raises a presumption of its general validity. The

314

DEVELOPMENT OF BEHAVIOR 315

following discussion of development is based on the assumption that the
law is one of general validity. It must be kept in mind that this zs
partly an assumption, but the probability that this will be found true
is such that the relation of development to the law is worth setting forth.
There is no other need greater in the study of animal behavior than
that of a thorough investigation of the validity of this law in the lower
organisms.

The question in which we are here interested is then the following:
How can behavior develop? That is, how can it change so as to become
more effective — more regulatory?

(1) The behavior of any organism may become more effective
through an increased tendency for the first weak effects of injurious or
beneficial agents to cause the appropriate reaction; in other words,
through increased delicacy of perception and discrimination on the part
of the organism. Such a change would be brought about through the
law of the readier resolution of physiological states after repetition.
When the organism is subjected to a slight stimulus, this changes its
physiological state, though perhaps not sufficiently to cause a reaction.
Such a slight stimulus would be produced by a very weak solution of a
chemical, or by a slight increase in temperature. Now, suppose that
this weak stimulus, causing no reaction, is regularly followed by a
stronger one, as would be the case if the weak chemical or slight warmth
were the outer boundary of a strong chemical solution, or of a region
of high temperature toward which the organism is moving. This
stronger stimulus would produce an intense physiological state, corre-
sponding to a marked negative reaction. That is, the first (weak)
physiological state is regularly resolved by the action of the stimulating
agent into the second (intense) one, inducing reaction. In time the
first state would come to resolve itself into the second one even before
the intense stimulus had come into action. As a result, the organism
would react now to the weak stimulus, as it had before reacted only to
the strong one. It would thus be prevented from entering the region
of the chemical or the heat, even before any injury had arisen.

(2) In the same way the organism may come to react positively or
negatively to a stimulus that is in itself not beneficial nor injurious, but
which serves as a sign of a beneficial or injurious agent, because it regu-
larly precedes such an agent. Suppose that a slight decrease in illumina-
tion (a shadow), which is of itself indifferent, regularly precedes the ap-
proach of an enemy, as happens in the sea urchin. The slight decrease
in light induces a certain physiological state, which is so little marked
that in itself it produces no reaction. But through the immediately
following attack of the enemy, this indifferent physiological state is

316 BEHAVIOR OF THE LOWER ORGANISMS

regularly resolved into an intense one, corresponding to a strong negative
reaction. Then after many repetitions of this process the indifferent
state resolves itself at once into the intense one, and the animal reacts
at the change in illumination, before the enemy has reached it. This
tendency to react to ‘“‘representative’’ factors, rather than to those
which are in themselves beneficial or injurious, is, of course, immensely
developed in higher animals. All positive or negative reactions to things
merely seen or heard, which are not directly beneficial or injurious save
when brought into direct contact with the organism, are, of course, reac-
tions to such representative stimuli.

It is clear that neither the tendency to react to faint stimuli, nor that
to react to ‘“‘representative”’ factors will be increased, save as this is
required by the environment. If the indifferent stimulus is not followed
with some regularity by the powerful one; that is, if it does not really
introduce a powerful agent, then there will be no tendency for the or-
ganism to acquire a reaction to this indifferent stimulus, for there will
be no regular resolution of the first (faint) physiological change into the
second (intense) one. And of course it would be no advantage, but on the
contrary a positive disadvantage, for the organism to acquire this ten-
dency to react to a// weak stimuli. If it reacted negatively to every slight
change in the environment, its movements would be seriously impeded ;
continued locomotion in any one direction would be almost impossible,
and its activity would be frittered away in useless and disconnected reac-
tions. The behavior becomes modified, in accordance with the prin-
ciples above set forth, only as it is to the advantage of the organism that
it should be so modified; that is, only as the modification favors the
normal current of life activities.

(3) Progress takes place through increase in the complexity and
permanence of physiological states, and in the tendency to react to these
derived and complex states, instead of to the primitive and simple ones.
We may imagine an organism whose physiological state depends entirely
on the stimulus now acting upon it, the organism returning completely,
as soon as the stimulus ceases, to its original state. Such an organism
could react only with relation to the present stimulus, and its reaction to
the same stimulus would always be the same. We might even imagine an
organism that could change in only one way under the action of stimuli;
its reactions to all stimuli would be the same. Such organisms would
represent a purely reflex type of behavior. An advance on this condi-
tion would be represented by cases where the physiological state induced
by a stimulus endures for a short time, influencing the immediately
succeeding reactions, and a further advance when the reaction performed
by the organism influences its physiological state, and therefore its later

DEVELOPMENT OF BEHAVIOR 317

reactions. Other advances would come in the production of different
physiological states according to the different organs or parts of the body
stimulated; this condition would naturally arise as structural differen-
tiations were developed in the body. As new organs develop and the
body becomes more complex, each part will naturally have physiological
states peculiar to itself, and will be acted upon by external stimuli,
producing changes in its physiological states. This is evidently the case
in such organisms as the sea urchin and sea anemone. These partial
physiological states of the different organs will then interact, altering
each other and combining to form a general state for the entire organism.
All the partial physiological states will be regulated, as in the separate
organism, by their relation to the normal life current of the organ con-
cerned, and further, their combinations will be regulated by their rela-
tion to the general life current of the organism. Whatever interferes
with this normal life current will be changed, while that which does
not interfere must persist. The partial and general physiological
states will be subject to the laws of the combination and regulation of
physiological states, just as in simple organisms. They will tend to
discharge themselves in action, or by resolution into other states, as in
the simple organisms. Thus the behavior of the organism must become
in time controlled by these physiological states, derived from many
sources besides that of the present stimulus. Behavior is gradually
emancipated from its bondage to present external conditions, and de-
pends largely upon the past experience and present needs of the organism.
This is the condition we find in higher animals, and especially in man.

The various stages set forth above are merely logical divisions, and
probably do not correspond in any close way to actual stages in the de-
velopment of behavior. There seems to be no reason to suppose that
an organism ever existed in which the original state is immediately
restored on the cessation of a stimulus. This immediate return to the
original state is not what we should expect from analogy even with inor-
ganic substances.’ Even in unicellular organisms we find a consider-
able complication of physiological states, depending on past stimuli,
past reactions, localization of the stimulus, and present external condi-
tions, as well doubtless as upon other factors.

Progress along the line just set forth will be brought about by the
same factors, whatever they may be, that determine the development

1 With relation to colloids, the substances of which organisms are mainly composed,
a high authority in physical chemistry remarks as follows: “Their qualities often
depend in the clearest way upon the former history of the colloid, its age, its previous
temperature, and the time this continued: in short, on the way it has reached its present
condition” (Bredig, 1902, p. 183). ‘The facts of behavior in organisms might be cited
as illustrations of this statement.

318 BEHAVIOR OF THE LOWER ORGANISMS

of complexity in structure. Differentiation of structure and of physio-
logical states must go hand in hand. It is not our province to attempt
to account for structural differentiations. The problem is the general
problem of evolution.

(4) Progress in behavior may take place through increased variety
and precision of the movements brought about by stimulation. Certain
kinds of movements are much better adapted to relieving an organism
from an unfavorable stimulation or securing it a favorable one than are
others. This is illustrated by a comparison of the reactions of Amoeba
and Paramecium, or of the reaction of Bursaria to heat with that
of Paramecium, as set forth on page 305. Owing to the difference in
the effectiveness of their movements, if an area containing equal num-
bers of Paramecia and Bursaria is heated at one end, many of the
Bursariz are killed, while all the Paramecia escape.

New and better adapted methods of movement may be acquired
through the selection of varied movements, in conjunction with the
law of the resolution of physiological states. Under strong stimula-
tion the organism, as it passes from one physiological state to another,
tries successively all the movements of which it is capable. One of
these movements (the spiral course, in the case of Bursaria) finally
removes the organism from the stimulating agent. This happens every
time the organism is stimulated in this manner. The result is that each_
physiological state is resolved into the succeeding one, until that one is
reached in which the organism responds by the effectual movement.
After a number of repetitions, this resolution takes place immediately,
in accordance with the law that after repeated resolutions of one physio-
logical state into another, this resolution takes place spontaneously and
rapidly. Thus the organism responds at once with the effectual move-
ment, and escapes.

In the same way the use of new organs might be acquired. Suppose
that an Ameeba sends forth, as sometimes happens, a long, slender pseu-
dopodium, which may vibrate back and forth, like a flagellum. When
stimulated, the overproduced movements of the organism, as it passes
from one physiological state to another, include the vibration of this
pseudopodium. Suppose that by this vibration the Amceba is at once
moved away from the stimulating agent — the pseudopodium acting as
does the flagellum in Euglena. If this is repeated, the physiological state
inducing other movements will always be resolved finally into that induc-
ing this one, and in time this resolution will take place so rapidly that
only this movement will come to actuality. The Ameeba will have ac-
quired the habit when stimulated of swimming by means of a flagellum.

Thus the behavior of organisms is of such a character as to pro-

DEVELOPMENT OF BEHAVIOR 319

vide for its own development. Through the principle of the production -
of varied movements, and that of the resolution of one physiological
state into another, anything that is possible is tried, and anything that
turns out to be advantageous to the organism is held and made permanent.

Thus through development in accordance with the two principles
mentioned, the organism comes to react no longer by trial, —by the over-
production of movements, —but by a single fixed response, appropriate
to the occasion. This is, of course, a great advantage, so long as the
conditions remain such as to make the response appropriate. Such
fixed responses are the general rule in the adult behavior of higher or-
ganisms, and are found to a certain extent in all organisms. In the
higher organisms we speak of some of these fixed responses as reflexes,
tropisms, habits, and instincts. The methods which we have discussed
are not the only possibilities for the development of such responses ; other
methods we shall take up later.

After the responses of the organism have become fixed, conditions
may so change that these responses are no longer appropriate. The
organism is then in a less advantageous position than one whose behavior
is determined more purely by trial movements. There will be now a
tendency for the fixed responses to become broken up and for processes
of trial to supplant them, until new fixed responses, appropriate to present
conditions, are produced. But in many cases the fixed responses are
so firmly established as not to give way save after long experience of
their lack of efficiency, and often the organism is destroyed by the new
environment, before it has developed appropriate responses by which
to preserve itself.

(5) We have thus far considered primarily the methods by which
the behavior of a given individual may be modified and made more
effective. It needs to be recalled that differences between the behavior
of different individuals may appear from other reasons. There are
congenital variations among different organisms. Some have naturally
a greater delicacy of perception or discrimination than others. Some
move more rapidly or in more or less varied ways than others, giving
some a more efficient method of reaction without any modification
through experience. These congenital variations play a most important
part in the question next to be considered.

(6) Our discussion thus far has related to individuals. The further
question arises as to how modifications of behavior may arise in the race
as a whole. How does it happen that the behavior of the race becomes
changed in the same way as that of the individual, so that succeeding
generations show the new method of reacting without acquiring it for
themselves ?

320 BEHAVIOR OF THE LOWER ORGANISMS

There seems to be no question but that the power of new individuals
to react in certain ways without preliminary trial has been much over-
estimated. In most organisms there is in the early stages of develop-
ment a continued process of trial, through which the habits become
established. On the other hand, there is no doubt that individuals do
appear with certain ways of reacting which most of their early ancestors
did not at the beginning have. The question as to how this happens,
therefore, presses for an answer.

The answer formerly given was, that the acquirements of the parent
are directly inherited by the offspring. The parent having come to
react in a certain way, the condition of the system inducing this reaction
is passed on to posterity. In the unicellular organisms there seems to
be nothing in the way of this inheritance by the offspring of the reaction
methods acquired by the parent. There is no distinction between germ
cells and body cells in these organisms; all acquirements pertain to the
reproductive cells. Through reproduction by division the offspring
are the parents, merely divided, and there is no evident reason why they
should not retain the characteristics of the parents, however these char-
acteristics were attained. If this is the real state of the case, then in
unicellular organisms the life of the race is a direct continuation of the
life of the individuals, and any acquirements made by the individuals
are preserved to the race.

But in multicellular organisms the facts show that in the immense
majority of cases the inheritance of the acquirements of the parents by
the offspring does not occur. We know that we do not start with the
education acquired by our parents, but must begin at the bottom, and
acquire both knowledge and wisdom of action. In other words, we
know that we fail to inherit directly the more efficient methods of reac-
tion acquired through experience by our parents, in at least nine hundred
and ninety-nine cases out of a thousand. Moreover, the theoretical
difficulties in the way of such inheritance are great, and no demonstrative
evidence seems to exist that it ever occurs. Thus we are certain that in
most cases it does not take place, and must doubt whether it is possible.

If we give up, as most students of heredity do, the inheritance of ac-
quired characters, the alternative explanation for progress in the race is
by natural selection of congenital variations. The theory of natural
selection may be stated briefly as follows: Organisms vary in many
ways, through variations affecting the germ cells. Among these varia-
tions are some that help the organism, making it more efficient in escap-
ing enemies or in obtaining food. These organisms, therefore, survive,
while those without these helpful variations are killed. The surviving
organisms transmit their helpful congenital variations to their offspring,

DEVELOPMENT OF BEHAVIOR 321

so that in time an entire race may show the characteristics which first
arose as accidental variations along with many other useless ones.

A great objection to this theory has been that it deals merely with
chance variations in all directions, so that progress along a definite line,
it is said, could never be brought about through it. The race progresses
just as the individuals do; what is first acquired by the individual is
later acquired by the race, as if the law of progress were the same in the
two cases. This, it is held, could not be brought about through the
selection of chance variations in all directions.

In recent years a most successful attempt has been made by J. Mark
Baldwin (1902) and others to show that this objection is not a valid one;
that the action of natural selection on characters playing a part in the
behavior would, in fact, be guided by laws similar to or identical with
those controlling the progress of the individual. To this guidance the
name organic selection has been given. Organic selection would then
account for the progress of the race in a continuous manner and in a
definite direction. We shall examine briefly, from this point of view,
the action of natural selection on behavior in the lower organisms.

Observation and experiment show that there exist such variations
in the behavior of lower organisms as would under certain circumstances
give opportunity for the action of natural selection. If into an area
containing Paramecia a drop of a Io per cent sugar solution is introduced,
most of the animals enter it and are killed, but a few react negatively
on coming in contact with it, and escape. If such solutions were a con-
stant feature of the environment, it seems probable that in time there
would be produced through selection a race of Paramecia that would
always react negatively to them, and would, therefore, not be endan-
gered by their existence. Similar differences exist among different indi-
viduals as to sensitiveness to other chemicals, to heat, and to electricity,
as we have seen in previous pages. There is thus undoubtedly an oppor-
tunity for the action of natural selection to produce a race of organisms
more sensitive to weak stimuli than is the average at present, if the en-
vironment should require it. But if the environment does not require it,
the action of natural selection, like that of individual accommodation,
will not bring it about. By either method only that is preserved which
is useful.

There is likewise clearly an opportunity for natural selection to pro-
duce a race showing increased precision and adaptiveness in the move-
ments brought about by stimulation. As we have seen on page 305, the
reactions of Paramecium to heat are so much more effective than those
of Bursaria that if locally heated regions were part of the usual environ-

ment of the two organisms, the Bursarie would, for the greater part,
¥

322 BEHAVIOR OF THE LOWER ORGANISMS

soon be killed, while the Paramecia would not suffer. The latter would,
therefore, be selected, as compared with the former. But there exist
variations of reaction even among individuals of the same species.
Some specimens of Bursaria when stimulated by heat show a greater
inclination to swim freely, revolving on the long axis, than do the ma-
jority, that sink quickly to the bottom and cease to revolve. The former
are saved from the heat, while the latter are killed. In time there might
thus be developed a race of Bursariz that were as well protected by their
behavior from the action of heat as are Paramecia.

What are the characteristics that would be preserved by natural
selection? First it seems clear that under usual conditions the regula-
tive power would tend to be preserved. So long as the environment is
a changing one, those individuals that can alter their behavior to fit the
new conditions would live, while any that cannot do so will be killed,
so that any variation in the direction of less regulative power will be cut
off. But under quite uniform conditions there might be no advantage
in this regulative power, and no selection based upon it.

Second, those variations will be preserved that are in line with the
general tendency of the behavior. In other words, those variations will
persist that tend in the same direction as the adaptation of the individuals,
due to selection of overproduced movements and the law of the resolu-
tion of physiological states. This will be made clear by an illustration.

Most ciliate infusoria may swim freely through the water, may creep
along surfaces, may exude mucus to form a cyst, and may burrow about
in the.débris at the bottom of the water. Some show one habit in a more
marked way, others another. Let us suppose a ciliate infusorian with a
cylindrical body covered uniformly with cilia, that may behave in all
these ways. It responds to stimulation by trial of the different reactions
which it has at command, continuing, in accordance with the principle
of the resolution of physiological states, that reaction which proves
successful. Suppose that a number of the individuals come thus to
react habitually in the first of the four ways mentioned above, others in
the second, others in the third, and still others in the fourth. All these
different methods have advantages for meeting unfavorable conditions,
and all are found as a prevailing reaction in different ciliates.

We have then four groups of ciliate organisms, all alike structurally,
but with different habits. How will natural selection act on these?

(1) In the first group, that swim freely through the water, like Para-
mecium, all variations that favor quickness of reaction, rapidity of move-
ment, and precision of diréction will be advantageous, and the indi-
viduals possessing them will tend to be selected. Specimens with body
ill-shaped for rapid movement, with cilia weak or unequally distributed,

DEVELOPMENT OF BEHAVIOR 323

or with awkward methods of moving, will be killed by their inability
to escape with sufficient rapidity from powerful agents. There will
thus be a tendency to develop a fishlike form, adapted for rapid move-
ments through the water; close-set, uniform cilia, and a tendency to
revolve on the long axis; in other words, such characteristics as we find
in Paramecium. :

(2) In the second group, which reacts, like Oxytricha, by running
along the bottom, variations of an entirely different character will be
advantageous. The original cylindrical form can bring but few of its
cilia against a surface, and presents much resistance to the water. Varia-
tions in the direction of a flat form, bringing many cilia against the
surface, and presenting little resistance to the water as it runs along,
will be advantageous, and individuals with such variations will be se-
lected. The cilia on the surface kept against the bottom will be the all-
important ones, so variations in the direction of increased size, strength,
and rapidity of these cilia will be preserved; they will develop into
“cirri” and other leglike structures. The cilia on the upper side of
the body will be not merely useless, but a hindrance; hence they will
tend to be lost. The tendency to revolve on the long axis will be in-
jurious and will likewise tend to disappear by selection of those that
do not thus revolve. In this way, under the action of natural selection,
an organism will be developed having totally different characteristics
from the organisms of the first set, that react by swimming freely. It
will naturally approach the characteristics shown by Stylonychia, rather
than those of Paramecium.

(3) On the third organism, which reacts to intense agents by secret-
ing a layer of mucus about itself, natural selection will act in a still
different manner. There will be no tendency to select rapidly moving
individuals, nor those having larger or more numerous cilia, nor those
having cilia distributed in any Special way; all these characteristics
will indeed be disadvantageous. Spiral swimming will not be developed.
Those organisms that produce a thicker layer of mucus, of a more re-
sistant character, and do this the more rapidly, will be selected.

(4) The fourth organism, which habitually reacts by burrowing
into the detritus at the bottom of the water, will be acted upon by natu-
ral selection in a still different way. Only those characteristics which
aid the burrowing will be useful and therefore selected. There will
be no tendency to produce a swiftly swimming organism, nor one adapted
to running along the bottom, nor one secreting a thick and resistant
layer of mucus.

To sum up, it appears that only those variations are of advantage
that are used, and only such variations can be preserved by the action

324 BEHAVIOR OF THE LOWER ORGANISMS

of natural selection. Only such characteristics can be selected as are
in line with the efforts of the organism. A variation which might be of
inestimable advantage to an organism that reacts by swimming would
be entirely lost on one that burrows in the earth. The organism deter-
mines by its own actions the direction of its development under the
action of natural selection. When it adopts a certain line of behavior,
it decides to a large degree the future career of the race. Development
through the action of natural selection must then follow as definite a
trend as does the behavior of the individual and indeed the same trend,
for it is guided by this behavior. Individual selection guides natural
selection.

Individual selection, with its production of definite adaptive reac-
tions, is due, of course, to selection from varied movements, later fixed
by the law of the readier resolution of physiological states." With this
in mind, we may express what we have just brought out as follows: In-
dividual selection (intelligence) and natural selection are merely different
methods of selecting adaptive ways of reacting. The former selects
the adaptive response from among diverse reactions of the same indi-
vidual; while natural selection selects the adaptive response from among
diverse reactions of different individuals.

This may be illustrated as follows: Let us suppose an organism
whose action system includes the different acts 1, 2, 3, 4, 5, 6, 7, 8, 9.
When the physiological processes of this animal are interfered with by
external agents, it tends to run through these nine reactions, in the order
given above — as Stentor runs through its four or five reactions. Sup-
pose that under a certain frequently recurring injurious condition the
reaction 7 is the adaptive one, relieving the interference with the physio-
logical processes. The organism runs through the series to 7, then stops
(since the cause for further reaction has ceased). It now retains this
reaction as the immediate response to the given condition, through the
law of the readier resolution of physiological states. Many of the indi-
viduals are killed before 7 is reached, but after this adaptive reaction has
become fixed, no others are killed. The young of these individuals
must, however, begin at the beginning of the series, so that many will
be destroyed.

Let us suppose that in another group there are, among many different
individuals, congenital variations in the order in which the nine re-
sponses are given. Some respond by the series 2, 3, 7, 1, 4, 5, 6, 8, 9.
These reach the adaptive reaction 7 sooner than do those following the
usual order, hence fewer are killed by the injurious condition. Others
react in the order 7, 4, 3, 5, 1, 2, 6, 8,9. The first reaction is here the

* This is the process known as intelligence, in higher animals. See Chapter XX.

DEVELOPMENT OF BEHAVIOR 325

adaptive one. Hence the series goes no farther (since the cause for
reaction ceases at once), and these organisms are not killed at all by the
injurious condition. They are thus selected, as compared with those
reacting in the usual way, and their method of reacting, being congenital,
is inherited by posterity. In the course of time all the remaining indi-
viduals of this group will respond at once, like those of the previous
group, by the reaction 7.

Thus individual selection and natural selection necessarily work to
the same result. One selects from among the different acts of the same
individual, the other from among those of different individuals. The thing
selected is the same in each case, — namely, the adaptive reaction.

If there exist at the same time the power of individual modification
and the variations on which natural selection acts, then under uniform
conditions the latter will be more effective, since it results in immediate
response by the adaptive reaction, while the former requires that every
new individual should go through the trial series, with its attendant
dangers of destruction. If the conditions are very severe, in time only
the individuals which have inherited the immediate adaptive response
will survive. Thus, through the action of natural selection these or-
ganisms will have an inborn tendency to react directly in an adaptive
way, whereas in previous generations most of the individuals of the race
acted in this manner only as a result of individual modification through
experience.

Furthermore, it may be pointed out that in the course of time an
organism which had adopted some special type of behavior, as burrow-
ing, would become quite unadapted to other behavior, as running along
the bottom or swimming through the water. It develops structures,
under the influence of its adaptive behavior, that make it difficult or
perhaps impossible for the organism to react in any other way than by
burrowing. After a time, then, it will lose all tendency to react in other
ways, because it cannot react in other ways, owing to the structural
changes it has undergone. In most cases the specialization will not go
so far as this, and the organism will retain the power of attempting other
methods of reaction; that is, of performing other movements. But
these movements will be ineffectual, because the structures of the or-
ganism are not adapted to their performance. They will therefore
not relieve the organism from stimuli; hence they will be quickly
exchanged for the movements which are effective. Thereafter the or-
ganism will always react by these movements on which its structure is
based. If these first few ineffectual movements are not observed, it
will appear that the organism has been rigidly limited from the beginning
to this one type of behavior. Apparently there exist few if any organisms

- 326 BEHAVIOR OF THE LOWER ORGANISMS

which do not show, in their younger stages at least, a few such ineffectual
movements,

Baldwin suggests that the same process may go farther than this,
in the following way: After the development, under the influence of
a certain reaction method, of structures fitted to carry out that method,
another congenital variation may occur, by which energy will be dis-
charged directly into this apparatus, in the way necessary for perform-
ing the accustomed reaction, without any previous trial. It is urged that
after the apparatus has been developed, the further variation required
would probably be slight and not unlikely to occur. The organisms
having this variation must react more readily and rapidly than those in
which a trial is required, hence they might be selected. Thus in time
in the entire race the reaction would be limited to this particular method.
There seems to be no theoretical difficulty as to the occurrence of such
a variation; if it occurs, development would doubtless take place in the
way set forth, provided the environment remain sufficiently constant.
But perhaps there would be little difference in reality between the be-
havior of such an organism, and one which had merely developed such
structures as to make difficult any kind of reaction save one. The latter
would still reserve the capability of developing other reactions, under
changed circumstances, while the former would not.

The guidance of natural selection by the actions of the individuals
that we have illustrated above, is what has been called “organic selec-
tion.” The latter is evidently merely an exposition of how natural
selection acts, not anything additional to natural selection, or differing
from it in principle. For a general discussion of the questions which
it involves, reference should be made to J. Mark Baldwin’s “ Develop-
ment and Evolution.”

Is natural selection, thus guided by individual accommodation, suf-
ficient to account for the progress of the race in behavior? It is clear
that natural selection cannot account for the origin of anything; only
that can be selected’ which already exists. All the potency of behavior
and of everything else that exists must lie in the laws of matter and
energy, — physical and chemical, and possibly vital laws. Whatever
the part assigned to natural selection, the superlative importance of
these laws remains; they must continue the chief field for scientific inves-
tigation. All that natural selection is called upon to explain is the fact
that at a given time such and such particular manifestations of these
general laws exist, rather than certain other manifestations. In the field
of behavior it is called to explain only the fact that this particular organ-
ism now behaves in this particular way, rather than in some other one
of the infinite number of possible ways. Can it explain this?

DEVELOPMENT OF BEHAVIOR 327

The fact is established that organisms which vary in such a way as
to make them unfitted to carry out the functions which they undertake
are destroyed. The correlative fact that organisms which vary in such
a way as to perform their functions better than the average are not so
usually destroyed, is likewise established. The further fact is established
that such congenital variations occur and are often handed on to the off-
spring. These three facts show that natural selection is beyond ques-
tion a factor in the development of behavior. The only question is as
to the extent of its agency. This depends on the number and extent
of the congenital variations that occur. If these are sufficiently numer-
ous and sufficiently varied, then it seems clear that natural selection
guided by individual accommodation, would produce the results which we
see. Its method of action is exactly what is needed to produce the ob-
served results; the only question is whether the material presented to
it in congenital variations is sufficient. The answer to this question
must come, if it ever comes, from that study of variations which has
received such an impulse in recent years. The recent studies of De
Vries in mutation seem especially promising from this point of view. If
it should appear that the material presented by congenital variations is
not sufficient to account for the observed development, we should be
forced apparently to turn once more to the possibility of the inheritance
of the characteristics developed during the lifetime of the organism.
The question of the inheritance of acquired characters cannot as yet be |
considered finally settled.

The view that the development of behavior is based largely on selec-
tion from among varied movements, with subsequent retention of the
selected movements, to which we have come through a study of the be-
havior of the lower organisms, is of course not a new one. A theory
to this effect has been set forth by Spencer and Bain, and has been
especially developed in recent years by J. Mark Baldwin. The obser-
vations set forth in the present work lead to views differing in some
important respects from these developed by Baldwin and Bain, par-
ticularly as to the nature of the causes which produce the varied move-
ments. Space will not permit our entering here into a discussion of
these differences. The reader may be referred for a discussion of some
of the general bearings of this theory to the two volumes of Baldwin
(1897, 1902). Possibly the most lucid statement of this theory, in its
general bearings, is that recently given by Hobhouse (1901).

LITERATURE XIX

BALDWIN, 1897, 1902; HOBHOUSE, I901 ; SPENCER, 1894 (Section 236, pp. 244-
245); BAIN, 1888 (p. 315); 1894 (pp. 323, 324).

CHAPTER XX

RELATION OF BEHAVIOR IN LOWER ORGANISMS TO PSYCHIC
BEHAVIOR

In describing the behavior of lower organisms we have used in the
present work, so far as possible, objective terms — those having no im-
plication of psychic or subjective qualities. We have looked at organ-
isms as masses of matter, and have attempted to determine the laws of
their movements. In ourselves we find movements and reactions re-
sembling in some respects those of the lower organisms. We draw away
from heat and cold and injurious chemicals, just as Paramecium does.

Our behavior depends on physiological states, as does that of Stentor.

But in Ne there is the very interesting additional fact that t these
movements, reactions, and physiological states are often accompanied by
subjective ective_ states, — states _of consciousness} . Different states of con-
th cer are as varied as the different possibilities of reaction; indeed,
more varied. In speaking of behavior in ourselves, and as a rule in
higher animals, we use terms based on these subjective states, as pleas-
ure and pain, sensation, memory, fear, anger, reason, and the like.
The peculiarity of subjective states is that they can be perceived
only by the one person directly experiencing them, — by the~subject:
Each of us knows directly states of consciousness only in himself. We
cannot by observation and experiment detect such states in organisms
outside of ourselves. But observation and experiment are the only
direct means of studying behavior in the lower organisms. We can
reason concerning their behavior, and through reasoning by analogy
we may perhaps conclude that they also have conscious states. But
reasoning by analogy, when it-is afterward tested by observation and
experiment, has often shown itself fallacious, so that where it cannot
be tested, we must distrust its conclusiveness. Moreover, in different
men it leads to different conclusions, so that it does not result in ad-
mitted certainty. Hence it seems important to keep the results of obser-
vation and experiment distinct from those of reasoning by analogy, so
that we may know what is really established. On this account it is
customary among most physiologists not to use, in discussing the be-
havior of the lower organisms, psychic terms, or those implying sub-
328

RELATION TO PSYCHIC BEHAVIOR 329

jective states. This has the additional ground that the ideal of most
scientific men is to explain behavior in terms of matter and energy, so
that the introduction of psychic implications is considered superfluous.

While this exclusive use of objective terms has great advantages, it
has one possible disadvantage. It seems to make an absolute gulf be-
tween the behavior of the lower organisms on the one hand, and that of
man and higher animals on the other. From a discussion of the be-
havior of the lower organisms in objective terms, compared with a dis-
cussion of the behavior of man in subjective terms, we get the impression
of complete discontinuity between the two.

Does such a gulf actually exist, or does it lie only in our manner of
speech? We can best get evidence on this question by comparing the
objective features of behavior in lower and in higher organisms. In
any animal outside of man, and even in man outside of the self, the
existence of perception, choice, desire, memory, emotion, intelligence,
reasoning, etc., is judged from certain objective facts — certain things
which the organisms do. Do we find in the lower organisms objective
phenomena of a similar character, so that the same psychic names would
be applied to them if found in higher organisms? Do the objective
factors in the behavior of lower organisms follow laws that are similar
to the laws of psychic states? Only by comparing the objective factors
can we determine whether there is continuity or a gulf between the be-
havior of lower and higher organisms (including man), for it is only
these factors that we know.

Let us then examine some of the concepts employed in discussions
of the behavior of higher animals and man, determining whether there
exist any corresponding phenomena in lower organisms. We shall not
attempt to take into consideration the scholastic definitions of the terms
used, but shall judge of them merely from the objective phenomena on
which they are based.

When we say that an animal perceives something, or that it shows
perception of something, we base this statement on the observation that
it reacts in some way to this thing. On the same basis we could make
the statement that Amoeba perceives all classes of stimuli which we our-
selves perceive, save sound (which is, however, essentially one form of
mechanical stimulation). Perception as judged from our subjective
experiences means much more: how much of this may be present in
animals outside the self we cannot know.

Discrimination is a term based, so far as objective evidence goes,
upon the observed fact that organisms react differently to different
stimuli. In this sense Paramecium, as we have seen, discriminates
acids from alkalies; Amoeba discriminates a Euglena cyst from a grain

330 BEHAVIOR OF THE LOWER ORGANISMS

of sand, and in general all lower organisms show discrimination in many
phases of their behavior.

Choice is a term based objectively on the fact that the organism ac-
cepts or reacts positively to some things, while it rejects or reacts nega-
tively or not at all to others. In this sense all lower organisms show
choice, and at this we need not be surprised, for inorganic substances
show a similar selectiveness. The distinctive thing about the choice of
organisms is that it is regulatory; organisms on the whole choose those
things which aid their normal life processes and reject those that do not.
This is what justifies the use of the term ‘‘choice,” as contrasted with
the mere selectiveness of inorganic reactions. Choice in this regulatory
sense is shown by lower organisms, as we have seen in detail in previous
chapters. Choice is not perfect, from this point of view, in either lower
or higher organisms. Paramecium at times accepts things that are use-
less or harmful to it, but perhaps on the whole less often than does man.

The methods by which choice is shown in particular organisms have
been set forth in our descriptive chapters. We may refer particularly
to the account of choice in the infusoria, given on page 183. The free-
swimming infusoria as they move about are continually rejecting cer-
tain things and accepting others, and this choice is regulatory. Their
behavior is based throughout on the method of trial, and _ this
involves an act comparable to choice in almost every detail. Whatever
the condition met, the infusorian must either accept it by going ahead,
or reject it by backing and giving the avoiding reaction. We can al-
most say that its whole behavior is a process of choice; that choice is
the essential feature of its behavior. For the other lower organisms
that we have taken up, a consideration of details would discover
activities involving regulatory choice almost as continuously as in the
infusoria.

Is not what we call attention in higher organisms, when considered
objectively, the same phenomenon that we have called the interference
of one stimulus with the reaction to another? At the basis of attention
lies objectively the phenomenon that the organism may react to only one
stimulus even though other stimuli are present which would, if acting
alone, likewise produce a response. The organism is then said to at-
tend to the particular stimulus to which it responds. This.fundamental
phenomenon is clearly present in unicellular organisms. Stentor and
Paramecium when reacting to contact with a solid “pay no attention”’
to a degree of heat or a chemical or an electric current that would pro-
duce an immediate reaction in a free individual. On the other hand,
individuals reacting to heat or a chemical may not respond to contact
with a mass of bacteria, to which they would under other conditions

RELATION TO PSYCHIC BEHAVIOR 331

react positively. In our chapter on reaction under two or more stimuli
in the infusoria, many examples of this character are given.

Indeed, attention in this objective sense seems a logical necessity for
the behavior of any organism having at its command more than a single
action. The characteristic responses to two present stimuli may be in-
compatible with each other. The organism must then react to one or
the other, since it cannot react to both; it thus attends (objectively) to
one, and not to the other. Only in case there is no reaction at all in
the presence of two stimuli, or in case its reaction is precisely inter-
mediate between those required by the two, could the basis of attention
be considered lacking. An organism behaving in this way would be
quickly destroyed as a result of its indecisive and ineffective behavior.

In higher animals and man we distinguish certain different condi-
tions, — ‘‘states of feeling,” “‘emotions,” “appetites,” ‘‘desires,” and
the like. In all cases except the self, these various states are distin-
guished through the fact that the organism behaves differently in the
different conditions, even though the external stimuli may be the same.
We find a parallel condition of affairs in the lower organisms. Here,
as we have seen, the behavior under given external conditions depends |
largely on the physiological condition of the individual. Many illus-
trations of this fact are given in preceding chapters, so that we need not
dwell upon it here.

In the lower organisms we can even distinguish a number of states
that are parallel, so far as observation can show, with those distin-
guished and named in higher animals and man. To begin with some
of the simpler ones, the objective correlate of hunger can be distin-
guished at least as low in the scale as Hydra and the sea anemone.
These animals, as we have seen, take food only when hungry, and if
very hungry, will take substances as food which they otherwise reject.
Doubtless hunger could be detected in still lower organisms by proper
experiments. A resting condition comparable to sleep is found, as we
have seen, in the flatworm (p. 253), while there seems to be no indica-
tion of such a state in the infusoria (p. 181). Fatigue can of course be
distinguished in all living things, including separated muscles.

Correlative with hunger, there exists a state which corresponds so
far as objective evidence goes with what we should call in higher animals
a desire for food. Hydra when hungry opens its mouth widely when
immersed in a nutritive liquid. In the flatworm, we can distinguish
a certain physiological condition in which the animal moves about in
an eager, searching way, as if hunting for food. Even in Amceba we
find a pertinacity in the pursuit of food (p. 14 and Fig. 21) such as we
woul attribute in a higher animal to a desire for it.

332 BEHAVIOR OF THE LOWER ORGANISMS

All the way up the scale, from Amoeba and bacteria to man, we find
that organisms react negatively to powerful and injurious agents. In
man and higher animals such reactions are usually said to be due to
pain. In the lower organisms the objective facts are parallel, and natu-
rally lead to the assumption of a physiological state similar to what we
have in the higher forms. As to subjective accompaniments of such
a state we of course know nothing in animals other than ourselves. The
essential cause of the states corresponding to pain is interference with
any of the processes of which the organism is the seat, and the correlate
in action of these states is a change in movement. This point will
be developed in our final chapter.

A similar basis exists for distinguishing throughout the organic
series a physiological state corresponding to that accompanying pleasure
in man. This is correlated with a relief from interference with the life
processes, or with the uninterrupted progression of these processes.

In man and higher animals we often find a negative reaction to that
which is not in itself injurious, but which is usually followed by some-
thing injurious. The sight of a wild beast is not injurious, considered
by itself, but as preceding actual and injurious contact with this beast,
it leads to powerful negative reactions. Such reactions are said to be
due to fear. In fear there is then a negative reaction to a representative
stimulus — one that stands for a really injurious stimulation. In lower
organisms we find the objective indications of a parallel state of affairs.
The infusoria react negatively to solutions of chemicals that are not,
so far as we can determine, injurious, though they would naturally,
under ordinary circumstances, be immediately followed by a solution
so strong as to be injurious. Euglena reacts negatively when darkness
affects only its colorless anterior end, though we have reason to believe
that it is only the green part of the body which requires the light for the
proper discharge of its functions. A much clearer case is seen in the
sea urchin, which reacts by defensive movements when a shadow falls
upon it, though shade is favorable to its normal functions. Objectively,
fear has at its basis the fact that a negative reaction may be produced
by a stimulus which is not in itself injurious, provided it leads to an
injurious stimulation; this basis we find throughout organisms.

Sometimes higher animals and man are thrown into a “state of
fear,’ such that they react negatively to all sorts of stimuli, that under
ordinary circumstances would not cause such a reaction. A similar
condition of affairs we have seen in Stentor and the flatworm. After
repeated stimulation, they react negatively to all stimuli to which they
react at all.

The general fact of which the reactions through fear are onlya special

RELATION TO PSYCHIC BEHAVIOR 333

example is the following: Organisms react appropriately to repre-
sentative stimuli. That is, they react, not merely to stimuli that are in
themselves beneficial or injurious, but to stimuli which lead to bene-
ficial or injurious conditions. This is as true of positive as of negative
reactions. It is true of Amoeba when it moves toward a solid body that
will give it an opportunity to creep about and obtain food. It is true of
Paramecium when it settles against solids (even bits of filter paper),
because usually such solids furnish a supply of bacteria. It is true of
the colorless flagellate Chytridium and the white Hydra, when they move
toward a source of light and thus come into the region where their prey
congregate. There seems to be no general name for this positive re-
action to a representative stimulus. In man we call various subjective
aspects of it by different names, — foresight, anticipation, prudence,
hope, etc.

The fact that lower as well as higher organisms thus react to repre-
sentative stimuli is of the greatest significance. It provides the chief
condition for the advance of behavior to higher planes. At the basis
of reaction of this character lies the simple fact that a change, even though
neutral in its effect, may cause reaction (p. 294). This taken in con-
nection with the law of the resolution of physiological states (p. 291)
permits the establishment of a negative or positive reaction, as the case
may require, as a response to a given change. The way in which this
may take place we have attempted to set forth on page 316.

Related to these reactions to representative stimuli are certain other
characteristics distinguished in the behavior of man and higher animals.
The objective side of memory and what is called habit is shown when
the behavior of an organism is modified in accordance with past stimuli
received or past reactions given. If the behavior is merely changed in
a way that is not regulatory, as by fatigue, we do not call this memory.
In memory the reaction is modified in such a way that it is now more
adequate to the conditions to be met. Habit and memory in this ob-
jective sense are clearly seen in the Crustacea, and in the low accelous
flatworm Convoluta (p. 255). Something of a similar character is seen
even in the protozoan Stentor. After reacting to a weak stimulus which
does not lead to an injurious one it ceases to react when this stimulus
is repeated, while if the weak stimulus does lead to an injurious one,
the animal changes its behavior so as to react next time in a more effec-
tive way; and it repeats this more effective reaction at the next inci-
dence of the stimulus. Habit and memory, objectively considered,
are based on the law of the resolution of physiological states (p. 291),
which may be set forth in application to the present subject as follows:
If a given physiological state, induced by a stimulus, is repeatedly

334 BEHAVIOR OF THE LOWER ORGANISMS

resolved into a succeeding state, this resolution becomes easier, and may
take place spontaneously, so that the reaction induced is that due pri-
marily to the second physiological state reached. Wherever we find
this law in operation, we have the ultimate basis from which habit and
memory (objectively considered) are developed.

From memory in the general sense it is customary to distinguish
associative memory. ‘This is characterized objectively by the fact that
the response at first given to one stimulus comes, after a time, to be
transferred to another one. Examples of associative memory are seen
in the experiments of Yerkes and Spaulding on crustaceans, described
in Chapter XII. It may be pointed out that the essential basis for
associative memory is the same law of the resolution of physiological
states which we have set forth in the last paragraph as underlying ordi-
nary memory. The physiological condition induced by the first stimu-
lus (sight of the screen, in Spaulding’s experiments) is regularly re-
solved into that due to the second stimulus (food, in the experiments
just mentioned). After a time the resolution becomes spontaneous, so
that the physiological state primarily due to the food is reached imme-
diately after the introduction of the screen, even though no food is given.
There seems to be no difference in kind, therefore, between associative
memory and other sorts; they are based on the same fundamental law.
The existence of associative memory has often been considered a criterion
of the existence of consciousness, but it is clear that the process under-
lying it is as readily conceivable in terms of matter and energy as are other
physiological processes. Even in inorganic colloids, as we have seen
(p. 317), the properties depend on the past history of the colloid, and the
way in which it has reached the condition in which it is now found. If
this is conceivable in terms of matter and energy, it is difficult to see why
the law of the readier resolution of physiological states is not equally so.

Intelligence is commonly held to consist essentially in the modifica-
tion of behavior in accordance with experience. If an organism reacts
in a certain way under certain conditions, and continues this reaction
no matter how disastrous the effects, we say that its behavior is unin-
telligent. If on the other hand it modifies its behavior in such a way as
to make it more adequate, we consider the behavior as in so far intel-
ligent. It is the ‘‘correlation of experiences and actions’’ that consti-
tutes, as Hobhouse (1go1) has put it, “the precise work of intelligence.”

_It appears clear that we find the beginnings of such adaptive changes
of behavior even in the Protozoa. They are brought about through the
law in accordance with which the resolution of one physiological state
into another takes place more readily after repetition, — in connection
with the other principle that interference with the life processes causes

RELATION TO PSYCHIC BEHAVIOR 335

a change of behavior. These laws apparently form the fundamental
basis of intelligent action. This fundamental basis then clearly exists
even in the Protozoa; it is apparently coextensive with life. It is diffi-
cult if not impossible to draw a line separating the regulatory behavior
of lower organisms from the so-called intelligent behavior of higher
ones; the one grades insensibly into the other. From the lowest organ-
isms up to man behavior is essentially regulatory in character, and what
we call intelligence in higher animals is a direct outgrowth of the same
laws that give behavior its regulatory character in the Protozoa.
Thus-it seems possible to trace back to the lowest organisms some of
the phenomena which we know, from objective evidence, to exist in the
behavior of man and the higher animals, and which have received special
names. It would doubtless be possible to extend this to many other
phenomena. Many conditions which we can clearly distinguish in
man must be followed back to a single common condition in the lower
organism. But this is what we should expect. Differentiation takes
place as we pass upward in the scale in these matters as in others.
Because we can trace these phenomena back to conditions found in
unicellular forms, it does not follow that the behavior of these organisms
has as many factors and is as complex as that of higher animals.
The facts are precisely parallel with what we find to be true for other
functions. Amoeba shows respiration, and all the essential features of
respiration in man can be traced back to the condition in such an organ-
ism. Yet in man respiration is an enormously complex operation,
while in Ameeba it is of the simplest character possible — apparently
little more than a mere interdiffusion of gases. In the case of behavior
there is the same possibility of tracing all essential features back to the
lower organisms, with the same great simplification as we go back.

THE QUESTION OF CONSCIOUSNESS

All that we have said thus far in the present chapter is independent
of the question whether there exist in the lower organisms such subjec-
tive accompaniments of behavior as we find in ourselves, and which
we call consciousness. We have asked merely whether there exist in
the lower organisms objective phenomena of a character similar to what
we find in the behavior of man. To this question we have been com-
pelled to.give an affirmative answer. So far as objective evidence goes,
there is no. difference in kind, but a complete continuity between the
behavior of lower and of higher organisms.

Has this any bearing on the question of the existence of conscious-
ness in lower animals? It is clear that objective evidence cannot give

336 BEHAVIOR OF THE LOWER ORGANISMS

a demonstration either of the existence or of the non-existence of con-
sciousness, for consciousness is precisely that which cannot be perceived
objectively. No statement concerning consciousness in animals is open
to verification or refutation by observation and experiment. There
are no processes in the behavior of organisms that are not as readily
conceivable without supposing them to be accompanied by conscious-
ness as with it.

But the question is sometimes proposed: Is the behavior of lower
organisms of the character which we should “naturally” expect and
appreciate if they did have conscious states, of undifferentiated character,
and acted under similar conscious states in a parallel way to man? Or
is their behavior of such a character that it does not suggest to the
observer the existence of consciousness ?

If one thinks these questions through for such an organism as Para-
mecium, with all its limitations of sensitiveness and movement, it appears
to the writer that an affirmative answer must be given to the first of the
above questions, and a negative one to the second. Suppose that this
animal were conscious to such an extent as its limitations seem to permit.
Suppose that it could feel a certain degree of pain when injured; that
it received certain sensations from alkali, others from acids, others from
solid bodies, etc., — would it not be natural for it to act as it does?
That is, can we not, through our consciousness, appreciate its drawing
away from things that hurt it, its trial of the environment when the
conditions are bad, its attempting to move forward in various directions,
till it finds one where the conditions are not bad, and the like? To
the writer it seems that we can; that Paramecium in this behavior
makes such an impression that one involuntarily recognizes it as a little
subject acting in ways analogous to our own. Still stronger, perhaps,
is this impression when observing an Amceba obtaining food as shown
in Figs. 19 and 21. The writer is thoroughly convinced, after long study
of the behavior of this organism, that if Amoeba were a large animal, so
as to come within the everyday experience of human _ beings, its be-
havior would at once call forth the attribution to it of states of pleasure
and pain, of hunger, desire, and the like, on precisely the same basis
as we attribute these things to the dog. This natural recognition is
exactly what Miinsterberg (1900) has emphasized as the test of a
subject. In conducting objective investigations we train ourselves to
suppress this impression, but thorough investigation tends to restore it
stronger than at first.

Of a character somewhat similar to that last mentioned is another
test that has been proposed as a basis for deciding as to the conscious-
ness of animals. This is the satisfactoriness or usefulness of the concept

RELATION TO PSYCHIC BEHAVIOR 337

of consciousness in the given case. We do not usually attribute con-
sciousness to a stone, because this would not assist us in understanding
or controlling the behavior of the stone. Practically indeed it would
lead us much astray in dealing with such an object. On the other
hand, we usually do attribute consciousness to the dog, because this is use-
ful; it enables us practically to appreciate, foresee, and control its actions
much more readily than we could otherwise do so. If Amoeba were
so large as to come within our everyday ken, I believe it beyond ques-
tion that we should find similar attribution to it of certain states of con-
sciousness a practical assistance in foreseeing and controlling its behavior.
Ameeba is a beast of prey, and gives the impression of being controlled
by the same elemental impulses as higher beasts of prey. If it were as
large as a whale, it is quite conceivable that occasions might arise when
the attribution to it of the elemental states of consciousness might save
the unsophisticated human being from the destruction that would result
from the lack of such attribution. In sucha case, then, the attribution
of consciousness would be satisfactory and useful. In a small way this
is still true for the investigator who wishes to appreciate and predict
the behavior of Amceba under his microscope.

But such impressions and suggestions of course do not demonstrate
the existence of consciousness in lower organisms. Any belief on this
matter can be held without conflict with the objective facts. All that
experiment and observation can do is to show us whether the behavior
of lower organisms is objectively similar to the behavior that in man is
accompanied by consciousness. If this question is answered in the
affirmative, as the facts seem to require, and if we further hold, as is
commonly held, that man and the lower organisms are subdivisions of
the same substance, then it may perhaps be said that objective investi-
gation is as favorable to the view of the general distribution of conscious-
ness throughout animals as it could well be. But the problem as to the
actual existence of consciousness outside of the self is an indeterminate
one; no increase of objective knowledge can ever solve it. Opinions
on this subject must then be largely dominated by general philosophical
considerations, drawn from other fields.

LITERATURE XX

CONSCIOUSNESS IN LOWER ANIMALS

CLAPAREDE, I90I, 1905; TITCHENER, 1902; MINOT, 1902; MUNSTERBERG,
1900; VERWORN, 1889; BETHE, 1898; YERKES, 1905, 1905 @; JORDAN, 1905;
v. UEXKULL, 1900 4, 1902; WASMANN, I901, 1905; LUKAS, 1905.

CHAPTER XXI
BEHAVIOR AS REGULATION, AND REGULATION IN OTHER FIELDS

1. INTRODUCTORY

EVERYWHERE in the study of life processes we meet the puzzle of
regulation. Organisms do those things that advance their welfare. If
the environment changes, the organism changes to meet the new condi-
tions. If the mammal is heated from without, it cools from within; if
it is cooled from without, it heats from within, maintaining the tempera-
ture that is to its advantage. The dog which is fed a starchy diet pro-
duces digestive juices rich in enzymes that digest starch; while under a
diet of meat it produces juices rich in proteid-digesting substances.
When a poison is injected into a mouse, the mouse produces substances
which neutralize this poison. If a part of the organism is injured, a
rearrangement of material follows till the injury is repaired. If a part
is removed, it is restored, or the wound is at least closed up and healed,
so that the life processes may continue without disturbance. Regulation
constitutes perhaps the greatest problem of life. How can the organism
thus provide for its own needs? To put the question in the popular
form, How does it know what to do when a difficulty arises? It seems
to work toward a definite purpose. In other words, the final result of
its action seems to be present in some way at the beginning, determin-
ing what the action shall be. In this the action of living things appears
to contrast with that of things inorganic. It is regulation of this charac-
ter that has given rise to theories of vitalism. The principles control-
ling the life processes are held by these theories to be of a character
essentially different from anything found in the inorganic world. This

view has found recent expression in the works of Driesch (1901, 1903).

2. REGULATION IN BEHAVIOR

Nowhere is regulation more striking than in behavior. Indeed, the
processes in this field have long served as the prototype for regulatory
action. The organism moves and reacts in ways that are advantageous
to it. If it gets into hot water, it takes measures to get out again, and

338

REGULATION IN BEHAVIOR 339

the same is true if it gets into excessively cold water. If it enters an
injurious chemical solution, it at once changes its behavior and escapes.
If it lacks material for its metabolic processes, it sets in operation move-
ments which secure such material. If it lacks oxygen for respiration,
it moves to a region where oxygen is found. [If it is injured, it flees to
safer regions. In innumerable details it does those things that are good
for it. It is plain that behavior depends largely on the needs of the
organism, and is of such a nature as to satisfy these needs. In other
words, it is regulatory.

Behavior is merely a collective name for the most obvious and most
easily studied of the processes of the organism, and it is clear that these
processes are closely connected with, and are indeed outgrowths from,
the more recondite internal processes. ‘There is no reason for supposing
them to follow laws different from those of the other life processes, or
for holding that regulation in behavior is of a different character from
that found elsewhere. But nowhere else is it possible to perceive so
clearly how regulation occurs. In the behavior of the lowest organisms
we can see not only what the animal does, but precisely how this happens
to be regulatory. The method of regulation lies open before us. This
method is of such a character as to suggest the possibility of its general
applicability to life processes. In the present chapter we shall attempt
to sum up the essential points in regulation as shown in behavior, and
to make some suggestions as to its possible application to other fields.

A. Factors in Regulation in the Behavior of Lower Organisms

In the lower organisms, where we can see just how regulation occurs,
the process is as follows: Anything injurious to the organism causes
changes in its behavior. These changes subject the organism to new
conditions. As long as the injurious condition continues, the changes
of behavior continue. The first change of behavior may not be regu-
latory, nor the second, nor the third, nor the tenth. But if the changes
continue, subjecting the organism successively to all possible different
conditions, a condition will finally be reached that relieves the organism
from the injurious action, provided such a condition exists. ‘Thereupon
the changes in behavior cease, and the organism remains in the favor-
able condition. The movements of the organism when stimulated are
such as to subject it to various conditions, one of which is selected.

This method of regulation is found in its purest form in unicellular
organisms. But, as we have seen in preceding pages, it occurs also in
higher organisms, and indeed is found in a less primitive form through-
out the animal series, up to and including man. It is commonly spoken

340 BEHAVIOR OF THE LOWER ORGANISMS

of as behavior by “trial and error.” In connection with this method of
behavior, three questions arise, which are fundamental for the theory
of regulation. The first is as follows: How is it determined what shall
cause the changes in behavior resulting in new conditions? Why does
the organism change its behavior under certain conditions, not under
others? Second, how does it happen that such movements are pro-
duced as result in more favorable conditions? Third, how is the more
favorable condition selected? What it this selection and what does it
imply?

Our first and third questions may indeed be condensed into one,
which involves the essence of regulation. Why does the organism
choose certain conditions and reject others? This selection of the fa-
vorable conditions and rejection of the unfavorable ones presented by
the movements is perhaps the fundamental point in regulation.

It is often maintained that this selection is precisely personal or con-
scious choice, and that the behavior cannot be explained without this
factor. Personal choice it evidently is, and in man it is often conscious
choice; whether it is conscious in other animals we do not know. But
in any case this does not remove it from the necessity for analysis.
Whether conscious or unconscious, choice must be determined in some
way, and it is the province of science to inquire as to how this determina-
tion occurs. To say that rejection is due to pain, acceptance to pleasure
or to other conscious states, does not help us, for we are then forced to
inquire why pain occurs under certain circumstances, pleasure under
others. Surely this is not a mere haphazard matter. There must be
some difference in the conditions to induce these differences in the con-
scious states (if they exist), and at the same time to determine the
differences in behavior. We are therefore thrown back upon the objec-
tive processes occurring. Why are certain conditions accepted, others
rejected ?

Let us examine one or two of the simplest cases of such regulatory
selection. The green infusorian Paramecium bursaria requires oxygen
for its metabolic processes. While swimming about it comes to a region
where oxygen is lacking. Thereupon it changes its behavior, turns away,
and goes in some other direction. The white Paramecium caudatum
does the same, and so also do many bacteria; they likewise require oxy-
gen for their metabolic processes. All reject a region without oxygen.
The green Paramecium bursaria comes to a dark region. The water
contains plenty of oxygen, hence the metabolic processes are proceeding
uninterruptedly, and passing into darkness does not interfere with them.
The animal does not change its behavior, but enters the dark region
without hesitation. Later the oxygen in the water has become nearly

REGULATION IN BEHAVIOR 341

exhausted. The animal is again swimming about in the light, and the
green chlorophyll bodies which it contains are producing a little oxygen
which the infusorian uses in its metabolic processes. Now it comes
again to a dark region. In the darkness the production of oxygen by
the green bodies ceases; they no longer supply the metabolic processes
with this necessary factor. Now we find that the infusorian rejects the
darkness and turns in another direction. The white Paramecium cau-
datum does not do this, nor do the colorless bacteria. Possessing no
chlorophyll, they receive no more oxygen in the light than in the
darkness, and they pass into darkness as readily as into light. But
many colored bacteria do reject the darkness. They require light in
certain other metabolic processes, —in their assimilation of inorganic
compounds, — and when they come to the boundary between light and
darkness, they return into the light. Most bacteria reject regions con-
taining no oxygen, as we have seen. But in certain bacteria, oxygen is
not required for the metabolic processes; on the contrary, it impedes
them. These bacteria reject regions containing oxygen, swimming back
into the light. In some cases among unicellular organisms the relation
of behavior to the metabolic processes is exceedingly precise. Thus,
Engelmann (1882 a) proved that in Bacterium (or Chromatium) photo-
metricum the ultra-red and the yellow-orange rays are those most favor-
able to the metabolic processes (assimilation of carbon dioxide, etc.).
When a microspectrum is thrown on these bacteria, they are found to
react in such a way as to collect in precisely the ultra-red and the yellow-
orange. ‘The reaction consists in a change of behavior, — a reversal of
movement, — at the moment of passing from the ultra-red or the yel-
low-orange to any other part of the spectrum. At that same instant
the metabolic processes of course suffer interference. Bacteria are not
in nature subjected to pure spectral colors in bands, so that there has
been no opportunity for the production of this correspondence between
behavior and favorable conditions, through the natural selection of vary-
ing individuals.

In all these cases the behavior depends upon the metabolic processes,
. and is of such a character as to favor them. Throughout the present
volume we have found similar relations to hold for all sorts of organisms.
We find even that when the metabolic processes of a given individual
change, the behavior changes in a corresponding way.

Why does the bacterium or infusorian change its behavior and shrink
back from the darkness or the region containing no oxgyen? As a mat-
ter of fact, it needs the light or the oxygen in its metabolic processes,
and it does not shrink back from their absence unless it does need them.
But we have no reason to attribute to the bacterium anything like a

342 BEHAVIOR OF THE LOWER ORGANISMS

knowledge or idea of that relation. We do not need any purpose or
idea in the mind of the organism, or any “psychoid”’ or entelechy, to
account for the change of behavior, for an adequate objective cause
exists. We know experimentally that the darkness or the lack of oxygen
interferes with the metabolic processes. This very interference is then
evidently the cause of the change of behavior. The organism is known
to be the seat of varied processes, proceeding with a certain energy.
When there is interference with these processes, the energy overflows
into other channels, resulting in changes in behavior. This statement
is a formulation of the facts determined by observation and experiment
in the most diverse organisms. It is illustrated on almost every page
of the present work.

In the lower organisms the processes of metabolism are the chief
ones occurring, and behavior is largely determined with reference to
them. In higher organisms these usually retain their commanding réle,
but an immense number of coérdinated and subsidiary processes also
occur, and changes in behavior may be induced by interference with any
of these.

The answer to our first question is then as follows: The organism
changes its behavior as a result of interference or disturbance in its
physiological processes.

Our second question was: How does it happen that such movements
are produced as bring about more favorable conditions? This question
we have already answered, so far as lower organisms are concerned, in
our general statement on page 339. The organism does not go straight
for a final end. It merely acts,—#$in all sorts of ways possible to it, —
resulting in repeated changes of the environmental conditions. The
fundamental fact must be remembered that the life processes depend
upon internal and external conditions, and are favored by conditions
that are rather generally distributed throughout the environment of or-
ganisms. If there were no favorable conditions attainable, of course no
change of behavior could attain them. But the favorable conditions
actually exist, and if the changes of behavior continue, subjecting the
organism to all possible different conditions, a condition will finally be
reached that is favorable to the life processes. Often only a slight change
of behavior is required in order to bring about favorable conditions. If
an organism swims suddenly into a heated area, almost any change in
the direction of movement is likely to restore the conditions previously
existing. Adjustment, then, is reached by repeated changes of move-
ment.

Our third question was: How does the organism select the more
favorable condition thus reached? This question now answers itself.

.

REGULATION IN BEHAVIOR 343

It was the interference with the physiological processes that caused the
changes in behavior. As soon therefore as this interference ceases, there
is no further cause for change. The organism selects and retains the
favorable condition reached, merely by ceasing to change its behavior
when interference ceases.

Thus in the lowest organisms we find regulation occurring on the
basis of the three following facts : —

1. Definite internal processes are occurring in organisms. ~

2. Interference with these processes causes a change of behavior and
varied movements, subjecting the organism to many different conditions.

3. One of these conditions relieves the interference with the internal
processes, so that the changes in behavior cease.

It is clear that regulation taking place in this way does not require
that the end or purpose of the action shall function in any way as part
of its cause, as is held in various vitalistic theories. There is no evi-
dence that a final aim is guiding the organism. None of the factors
above mentioned appear to include anything differing in essential prin-
ciple from such methods of action as we find in the inorganic world.

Now an additional factor enters the problem. By the process which
we have just considered, the organism reaches in time a movement that
brings relief from the interfering conditions. This relieving response
becomes fixed through the operation of the law of the readier resolu-
tion of physiological states as a result of repetition (Chapter XVI, Sec-
tion 10). After reaching the relieving response a number of times by a
repeated succession of movements, a recurrence of the interfering con-
dition induces more quickly the relieving response, and in time this
becomes the immediate reaction to this interfering condition.

It is in this second stage of the process, when the relieving response
has become set through the law of the readier resolution of physiological
states by repetition, that an end or purpose seems to dominate the be-
havior. This end or purpose of course actually exists, as a subjective
state called an idea,in man. Whether any such subjective state exists
in the lower organism that has gone through the process just sketched,
of course we do not know. But some objective phenomenon, as a tran-
sient physiological state, would seem to be required in the lower animal,
corresponding to the objective physiological accompaniment of the idea
inman. The behavior in this stage is that which, in its higher reaches
at least, has been called intelligent.

But so far as the objective occurrences are concerned, there would
seem to be nothing in this later stage of the behavior involving any-
thing different in essential principle from what we find in the inorganic
world. The only additional factor is the law of the readier resolution of

344 BEHAVIOR OF THE LOWER ORGANISMS

physiological states after repetition. While possibly our statement of this
law may not be entirely adequate, there would seem to be nothing im-
plied by it that is specifically vital, in the sense that it differs in essential
principle from the methods of action seen in the inorganic world. This
law of the readier resolution of physiological states after repetition pre-
sents indeed many analogies with various chains of physical and chemi-
cal action.’ It certainly by no means requires in itself the action of any
‘final cause,’’ — that is, of an entity that is at the same time purpose
and cause. On the other hand, it undoubtedly does produce that type
of behavior which has given rise to the conception of the purpose acting
as cause. This conception is in itself of course a correct one, so far as
we mean by a purpose an actual physiological state of the organism,
determining behavior in the same manner as other factors determine it.
But such a physiological state (subjectively a purpose) is a result of a
foregoing objective cause, and acts to produce an effect in the same way
as any other link in the causal chain. It would seem therefore to pre-
sent no basis for theories of vitalism, so far as these depend on anything
like the action of final causes.

That regulation takes place in the behavior of many animals in the
manner above sketched may be affirmed as a clearly established fact,
and it seems to be perhaps the only intelligible way in which regulatory
behavior could be developed in a given individual.

But we are, of course, confronted by the fact that many individuals
are provided at birth with definite regulatory methods of reaction to cer-
tain stimuli. In these cases the animal is not compelled to go through
the process of performing varied movements, with subsequent fixation of
the successful movement. How are such cases to be accounted for?

If the regulatory method of reaction acquired through the process
sketched in the preceding paragraphs could be inherited, there would of
course be no difficulty in accounting for such congenital regulatory re-
actions. In Protozoa this is apparently the real state of the case; there
appears to be no reason why the products of reproduction by division
should not inherit the properties of the individual that divides, however
these properties were attained. But in the Metazoa such inheritance of
acquirements presents great theoretical difficulties, and has not been ex-
perimentally demonstrated to occur, though it is perhaps too early to con-
sider the matter as yet out of court. If such inheritance does not occur,
the existence of congenital definite regulatory reactions would seem
explicable only on the basis of the natural selection of individuals having
varying methods of reaction, unless we are to adopt the theories of vital-
ism. In the method we have sketched above, a certain reaction that is

1 See note, page 317.

REGULATION IN BEHAVIOR 345

regulatory is selected, through the operation of physiological laws, from
among many performed by the same individual. In natural selection
the same reaction is selected from among many performed by different
individuals —in both cases because it is regulatory — because it
assists the life processes of the organism. The two factors must then
work together and produce similar results.’ In both, the essential point
is a selection from among varied activities.

We must here notice the fact that we often find in organisms be-
havior that is not regulatory. How are we to account for this? With-
out going into details, it is clear that there are a number of factors that
would produce this result. First, interference with the life processes is
not the only cause of reaction. The organism is composed of matter
that is subject to the usual laws of physics and chemistry. External
agents may of course act on this matter directly, causing changes in
movement that are not regulatory. Second, the organism can perform
only those movements which its structure permits. Often none of these
movements can produce conditions that relieve the existing interference
with the life processes. Then the organism can only try them, without
regulatory results, and die (see, for example, such a case in the flatworm,
p- 244). Further, certain responses may have become fixed, in the way
described above, because under usual conditions they produce adjust-
ment. Now if the conditions change, the organism still responds by
the fixed reaction, and this may no longer be regulatory. The organ-
ism may then be destroyed before a new regulatory reaction can
be developed by selection from varied movements. This condition of
affairs is of course often observed.

All together, the regulatory character of behavior as found in many
animals seems intelligible in a perfectly natural, directly causal way, on
the basis of the principles brought out above. We may summarize these
principles as (1) the selection through varied movements of conditions
not interfering with the physiological processes of the organism (“trial
and error’’); (2) the fixation of the adaptive movements through the
law of the readier resolution of physiological states after repetition.

3. REGULATION IN OTHER FIELDS

Is it possible that individual regulation in other fields is based on
the same principles that we have set forth above for behavior? Bodily
movement is only one of the many activities that vary, and variations
of any of the organic activities may impede or assist the physiological

For a discussion of the relation of these two factors, see Chapter XIX.

346 BEHAVIOR OF THE LOWER ORGANISMS

processes of theorganism. Is it possible that interference with the physio-
logical processes may induce changes in other activities, —in chemical
processes, in growth, and the like, — and that one of these activities is
selected, as in behavior, through the fact that it relieves the interference
that caused the change?

There is some evidence for this possibility. Let us look, for example,
at regulative changes in the chemical activity of the organism, such as
we see in the acclimatization to poisons, in the responses to changes in
temperature, or in the adaptation of the digestive juices to the food.
What is the material from which the regulative conditions may be se-
lected? One of the general results of modern physical chemistry is
expressed by Ostwald (1902, p. 366) as follows: “In a given chemical
structure all processes that are so much as possible, are really taking
place, and they lead to the formation of all substances that can occur
at all.”” Some of these processes are taking place so slowly that they
escape usual observation; we notice only those that are conspicuous.
But in its enzymes the body possesses the means (as Ostwald sets forth)
of hastening any of these processes and delaying others, so that the gen-
eral character of the action shall be determined by the more rapid pro-
cess. Such enzymes are usually present in the body in inactive forms
(zymogens), which may be transformed into active enzymes by slight
chemical changes, thus altering fundamentally the course of the chemi-
cal processes in the organisms.

It is evident, then, that the organism has presented to it, by the condi-
tion just sketched, unlimited possibilities for the selection of different
chemical processes. The body is a great mass of the most varied chemi-
cals, and in this mass thousands of chemical processes, in every direction,
— all those indeed that are possible, — are occurring at all times. There
is then no difficulty as to the sufficiency of the material presented for
selection, if some means may be found for selecting it.

Further, it is known that interference with the physiological pro-
cesses does result in many changes in the internal activities of the organ-
ism, as well as in its external movements. Intense injurious stimula-
tion causes not merely excess movements of the body as a whole, but
induces marked changes in circulation, in respiration, in temperature,
in digestive processes, in excretion, and in other ways. Such marked
internal changes involve, and indeed are constituted by, alterations of
profound character in the chemical processes of the organism. These
chemical changes are sometimes demonstrated by the»production of new
chemicals under such circumstances. Furthermore, it is clear that the
internal changes due to interference with the physiological processes are
not stereotyped in character, but varied. Under violent injurious stimu-

REGULATION IN BEHAVIOR 347

lation, respiration becomes for a time rapid, then is almost suspended.
The heart beats for a time furiously, then feebly, and there is similar
variation in other internal symptoms.

Thus it seems clear that interference with the life processes does
produce varied activities in other ways than in bodily movements; and
that among these it results in varied chemical processes. ‘There is then
presented opportunity for regulation to occur in the same way as in
behavior. Certain of the processes occurring relieve the disturbance of
the physiological functions. There results a cessation of the changes.
In other words, a certain process is selected through the fact that it does
relieve. It is well known, through the work of Pawlow (1898), that the
adaptive changes in the activities of the digestive glands, fitting the
digestive juices to the food taken, do not occur at once and completely
under a given diet, but are brought about gradually. As the dog is
continued on a diet of bread, the pancreatic juice becomes more and
more adapted to the digestion of starch. ‘This slow adaptation is of
course what should be expected if the process occurs in anything like
the manner we have sketched.

At a later stage, if the laws of these processes are the same as those
for behavior, there will be present certain fixed methods of chemical
response, by which the organism reacts to certain sorts of stimulation.
That the law of the readier resolution of physiological states after repe-
tition holds in this field, is clearly indicated by the work of Pawlow. He
found that the pancreas under a uniform diet does tend to acquire ; a
fixed method of reaction to the introduction of the food, that is not
easily changed. In the dog which has digested starch for a month, the
pancreatic juice is not readily changed back to that adapted to the diges-
tion of meat. As a result, definite organs will in the course of time have
left open to them only certain limited possibilities of variation — due
to the development of something corresponding to the “‘action system”
in behavior. Thus, in the pancreas, there will not exist unlimited possi-
bilities as to the chemical changes that may occur. Its ‘“‘action system”’
will be limited perhaps to the production of varied quantities of a cer-
tain set of enzymes, — amylopsin, trypsin, etc. The proper selection
of these few possibilities will then occur by the method sketched. When
digestion is disturbed by food that is not well digested, variations in
the production of the different enzymes will be set in train, and one of
these will in time relieve the difficulty, through the more complete diges-
tion of the food. ‘Thereupon the variations will cease, since their cause
has disappeared. By still more complete fixation of the chemical re-
sponse, through the law of the readier resolution of physiological states
after repetition, or the analogue of this law, an organ or organism may

348 BEHAVIOR OF THE LOWER ORGANISMS

largely lose its power of varying its chemical behavior and thus be
unable to meet new conditions in a regulative way. A condition com-
parable to the production of a fixed reflex in behavior will result.

It is perhaps more difficult to apply the method of regulation above
set forth to processes of growth and regeneration. Yet there is no logi-
cal difficulty in the way. The only question would be that of fact, —
whether the varied growth processes necessary do, primitively, occur
under conditions that interfere with the physiological processes. When
a wound is made or an organ removed, is the growth process which
follows always of a certain stereotyped character, or are there variations?
It is well known, of course, that the latter is the case. In the regenera-
tion of the earthworm, Morgan (1897) finds great variation; he says
that in trying many experiments, one finds that what ninety-nine worms
cannot do in the way of regeneration, the one hundredth can. The
very great variations in the results of operations on eggs and young
stages of animals are well known. Removal of an organ is known to
produce great disturbance of most of the processes in the organism, and
among others in the process of growth.

It appears not impossible then that regulation may be brought about
in growth processes in accordance with the same principles as in be-
havior. A disturbance of the physiological processes results in varied
activities, and among these are varied growth activities. Some of these
relieve the disturbance; the variation then ceases and these processes
are continued. In any given highly organized animal or plant the dif-
ferent possibilities of growth will have become decidedly limited; and it
is only from this limited number of possibilities that selections can be
made. In some cases, by the fixation of certain processes through the
analogue of the law of the readier resolution of physiological states,
the organism or a certain part thereof will have lost the power of respond-
ing to injury save in one definite way. Under new conditions this one
way may not be regulatory, yet it may be the only response possible.
Thus may result the formation under certain conditions of heteromorphic
structures, —a tail in place of a head, or the like, from a part of the
body that (in normal development perhaps) is accustomed to produce
such an organ. This would again correspond to the production of a
fixed reflex action in behavior, even under circumstances where this
action is not regulatory.

It appears to the writer that the method of form regulation recently
set forth in a most suggestive paper by Holmes (1904) is in agreement
with the general method of regulation here set forth, and may be consid-
ered a working out of the details of the way in which growth regulation
might take place along these lines. Holmes has of course emphasized

REGULATION IN BEHAVIOR 349

other features of the process in a way that is not called for in the pres-
ent work.

Some suggestions as to the possibility of regulation along the line of
the selection of overproduced activities are found in J. Mark Baldwin’s
valuable collection of essays entitled “Evolution and Development.”

It may be noted that regulation in the manner we have set forth is
what in behavior is commonly called intelligence. If the same method
of regulation is found in other fields, then there is no reason for refusing
to compare the action there to intelligence. Comparison of the regu-
latory processes that are shown in internal physiological changes and in
regeneration, to intelligence seems to be looked upon sometimes as un-
scientific and heretical. Yet intelligence is a name applied to processes
that actually exist in the regulation of movement, and there is no a priori
reason why similar processes should not occur in regulation in other
fields. Movement is after all only the general result of the more recon-
dite chemical and physical changes occurring in organisms, and there-
fore cannot follow laws differing in essential character from the latter,
We are dealing in other fields with the same substance that is capable
of performing the processes seen in intelligent action, and these could
not occur as they do if the underlying physical and chemical pro-
cesses did not obey the same laws. In a purely objective consideration
there seems no reason to suppose that regulation in behavior (intelli-
gence) is of a fundamentally different character from regulation else-
where.

4. SUMMARY

We may sum up the fundamental features in the method of individ-
ual regulation above set forth as follows: —

The organism is a complex of many processes, of chemical change, of
growth, and of movement; these are proceeding with a certain energy.
These processes depend for their unimpeded course on their relations
to each other and on the relations to the environment which the pro-
cesses themselves bring about. When any of these processes are blocked
or disturbed, through a change in the relations to each other or the
environment, the energy overflows in other directions, producing varied
changes, —in movement, and apparently also in chemical and growth
processes. These changes of course vary the relations of the processes
to each other and to the environment; some of the conditions thus
reached relieve the interference which was the cause of the change.
Thereupon the changes cease, since there is no further cause for them;
the relieving condition is therefore maintained. After repetition of this
course of events, the process which leads to relief is reached more

350 BEHAVIOR OF THE LOWER ORGANISMS

directly, as a result of the law of the readier resolution of physiological
states after repetition. Thus are produced finally the stereotyped
changes often resulting from stimulation.

This method of regulation is clearly seen in behavior, where its
operation is, in the later stages, what is called intelligence. Its applica-
tion to chemical and form regulation is at present hypothetical, but
appears possible.

BIBLIOGRAPHY

THE following is a list of the works cited in the text. It is not a complete
bibliography of behavior in lower animals, but will be found to contain most of the
more important papers on the lowest groups. The authors’ names are given in
alphabetical order, with their works arranged according to the date of their appear-
ance. In the text the works are cited by the name of the author accompanied by
the date; for the complete title reference is to be made to the present list.

Apams, G. P., 1903. On the negative and positive phototropism of the earth-
worm Allolobophora fcetida (Sav.), as determined by light of different intensities:
Amer. Journ. Physiol., IX, 26-34. — ALLABACH, L. F., 1905. Some points regard-
ing the behavior of Metridium: Biol. Bul., X, 35-43.

Bain, ALEXANDER, 1888. The emotions and the will. 604 pp. London. —
~ Ip., 1894. The senses and the intellect. 3d ed. New York. — BAsianl, E. G.,
1861. Recherches sur les phénoménes sexuels des infusoires: Journ. Physiol.
(Brown-Séquard), IV, 102-130; 194-220; 431-448; 465-520 (also separate, Paris,
1862). — Ip., 1873. Observations sur le Didinium nasutum: Arch. d. Zool. Exp.,
II, 363-394. — BALDWIN, J. Mark, 1897. Mental development in the child and in
the race. Methods and processes. 2ded. 496 pp. New York. —Ib., 1902. De-
velopment and evolution. 395 pp. New York. — Bancrort, F. W., 1904. Note
on the galvanotropic reactions of the medusa Polyorchis penicillata A. Agassiz: Journ
Exp. Zool., I, 289-292. — Ib., 1905. Ueber die Giiltigkeit des Pfliiger’schen Gesetzes
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and reactions of Hydra: Quart. Journ. Micr. Sci., XLVIII, 585-622. — WALLEN-
GREN, H., 1902. Zur Kenntnis der Galvanotaxis. I. Die anodische Galvanotaxis:
Zeitschr. f. allg. Physiol., II, 341-384. — Ip., 1902 a. Inanitionserscheinungen der
Zelle: Zeitschr. f. allg. Physiol., I, 67-128.—In., 1903. Zur Kenntnis der Galvano-
taxis. II. Eine Analyse der Galvanotaxis bei Spirostomum: Zeitschr. f. allg. Physiol.,
II, 516-555. — WASMANN, E., 1901. Nervenphysiologie und Tierpsychologie:
Biol. Centralbl., XXI, 23-31. — Ip., 1905. Instinct und Intelligenz im Tierreich.
Dritte Auflage. 276 pp. Freiburg i. Br.— Witson, E. B., 1891. The helio-
tropism of Hydra: Amer. Naturalist, XXV, 413-433.

358 BEHAVIOR OF THE LOWER ORGANISMS

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Ip., 1903 a. The instincts, habits, and reactions of the green frog: Harvard Psychol.
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INDEX

Acclimatization to stimuli, in Amceba, 24;
in Paramecium, 52; in sea anemones,
207; general, 294; to heat, 101; to poisons,
346.

Accommodation, see adaptiveness and regu-
lation.

Acids, collection in, by Paramecium, 65, 67;
by other infusoria, 122.

Actinia, taking of food when cut in two,
227.

Actinians, see sea anemones.

Action system, Paramecium, 107; of infuso-
ria in general, 110; of Coelenterata, 189;
general, 300.

Activity, cause of, 284, 285.

Adams, behavior of earthworm, 248.

Adaptiveness of behavior, in Amoeba, 23; in
bacteria, 39; in Paramecium, 45, 79,
129; of changes of behavior in Stentor,
178; in food reactions of Gonionemus,
221; in ccelenterates, 230; in reactions
to representative stimuli, 296; general
factors, 299, 305, 338-350.

Adjustment, 342 (see adaptiveness and regu-
lation).

Aiptasia, reaction to local stimulation, 199;
setting of reaction by repetition, 206;
acclimatization to stimuli, 207; relation
to gravity, 211; food reactions, 223-226;
rapid contraction, 228.

Allabach, behavior of Metridium, 224.

Allolobophora, testing movements, 247.

Alternating electric currents, reaction to,
in Paramecium, 83.

Ameeba angulata, 5; proteus, 2, 12, 13;
velata, 5, 8; verrucosa, 2, 18.

Ameeba, structure, 1; movements, 2; behav-
ior and reactions, 6-25; food taking, 13-
19; relation of behavior to tropism
theory, 269; relation to reflexes, 279;
question of consciousness, 336.

Amylobacter, 30, 32, 38.

Anaérobic bacteria, 31, 341.

Analysis of behavior, 283-313.

Anode, movement toward, in Paramecium,
81, 85, 98; in Flagellata, 152; in Opa-
lina, 152, 159; in infusoria in general,
163.

Antholoba, attachment to crabs, 197.

Antitype, 277.

Anurea, reaction to electric current, 242.

Association, in hermit crabs, 257, 290; gen-
eral, 334.

Attached infusoria, reactions, 116; complex-
ity of behavior, 180.

Attention, 330.

Authorities cited, 351.

Avoiding reaction, in Paramecium, 47, 53;
adaptiveness of, 79; in Chilomonas, 111;
in Euglena, 112; in other flagellates, 113;
in other ciliates, 113; in light reactions,
149; relation to localization, 117; relation
to reflexes, 279.

Bacteria, structure, 26; movements, 26;
behavior and: reactions, 27-40; relation
of behavior to tropism theory, 271; rela-
tion to reflexes, 278; regulation in behav-
ior, 341.

Bacterium chlorinum, 37; megatherium, 34;
termo, 30, 32, 33, 34-

Bain, selection of overproduced movements,
302, 327.

Balantidium, reaction to chemicals, 122.

Balbiani, behavior of conjugating Paramecia,
104; use of trichocysts, 186.

Baldwin, law of dynamogenesis, 289; selec-
tion of overproduced movements, 302,
327; organic selection, 321, 326; regu-
lation, 349.

Bancroft, reaction of infusoria to electricity,
167; of medusz to electricity, 208, 210.

Barratt, reaction of Paramecia to chemicals,
64; theory of reaction to electricity (with
Coehn), 165.

Bell of medusa, independent contractility,
228.

Beer, Bethe, and v. Uexkiill, terminology,
275; reflex and antitype, 277.

Bethe, behavior of ants and bees, 258.

Bibliography, 35r.

Bilateral animals, relation of behavior to
tropism theory, 271, 273.

Binet, food habits of infusoria, 186.

Birukoff, reaction of Paramecium to induc-
tion shocks, 83, 88.

Blowfly larva, behavior, 249.

Bodo, reaction to chemicals, 124.

Bohn, behavior of hermit crabs, 211, 250; of
Convoluta, 254; of littoral animals, 255;
local action theory of tropisms, 274.

Botrydium, reactions to light, 143, 144.

359

360 INDEX

Bredig, properties of colloids, 317.

Brittle star, behavior 240.

Bryopsis swarm spores, reactions to light, 144.

Budgett, theory of reaction to electric cur-
rent (with Loeb), 166.

Bursaria, avoiding reaction, 114; reaction
to heat, 126, 305, 318, 322.

Calvert, Mrs. P. P., behavior of earthworm,
247.

Carbon dioxide, reaction to, in Paramecium,
67, 297; in other infusoria, 122.

Carchesium, 116; reaction to light, 142; ces-
sation of reaction to faint stimuli, 172.

Carcinus, habit formation, 256.

Carlgren, cause of reaction to electric cur-
rent, 165; ciliary action in sea anemones,
222.

Cataphoric action, part played in reaction
to electricity, 164.

Cathode, movement toward, in Paramecium,
80, 83; in flagellates, 152; in ciliates,
152; in Spirostomum, 157; in Opalina,
162; general, 163.

“Central nervous system” of medusz, 189.

Centrifugal force, reaction to, in Paramecium,
51, 78; in other infusoria, 150.

Cerianthus, movement when without food,
191; righting reactions, 195; reaction to
gravity, 195, 210; reaction of hetero-
morphic tentacles, 227.

Chain reflexes, 251.

Change of conditions as cause of reactions,
in Ameeba, 19; in bacteria, 29, 37; in
Paramecium, 51, 56, 58, 67, 108; in other
infusoria, 123; in reactions to light, 131,
133, 136, 141, 145, 215; general, 293,
333-

Chemical processes in organisms, 346.

Chemicals, reaction to, in Amoeba, 9; in
bacteria, 28-34; in Paramecium, 51, 53,
54, 62, 120; in Hydra, 198, 218; in me-
dusz, 220; in sea anemones, 224; inter-
ference with reaction to chemicals, 83,
96.

Chilomonas, structure and behavior, 111;
reaction to electric current, 152.

Chlamydomonas, reaction to light, 142, 146;
to gravity, 149; to centrifugal force, 150.

Choice, 330, 340; choice of food in infuso-
ria, 183.

Chromatium, reactions, 33, 35, 36.

Chromulina, reactions to gravity, 149; re-
versal by heat, 150. .

Chytridium, reaction to light, 142.

Cilia, in infusoria, 41; observation of move-
ments, 83; cathodic reversal under electric
current, 84; action in food taking of sea
anemones, 222; reversal in sea anemones,
223, 224, 227; cilia in sea urchin, 234.

Ciliata, 41.

Cnidaria, behavior of, 188-232.

Cnidocil, 218.

Coehn and Barratt, theory of reaction to elec-
tric current, 165.

Ceelenterata, behavior of, 188-232; reflexes
in, 133, 279; relation to tropism theory,
272.

Cold, reaction to, in bacteria, 37; in Para-
mecium, 51, 53, 70; in other infusoria,
124; effect on Hydra, 205.

Coleps, lack of reaction to gravity, 150.

Colloids, dependence of properties on his-
tory, 317, 334-

Color, reaction to, in Amoeba, 1x; in bac-
teria, 36, 341; in Euglena, 140; in Hydra,
212.

Colorless infusoria, usual lack of reaction to
light, 128; cases of reaction to light, 142,

333-

Colpidium, avoiding reaction, 115; collec-
tion in acids, 122; lack of reaction to grav-
ity, 150; reaction to electric current, 155.

Colpoda, lack of reaction to gravity, 150.

Combinations of stimuli, in infusoria, 92.

Compensatory movements, 75.

Conduction of stimulation, in ccelenterates,
228; in Protozoa, 262.

Condylactis, relation to gravity, 211.

Congenital variations, 319, 320.

Conjugation, behavior during, 102, 182.

Consciousness, 328, 334, 335, 340-

Contact reactions, in Amoeba, 6; in bacteria,
27, 37; in Paramecium, 51, 54, 59, 60;
in other infusoria, 117; interference
with other reactions, 92-96, 119, 133;
cause of interference, 120.

Contraction, in response to stimuli, in Para-
mecium, 89; in other infusoria, 114; in
Coelenterata, 197; spontaneous contrac-
tions in infusoria, 181; in Hydra, 189;
in meduse, 191; rapid contraction in
Aiptasia, 228; local contractions in ccelen-
terates, 231; relation to tropism theory,
272; setting of contractions through repe-
tition in sea anemones, 206.

Convoluta, habit formation, 255, 333; depen-
dence of reaction to gravity on past his-
tory, 258.

Correlation of behavior in different parts of
ceelenterate body, 227, 229; in sea urchin,
252; in starfish, 239.

Corymorpha, reaction to gravity, 210; reac-
tion of tentacles, 222.

Crab, habit formation, 256, 290.

Crayfish, habit formation, 255, 290.

Creeping infusoria, reactions, 114; complex-
ity of behavior, 180.

Crustacea, habit formation, 255, 290, 333-

Cryptomonas, reaction to light, 142, 143, 146;
to electric current, 152.

Currents, protoplasmic, in Amoeba, 4; cur-
rents due to cilia in infusoria, 46, 60, 131};
observation of these currents, 83; cur-

INDEX

rents in reaction to electricity, 85; reac-
tion to water currents in Paramecium, 73.
Cutleria swarm spores, reaction to light, 142,
146.
Cyclidium, collection in acids, 122.
Cysts of Euglena, as food for Ameeba, 12.

Daily life of Paramecium, 104.

Dale, reaction of infusoria to water currents,
75; to chemicals, 122.

Davenport, reaction of Amoeba to light, 11,
21; of Paramecium to gravity, 76; of in-
fusoria to chemicals, 122; diagram of
tropism theory, 268; terminology, 275.

Desire, 331.

Development of behavior, 314-327-

Didinium, food habits, 91, 185; discharge of
trichocysts, 186.

Discrimination, 304, 315, 329.

Driesch, chain reflexes, 251; tropism theory,
266; reflex, 278; vitalism, 338.

Driving Ameeba, 6.

Drying, reaction to, in flatworm, 243.

Earthworm, testing movements, - 247;
tion to light, 248.

Echinoderms, behavior, 234, 238;
to tropism theory, 272.

Ectosare, 2, 43; contractionin Paramecium, 89.

Electricity, reaction to, in Amceba, 12, 23, 24;
in bacteria, 37; in Paramecium, 51, 80
(induction shocks, 81; alternating cur-
rents, 83, 87; constant current, 83; inter-
ference with reaction to electricity, 94, 96,
119); in’ other infusoria, 151 (induction
shocks, 151; constant current, 152);
lack of reaction in Euglena, 152; reaction
in Colpidium, 155; in Spirostomum, 157;
in Opalina, 159; summary on infusoria,
163; theories, 164; reaction in ccelen-
terates, 208; in rotifers, 242; agreement
with tropism theory in infusoria, 271.

Elemental life, 260.

Endosarc, 2, 43.

Engelmann, reaction of Pelomyxa to light,
11; behavior of bacteria, 30, 35, 36, 39;
reaction of Euglena to shading parts of
body, 136; reaction to light in Parame-
cium bursaria, 142; terminology, 275.

Epistylis, reaction to ultra-violet light, 142;
cessation of reaction to weak stimuli, 172.

Ether, collection of bacteria in, 33.

Euglena, structure and reactions, 102, 134;
reactions to light, 134, 294; spiral path,
138; reaction to gravity, 149; to centrifu-
gal force, 150; no reaction to electric
current, 152.

Exploratory movements, in Lacrymaria, 181;
in Hydra, 189, 204; in medusw, 220; in
sea anemones, 222; in Planaria, 243-
245; in other invertebrates, 246-250
(see trial movements).

reac-

relation

361

Famintzin, reaction of flagellates to light,
140.

Fatigue, in infusoria, 100, 172; general, 331.

Fear, 332.

Fern spermatozoids, reaction method, 121;
Weber’s law, 123.

Final causes, 344.

“Fishing” in Gonionemus, 192, 211, 214.

Fission, behavior during, 102.

Flagella, in bacteria, 26; in infusoria, 41, 60,
Itt.

Flagellata, 41; movements and reactions,
111; reactions to electricity, 119, 152.
Flatworm, localization of reactions, 236;
testing movements, 243; righting reac-
tion, 245; physiological states, 253;

habit formation, 254.

Food, behavior in obtaining, Amoeba, 12-
19, 24, 25; Paramecium, 46, 183; Sten-
tor, 171; in other infusoria, 118, 182;
Gonionemus, 192, 219; in ccelenterates
in general, 216; Hydra, 216; medusz,
219; sea anemones, 221; sea urchin,
235; flatworm, 246; mollusk (Nassa),
247; food habits in general, 331; lack of
food, in infusoria, 101; in Hydra, 189;
in Cerianthus, 196; rejection of food in
sea anemones, 202; relation of food
reactions to reaction to light, in parasitic
infusoria, 142; in Hydra, 213.

Form regulation, 348.

Free infusoria, simplicity of behavior, 180.

Gamble and Keeble, behavior of Convoluta,

255.

Garrey, kinesis, 275.

Gonionemus, “fishing,” 192; relation to
gravity, 211; reaction to light, 214;

food reactions, 219; chemical stimuli,
220; mechanical stimuli, 220; reactions
of separated parts, 227; adaptiveness of
reactions, 221, 230.

Gravity, reaction to, in bacteria, 37; in Para-
mecium, 51, 75; in other infusoria, 150;
interference with, in infusoria, 96, 150;
reaction in coelenterates, 195, 210; in
hermit crabs, 211; in Convoluta, 255; de-
pendence on experience in Convoluta,
258; general effects of gravity on organ-
isms, 211. :

Growth, regulation of, 348.

Habit, 333.

Habit formation, sea anemone (?), 207;
starfish, 241; Convoluta (flatworm), 254;
Crustacea, 255; retention of habit, 256.

Hematococcus, reaction to light, 142, 146;
to gravity, 149.

Halteria, reaction, 115.

Harper, behavior of earthworm, 247, 248.

Harrington and Leaming, reaction of Amceba
to light, 11, 20, 24.

362 _ INDEX

Heat, reaction to, in Amoeba, 10; in bac-
teria, 37; in Paramecium, §1~53, 79, 305;
in other infusoria, 124, 305; in Hydra,
204; in rotifers, 242; in flatworms, 244;
interference with other reactions, 150;
interference of other reactions with reac-
tion to heat, 93.

Hermit crabs, temporary reaction to gravity,
211; seeking shells, 250; formation of
association and habit, 257, 290.

Hertel, reactions to ultra-violet light, in
Paramecium, 72; in other infusoria, 142;
in Hydra, 213.

Heteromorphic tentacles, behavior, 227.

Hobhouse, reflex, 278; selection from varied
movements, 327.

Hodge and Aikins, changes in behavior in
Vorticella, 179; duration of modifica-
tion, 254; continuous activity of Vorti-
cella, 181.

Holmes, trial movements in lower animals,
247-250; random movements, 251, 254;
form regulation, 348.

Holt and Lee, tropism theory in reactions to
light, 266, 269.

Hunger, infusoria, 101; Hydra, 189, 205, 219;
sea anemones, 191, 224; Planaria, 253; in-
vertebrates in general, 252; general, 295,
331-

Hunter ciliates, 184.

Hydra, nervous system, 189; rhythmic ac-
tivity, 189, 285; locomotion, 190; posi-
tion, 193; righting reaction, 193; local
contractions, 198, 272; locomotor reac-
tions, 203; reactions to electric current,
208; to light, 212; to chemicals, 198,
218; food reactions, 217; nematocyst
discharge, 218; hunger, 219.

Hydroid, reaction to gravity, 210; reaction
of tentacles, 222.

Hydromedusz, reactions of separated mar-
gin and bell, 227 (see meduse).

Hypotricha, reaction method, 53, 114; creep-
ing, 118; reaction to heat and cold, 124;
to electricity, 154.

Independence of parts of body, in ccelen-
terates, 227; in sea urchin, 235.

Individual selection, relation to natural selec-
tion, 324.

Induction shocks, reaction to, infusoria, 81,
102, 104, 151; ccelenterates, 208.

Infusoria, 41; behavior, 41-187; behavior
under natural conditions, 179; food
habits, 183; relation to tropism, 270.

Inhibition, release of, as determining move-
ment, 284.

Injury, relation of reactions to, in Amceba,
23; in bacteria, 33; in Paramecium, 52,
63, 109 (see regulation, and interference
with processes).

Instincts, 237.

Intelligence, 334, 343; relation to natural
selection, 324, 345; to regulation, 349,
359

Interference with internal processes as cause
of reaction, in Amoeba, 11, 20; in bac-
teria, 39, 341; general, 295, 342, 346;
interference of stimuli, 92, 119, 150.

Internal factors in behavior, 283.

Invertebrates, lower, general features of be-
havior, 233-259.

James, reflex, 278, 280, 281.

Jellyfish, see meduse.

Jensen, reactions to gravity in infusoria, 76,
149.

Kinesis, 275.
Kiihne, polarizing effects of electric current,
167.

Lacrymaria, reaction to induction shock,
151; trial movements, 181.

Lagynus, food habits, 187.

Le Dantec, life processes of Protozoa and
Metazoa, 260.

Learning, relation of change of behavior in
infusoria to, 178; in crustaceans, 255.

Leech, trial movements, 247; reaction to
light, 248.

Leidy, taking food in Ameceba, 15, 19.

Light, reaction to, Amoeba, 11; _ bacteria,
35-37, 341; Paramecium, 72; Stentor, 128;
Euglena, 134; other infusoria, 141;
swarm spores, 143; Coelenterata, 212;
Hydra, 212; Gonionemus, 214; Roti-
fera, 242; earthworm, 247; leech, 248;
blowfly larva, 249; in colorless organ-
isms, 142, 213, 333; tropism theory for
light reactions, 266, 268, 269.

Literature list, 351.

Localization of reactions, in Ameeba, 20;
Paramecium, 51, 52; in other infusoria,
117; different methods, 307; relation to
tropism theory, 266, 274.

Localized reactions in ccelenterates, 198, 231;
in theory of tropisms, 266, 274.

Locomotion, in Hydra, 191; in sea anemones,
I9l.

Locomotor reactions in Ccelenterata, 203.

Loeb, behavior of Cerianthus, 191, 195;
localization in medusz, 200; indepen-
dent activity of parts of body in Ceelen-
terata, 227, 228; function of nervous
system in meduse, 229; chain reflexes,
251; function of nervous system, 263;
tropism theory, 266, 269.

Loeb and Budgett, theory of reaction to elec-
tricity, 166.

Loxocephalus, spontaneous collections, 122.

Loxodes, avoiding reaction, 113.

Loxophyllum, avoiding reaction, 113.

Ludloff, reactions to electricity, 84, 167.

INDEX

7
Lyon, reaction to currents, 74; to gravity,
77; to centrifugal force, 78.

Manubrium, localizing reactions, 200; food
reactions, 220; independent reactions,
927.

Massart, reactions of bacteria, 34, 37; dis-
charge of trichocysts, 90; interference of
heat and contact reactions, 93; reaction
of Polytoma, 123; reversal of reaction to
gravity by heat, 150; nomenclature, 275.

Mast, reactions of bacteria, 37; local stimu-
lation with heat, 198; behavior of Hydra,
203, 205; reaction of flatworm to heat, 245.

Maupas, food habits of infusoria, 182, 186.

Mechanical stimulation, in Amoeba, 6; in™

bacteria, 27, 37; in Paramecium, 51, 54,
59; in other infusoria, 117; in Hydra,
204; in medusz, 220; interference with
other stimuli in infusoria, 92-96.

Medusez, nervous system, 189; rhythmical
contractions, 191, 227; food habits, 192,
219; reaction to local stimulation, 199,
200; reaction to electric current, 210;
to gravity, 211; to light, 214; to chemi-
cals, 220; behavior of separated pieces,
227; relation of behavior to tropism the-
ory, 272.

Memory, 333:

Mendelssohn, temperature reactions, 70;
optimum for infusoria, 127; change of
optimum, ror.

Metabolism, relation of behavior to, in bac-
teria, 36, 39; in Ccelenterata, 231; in
invertebrates in general, 251; relation to
movement, 284; relation to changes in
physiological state, 286, 287; relation to
positive reactions, 295; general, 299,
349, 341.

Metazoa and Protozoa, 188; comparison of
behavior, 260-264.

Metridium, movement from internal causes,
191; relation to gravity, 211; food reac-
tions, 222, 224, 225; fatigue, 226; reac-
tions of separated tentacles, 227.

Microthorax, avoiding reaction, 115.

Miyoshi, reactions of bacteria, 32.

Modifiability of behavior, Amoeba, 24; bac-
teria, 39; Paramecium, 100; Stentor,
170; sea anemones, 206, 207, 226; Cc-
lenterata, 231, 232; invertebrates, 237,
250; Convoluta (flatworm), 255; Crus-
tacea, 255-257; higher invertebrates,
258; general, 258, 317; laws of, 286-291;
modifiability in colloids, 317.

Moebius, behavior of Nassa, 247.

Mollusks, trial movements, 247.

Monas, reaction to light, 36.

Moore, reactions of infusoria to gravity, 77,
96; lack of food, ror.

Morgan, C. L., trial and error in higher ani-
mals, 250.

363

Morgan, T. H., variability in regeneration,

348.

Motile touch, reaction of Gonionemus to,
221, 230.

Movement spontaneous, 283; cause of,
284, 285.

Myxomycetes, reaction to light, 12.

Naegeli, movement and reactions of flagel-
lates, 111, 113; spiral movement in swarm
spores, 143.

Nagel, food reactions in sea anemones, 224.

Nassa, behavior in finding food, 247.

Natural selection, 320; relation to individ-
ual selection or intelligence, 324, 325, 345;
part played in behavior, 327.

Negative reaction, in Amoeba, 6, 23; in
bacteria, 27, 28; in infusoria, 53, 117;
general, 301.

Nematocysts, action in food taking, 218.

Nervous system, of Coelenterata, 189; con-
duction by, “in ccelenterates, 228; func-
tion in coelenterates, 230; specific prop-
erties and general functions, 260-264;
behavior without a nervous system, 26r.

Nomenclature, 274-276.

Nucleus, in Amoeba, 2; in Paramecium, 43.

Nutritive processes, relation of behavior to,
see metabolism.

Nyctotherus, avoiding reaction, 114;
tion to chemicals, 122.

reac-

Oltmanns, terminology, 275.

Opalina, avoiding reaction, 114; reaction to
chemicals, 122; to electric current, 156,
159.

Ophidomonas, reaction to light, 36.

Ophryoglena, lack of reaction to gravity, 150.

Optimum, in bacteria, 31; Paramecium,
56, 66; for temperature, 71, 127; change
of optimum, 1o1; optimum in other in-
fusoria, 123, 127; optimum in light reac-
tions, 141, 148; general, 295.

Organic selection, 321.

Orientation, Amoeba, 22, 269; Paramecium,
73 (by exclusion, 72); relation between
orientation reactions and others in infuso-
ria, 78; no position of symmetry in infu-
soria, 79; orientation by exclusion in
Oxytricha, 126; orientation to light, 134,
138-140; to electric current, 153, ‘163;
in rotifera, 242; orientation to light in
earthworm, 247, 248; in blowfly larva,
249; fundamental feature in tropism,
264; how brought about, 267.

Oscillaria, as food for Amoeba, ro.

Osmotic pressure, reaction to, in bacteria,
34; in Paramecium, 63; in other infuso-
ria, 124.

Ostwald, chemical processes in organisms,
346.

Oxygen, reaction to, bacteria, 28-31, 39, 3413

364

Paramecium, 66, 340; infusoria in gen-
eral, 124; Hydra, 216; relation to reac-
tion to light in Paramecium bursaria, 142;
general, 340.

Oxytricha, avoiding reaction, 114; sponta-
neous collections, 122; reaction to heat
and cold, 125; transverse position in
electric current, 154.

Pain, 332, 349.

Paramecium, structure, 41; movements, 44;
behavior and reactions, 44-109; relation
of behavior to reflexes, 279; relation to
consciousness, 336.

Paramecium bursaria, reaction to light, 142,
340; to gravity, 149.

Parasitic infusoria, reaction to light, 142, 333.

Parker, reversal of cilia in sea anemones,
224; reaction of separate parts, 227;
conduction of stimulation, 229.

Parker and Arkin, behavior of earthworm, 248.

Pawlow, modifiability of action in digestive
glands, 347.

Pearl, reaction to electric current, Chilomo-
nas, 152; Colpidium, 155; Hydra, 208;
cause of reaction to electric current, 165;
behavior of Planaria, 236, 243, 245, 253,
273.

Pedicellarie, 234; behavior, 235, 238.

Pelomyxa, reaction to light, 11.

Penard, movements of Amceba, 6, 8.

Perception, 329. .

Pericheta, reaction to light, 248.

Peridinium, reaction to electric current, 152.

Perkins, behavior of Gonionemus, 192.

Pfeffer, behavior of bacteria, 32, 33, 34, 38;
of fern spermatozoids and _ flagellates,
123, 124; tropisms, 275; nomenclature,

275.

Physiological states, dependence of behav-
ior on, Stentor, 178; ccelenterates, 229,
231; invertebrates in general, 251; flat-
worm, 253; Protozoa and Metazoa, 263;
higher animals and man, 331; relation to
reflexes, 282; changes of physiological
state, 287; law of change, 291; develop-
ment in physiological states, 316; gen-
eral, 286-291.

Planaria, localization of reaction, 236; test-
ing movements, 243; righting reaction,
245; physiological states, 253; relation
to tropism theory, 273.

Plasmolysis, 34.

Pleasure, 332, 340.

Pleuronema, reaction method, 115; reaction
to light, 142.

Poisons, collection of bacteria in, 33.

Polarizing effect of electric current, 167.

Polyorchis, reaction to electric current, 210.

Polytoma, reaction to chemicals, 123; to
gravity, 149.

Polytomella, reaction to electric current, 152.

INDEX

Positive reaction, in Amoeba, 8, 23; bacteria,
28; Paramecium, 54, 60, 65; in other
infusoria, 121; general, 295, 309.

Preyer, behavior of starfish, 239; habit for-
mation in starfish, 241; varied physio-
logical states, 253.

Prism, Strasburger’s experiments with, 145.

Protozoa, behavior, 1-187; reflexes in, 233;
relation to tropism theory, 269-271;
comparison with behavior of Metazoa,
260-264.

Pseudopodia, 1, 4; reaction of single one, r5-

Psychic behavior, relation to behavior of
lower organisms, 329.

Purpose, 343-

Piitter, interference of heat and contact reac-
tions, 93; of contact and reaction to elec-
tricity, 119; variability of contact reac-
tion, 100; symptomatology, 300.

Quieting infusoria, 81, 83.

Radl, reaction to gravity, 77; theory of
tropisms in reaction to light, 274.

Random movements, 251, 254 (see érial move-
ments).

Reaction, 6, 283.

Reflexes, 232; in Protozoa and Ceelente-
rata, 233; in sea urchin, 234, 235; in star-
fish, 236; in flatworm, 236, 254; in higher
animals, 237; relation to modifiability,
258; definition, 277; part played in be-
havior of lower animals, 277-282.

Regeneration, variation in processes, 348.

Regulation, 299, 301; how brought about in be-
havior, 338-350; in other fields, 345; in
chemical processes, 346; in growth, 348;
non-regulatory behavior, 345 (see adap-
tiveness).

Rejecting reaction of sea anemones, 202.

Rejection of unsuitable food, in infusoria,
183; in sea anemones, 202.

Representative stimuli, 296, 316, 333.

**Republic of reflexes,” 235.

Resolution of physiological states, law of,
291, 314, 334; part played in regulation,
43-

Rariietioe. relation of habits to, in Parame-
cium bursaria, 142, 340; in Hydra, 216.

Reversal of reactions, as stimulus becomes
stronger, 262 (see optimum); reversal of
cilia in sea anemones, 224.

Rhumbler, currents in Amoeba, 4, 5; reac-
tions of Amoeba to food, 11, 19, 20, 25.

Rhythmical contractions, in Vorticella, 181; in
Hydra, 189; in medusa, 191; in margins
and bell of meduse when separated, 227;
rhythmical activity of Convoluta as habit,
255.

Righting reaction, in Hydra, 193; in sea
anemones, 195; in starfish, 239; in flat-
worm, 245.

INDEX

Roesle, reaction to induction shocks in infu-
soria, 82, I51.

Rolling movement in Ameeba, 2.

Romanes, localization in medusa, 200; reac-
tion of parts of meduse, 227; nervous
conduction in medusz, 228, 229; behav-
ior of starfish, 241.

Rothert, reactions of bacteria, 31, 32, 373
reaction method in flagellates, 121; kine-
sis, 275.

Rotifera, avoiding reaction, 236;
to stimuli, 242.

Roux, polarizing effect of electric current,
167.

reactions

Sagartia, reaction to gravity, 196, 210; to
local stimulation, 199; finding food, 222;
taking indifferent bodies, 224; reactions
of separate tentacles, 227.

Saprolegnia, swarm spores, reaction method,
121.

Schwarz, reaction to centrifugal force, 150.

Sea anemones, nervous system, 189; loco-
motion, 191; effects of hunger, 191;
righting reaction, 195; reaction to grav-
ity, 195, 210; attachment to crab, 197;
localized reactions, 199; rejecting reac-
tion, 202; direction of movement, 206;
setting of reaction by repetition, 206;
acclimatization to stimuli, 207; food
habits, 221; part played by cilia, 222.

Sea urchin, reflexes, 234; reaction by varied
movement, 238; dependence of behavior
on physiological states, 252; modifiability
of behavior, 252.

Selection of conditions resulting from varied
movements, Amoeba, 22; bacteria, 40;
Paramecium, 79, 108; flagellates, 112;
ciliates, 115; coelenterates, 230; in in-
vertebrata in general, 238; rotifers, 242;
flatworms, 246; in Protozoa and Metazoa,
263; production of regulation, 339, 342;
general, 302.

Sensitiveness of different parts of body, in
infusoria, 59, 82, 117, 133, 136; compari-
son with sense organ, 262.

Simultaneous stimuli, effect on infusoria, 92,
180,

Sleep, 331.

Smith, behavior of earthworm, 247, 254.

Solids, reaction to, Amoeba, 6; bacteria, 27,
37; Paramecium, 51, 54, 59-62; other
infusoria, 117; interference with other
reactions, 92-96, 119.

Sosnowski, reactions of infusoria to gravity,
77, 96.

Spaulding, association and habit formation
in hermit crabs, 257; reflex, 282.

Spectrum, behavior of bacteria in, 36; of Eu-
glena, 140.

Spencer, selection of overproduced move-
ments, 302, 327.

305

Spermatozoids of fern, reaction method, 121;
Weber’s law, 123.

Spiral movement, bacteria, 27; Paramecium,
44, 46, 58; other infusoria, 110; flagel-
lates, 111; Swarm spores, 143; effect on
relation to light, 133, 138.

Spirillum, behavior, 27-29, 33, 34.

Spirostomum, avoiding reaction, 114; at-
tachment by mucus, 116, 118; relation
to gravity, 149; reaction to induction
shocks, 151; to constant current, 157.

Spontaneous activity, in Protozoa and Meta-
zoa, 261; in ccelenterates, 189; general,
283; spontaneous collections of infusoria,
68, 122.

Starfish, reflexes, 236;
239; righting reaction, 238;
reaction by repetition, 241.

Statkewitsch, reaction of Paramecium to
water current, 75; reaction to induction
shocks, 81, 83, 88, 151; to constant cur-
rent, 84; to alternating currents, 87;
quieting infusoria, 81, 83; discharge of
trichocysts, 90, 104; cataphoric action,
165; cause of reaction to electric current,
167.

Stentor, avoiding reaction, 113; attached
Stentors, 116; reaction to light, 128, 142;
behavior when attached, 171; modifica-
tion of reactions, 171-179, 333; tube
formation, 176; choice of food, 183;
relation of behavior to reflexes, 279;
changes in physiological state, 287; laws
of change, 290.

Stimuli, 6, 293.

Stoichactis, rejecting reaction, 201; reaction
to gravity, 211; food reactions, 223-226.

Strasburger, reaction method in swarm spores,
113; reaction of swarm spores to light,
143; experiments with prism, 145; ter-
minology, 275.

Stylonychia, avoiding reaction, 114; creep-
ing on surface, 118; reaction to electric
current, 154; food habits, 184.

Subjective states, 328, 331.

Summation of stimuli in Protozoa, 83, 262.

Surface tension, currents due to, 4.

Swarm spores, reaction method, 113; reac-
tion to light, 142, 143. E

variable reactions,
setting of

Temperature reactions, Amceba, 10; _ bacteria,
37, Paramecium, 51, 54, 55, 70; other infu-
soria, 124; interference with temperature
reactions, 93; optimum in infusoria, 127;
reaction in Hydra, 204; in flatworm, 243.

Tentacles, stimulation of, Hydra, 198; sea
anemones, 199; meduse, 200; methods
of contraction and bending, 198, 199;
movements in medus@, 220; in sea anem-
ones, 222; behavior of separated tenta-
cles, 227.

Terms employed in animal behavior, 274,

306 INDEX

Thorndike, trial and error in higher animals,
250.

- Tiaropsis, localizing reaction, 200.

Titchener, objective criteria of conscious-
ness, 278.

Tonus, 252, 263.

Torrey, behavior of Sagartia, 196, 199, 210,
222, 224, 227; of Corymorpha, 210, 222.

Trachelomonas, reaction to electric current,
152.

Tradescantia cells, effect of electric current,
167.

Transverse position, of Paramecia in alter-
nating electric currents, 87; in constant
current, 95; of Hypotricha in constant
current, 154; of Spirostomum, 158; in-
fusoria in general, 163.

Trepomonas, reaction method, 121.

Trial movements, Amceba, 22; Paramecium,
48, 106, 108; Stentor, 177; Lacrymaria,
181; in hunter ciliates, 186; Hydra, 204;
meduse, 220; sea anemones, 222; Cce-
lenterata in general, 230; in inverte-
brates in general, 238, 240, 251; flatworms,
243, 245, 246; earthworm, 247; leech, 248;
blowfly larve, 249; hermit crabs, 250;
higher animals, 250, 272; general, 305;
339, 342-

Trichocysts, 43; discharge, 90, 82, 186; func-

tion, go.

Tropisms, 237; local action theory of, 265-
274; various definitions, 274, 275.

Tube, of Stentor, 170; formation of, 176;
in other infusoria, 181.

Vexkiill, v., behavior of sea urchin, 234, 238,
252; reflex, 281.

Ultra-red light, reaction of bacteria to, 36;
ultra-violet light, reaction to, 72, 142.

Ulva, swarm spores, reaction to light, 143, 144.

Urocenirial attachment by mucus, 116,
118.
Urostyla, reaction to gravity, 149.

Variability in reactions, bacteria, 38; Para-
mecium, 49, 98, 279; other infusoria, 123;
Stentor, 176; coelenterates, 231; cs
derms, 238, 239.

Variations, individual, in behavior, 319, 321.

Verworn, reaction of Ameeba to electricity,
24; reaction of Pleuronema to light, 142;
of flagellates to electricity, 152; theory
of reaction to electricity, 167; tropism the-
ory, 266, 267, 269.

Vitalism, 338, 344.

Vorticella, 116; changes in reactions, 179;
duration of modifications, 179, 254;
spontaneous contractions, 181, 285, 286;
no periods of rest, 181, 284; rejection of
unsuitable food, 184.

Wagner, behavior of Hydra, 191, 203, 217.

Wallengren, lack of food in infusoria, ror;
lack of salts, 101; reaction to electric
current in Spirostomum, 157; in Opa-
lina, 1509.

Water currents, reaction to, in Paramecium,

73-

Weber’s law, in bacteria, 38; in fern sperma-
tozoids, 123; general, 294.

Wilson, reaction of Hydra to light, 212; to
oxygen, 216; food reactions, 219.

Wundt, reflex, 278.

Yerkes, behavior of Gonionemus, 192, 211,
214, 219, 227; habit formation in Crus-
tacea, 255; nomenclature, 275; modi-
fiability of behavior, 290, 291.

Yerkes and Huggins, habit formation in
Crustacea, 255.

LIBRARY

UNIVERSITY OF TORONTO

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