HARVARD UNIVERSITY

Library of the

Museum of

Comparative Zoology

HARVARD UNIVERSITY

Library of the

Museum of

Comparative Zoology

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THE INTERNATIONAL SCIENTIPIC SERIES.

JELLY-FISH, STAR-FISH
AND SEA-URCHINS

BEING

A RESEARCH ON PRIMITIVE NERVOUS SYSTEMS

BY

G. J. ROMANES, 31. A., LL. D., F. R. S.

ZOOLOGICAL SECEETAEY OF THK LISXEAX SOCIETT

NEW YORK:
D. APPLETOX AND COMPANY,

1, 3, AND 5 BO^'D STREET.

1893.

■J ■'

^^;

L/BRARV
DEC 2 2 1999

UNfVERsjTv

BIOLOGICAL LABORATORIES LIBRAITI
hlAfty/\RD UNIVERSITY

PREFACE.

When I first accepted the invitation of the editors
of the International Scientific Series to supply a
book upon Primitive Nervous Systems, I intended
to have supplemented the description of my own
work on the physiology of the Medusce and
Echinodermata with a tolerably full exposition of
the results which have been obtained by other
inquirers concerning the morphology and develop-
ment of these animals. But it soon became
apparent that it would be impossible, within the
limits assigned to me, to do justice to the more
important investigations upon these matters ; and
therefore I eventually decided upon restricting this
essay to an account of my own researches.

With the exception of a few Avoodcuts in the
last chapter (for the loan of which I am indebted
to the kindness of Messrs. Cassell), all the illustra-
tions are either original or copies of those in my
Royal Society papers. In the letter-press also I
have not scrupled to draw upon these papers.

X PREFACE.

wlierever it seemed to me that the passages would
})e suihciently intelligible to a general reader.
I may observe, however, that although I ha\-o
throughout kept in view the requirements of a
general reader, I have also sought to render the
book of service to the working physiologist, by
brinsfinix tooether in one consecuti\ e account all the
more important observations and results which
liave been yielded by this research.

G. J. R.

IX)NDON, 1884.

CONTENTS,

CHAPTKR PACK

Introduction ... ,„ ... „, ,„ 1

I. Structure of the RlEDusiE ,,, .., 10

II. Fundamental Experiments ... ... ... 26

III. Experiments in Stimulation ... ... 87

IV. Experiments in Section of Covered-Eyed ^Iedus^ 05
V. Experiments in Section of Naked-Eyed INIedus^ 104

VI. Co-ordination... ... ... ... ... i;>0

VII. Natural Rhythm ... ,,, ,„ ... 14G

VIH- Artificial Rhythm ... ... „, ... 175

IX. Poisons ... ... ... .„ ... 218

X. Star-Fish and Ska-Ueciiins ,„ „, ... 251

JELLY-FISH, STAR-FISH, AND
SEA-UECHLNS.

INTRODUCTION.

Among the most beautiful, as well as the most
common, of the marine animals which are to be met
Avith upon our coasts are the jelly-fish and the star-
fish. Scarcely any one is so devoid of the instincts
either of the artist or of tlie naturalist as not to
have watched these animals with blended emotions
of the ?esthctic and the scientific — feeling the beauty
while wondering at the organization. How many
of us who live for most of the year in the fog and
dust of large towns enjoy with the greater zest our
summer's holiday at the seaside ? And in the
memories of most of us is there not associated with
the picture of breaking waves and sea-birds floating
indiffeiently in the blue sky or on the water still
more blue, the thoughts of many a ramble among
the weedy rocks and living pools, where for the
time being we all become naturalists, and where
those who least know what they are likely to find

2 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

in tlieir search are most Lkely to approach the keen
happiness of cliiklhood ? If so, the image of the red
sea-stars bespangling a mile of shining sand, or
decorating the darkness of a thousand grottoes,
must be joined with the image, no less vivid, of
those crystal globes pulsating with life and gleam-
ino- with all the colours of the rainbow, which are
perhaps the most strange, and certainly in my
estimation the most delicately lovely creatures in
the world.

It is with these two kinds of creatures that the
present work is concerned, and if it seems almost
impious to lay the " forced fingers rude " of science
upon living things of such exquisite beauty, let it
be remembered that our human nature is not so
much out of joint that the rational desire to know
is incompatible with the emotional impulse to
admire. Speaking for myself, I can testify that my
admiration of the extreme beauty of these animals
has been greatly enhanced —or rather I should say
that this extreme beauty has been, so to speak,-
revealed — by the continuous and close observation
which many of my experiments required : both
with the unassisted eye and with the mici'oscope
numberless points of detail, unnoticed before, became
familiar to the mind; the forms as a whole were
impressed upon the memory; and, by constantly
watching their movements and changes of appear-
ance, I have grown, like an artist studying a face
or a landscape, to appreciate a fulness of beauty, the
esse of which is only rendered possible by the pc9'
ci'pi of such attention as is demanded by scientiiic

INTRODUCTION. 3

research. Moreover, association, if not the sole
creator, is at least a most important factor of
the beautiful; and therefore the sight of one ol
these animals is now much more to me, in the
respects which we are considering, than it can be
to any one in whose memory it is not connected
with many days of that purest form of enjoy-
ment which cfin only be experienced in the pursuit
of science.

And here I may observe that the worker in
marine zoology has one great advantage over his
other scientific brethren. Apart from the intrinsic
boaut}^ of most of the creatures with which he has
to deal, all the accompaniments of his work are
resthetic, and removed from those more or less
offensive features which cire so often necessaril}*
incidental to the study of anatomy and physiolog}'
in the higher animals. When, for instance, I con-
trast my oAvn work in a town laboratory on
vertebrated animals with that which I am now
about to describe upon the invertebrated in a
laboratory set up upon the sea-beach, it is im-
possible not to feel that the contrast in point of
enjoyment is considerable. In the latter case, a
summer's work resembles the pleasure-making of a
picnic prolonged for months, with the sense of feel-,
ing all the while that no time is being profitlessly
spent. Whether one is sailing about upon the
sunny sea, fishing with muslin nets for the surface
fauna, or steaming away far from shore to dredge
for othermaterial, or, again, carrying on observations
in the cool sea-water tanks and bell-jars of a neat

^ JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

little wooJen worksliop thrown open to the sea-
breezes, it alike requires some effort to persuade
one's self that the occupation is really something
more than that of finding amusement.

It is now twelve years since I first took to this
kind of summer recreation, and during that time
most of my attention while at the seaside has been
devoted to the two classes of animals already men-
tioned— viz. the jelly-fish and star-fish, or, as
naturalists have named them, the Medusie and
Echinodermata. The present volume contains a
tolerably full account of the results which during
six of these summers I have succeeded in obtaining.
If any of my readers should thiidc that the harvest
appears to be a small one in relation to the time
and labour spent in gathering it, I shall feel prett}^
confident that those readers are not themselves
working physiologists, and, therefore, that they are
reall}^ ignorant of the time and labovu' required to
devuse and execute even apparently simple experi-
ments, to hunt down a physiological question to
its only possible answer, and to verify each step in
the process of an experimental proof. Moreover,
the difficulties in all these respects are increased
tenfold in a seaside laboratory without adequate
equipments or attendance, and where, in conse-
quence, more time is usually lost in devising make-
shifts for apparatus, and teaching unskilled hands
how to help, than is consumed in all other parts of
a research. From the picnic point of view, how-
ever, there is no real loss in this; such incidental
difficulties add to the enjoyment (else why choose to

INTRODUCTION. 5

make an extemporized grate and boil a kettle in the
wood, when a much more efficient grate, full of lighted
coals, is already boiling some other kettle at home?);
and if they somewhat unduly prolong a research, the
full meaning of life is, after all, not exhausted by the
experiences of a mill-horse, and it is well to remem-
ber that so soon as we cease to take pleasure in our
work, we are most likely sacrificing one part of our
humanity to the altar of some other, and probably
less worthy, constituent.

I may now say a few words on the scope of the
investigations which are to be described in the
present treatise. To some extent this is conveyed
by the title ; but I may observe that, as the " primi-
tive nervous systems" whose physiology I have
sought to advance are mainly subservient to the
office of locomotion, in my Royal Society papers
upon these researches I have adopted the title of
'' Observations on the Locomotor System " of each
of the classes of animals in question. It is of
interest to notice in this connection that the plan
or mechanism of locomotion is completely different
in the two classes, and that in the case of each class
the plan or mechanism is unique, i.e. is not to be
met with elsewhere in the animal kingdom. It is
curious, however, that, in the case of one family of
star-fish (the Comatulce), owing to an extreme
modification of form and function presented by the
constituent parts of the locomotor organs, the
method of progression has come closely to resemble
that which is characteristic of jelly-fish.

There is still one preliminary topic on which I

6 JELLY-FISH, STAE-FISII, AND SEA-URCHINS.

feel tliat it is dcsivcable to toucli before proceeding
to give au account of my experiments, and this has
reference to the vivisection which many of t])cse
experiments have entailed. But in saying what
I have to say in this connection I can afford to be
brief, inasmuch as it is not needful to discuss tho
so-called vivisection question. I have merely to
make it plain that, so far as the experiments which
I am about to describe are concerned, there is not
an}^ reasonable ground for supposing that pain can
have been suffered by the animals. And this it is
easy to show ; for the animals in question are so low
in the scale of life, that to suppose them capable
of conscious suffering would be in the higliest
degree unreasonable. Thus, for instance, they are
considerably lower in the scale of organization tlian
an oyster, and in none of the experiments which
I have performed upon them has so much laceration
of Jivino' tissue been entailed as that whicli is
caused by opening an oyster and eating it alive,
after due application of pepper and vinegar. There-
fore, if any one should be foolish enough to object
to my experiments on the score of vivisection, a
fortiori they are bound to object to the culinary
use of oysters. Of course, it may be answered to
this that two blacks do not make a white, and that
I have not by this illustration succeeded in proving
my negative. To this, however, I may in turn
reply that, for the purpose of morally justifying my
experiments on the ground which I have adopted,
it is not incumbent on me to prove any negative ;
it is rather for my critics to prove a positive. That

INTRODUCTION. 7

is to say, before convincing me of sin, it must be
shown that there is some reasonable ground for
supposing that a jelly-ti.sh or a star-fish is capable
of feeling pain. I submit that there is no such
ground. Tlie mere fact that the animals are alive
constitutes no sucli ground ; for the insectivorous
plants are also alive, and exhibit even more phy-
siological " sensitiveness " and capability of rapid
response to stimulation than is the case with the
animals which we are about to consider. And if
anyone should go so far as to object to Mr. Darwin's
experiments on these plants on account of its not
being demonstrable that the tissues did not suffer
under his operations, such a person is logically bound
to go still further, and to object on similar grounds
to the horrible cruelty of skinning potatoes and

boilino* them alive.

o «

Thus, before any rational scruples can arise with
regard to the vivisection of a living organism, some
reasonable ground must be shown for supposing
that the organism, besides being living, is also
capable of suffering. But no such reasonable ground
can be shown in the case of these low animals.
We only know of such capability in any case
through the analogy based upon our own experi-
ence, and, if we trust to this analogy, we must con-
clude that the capability in question vanishes long
before we come to animals so low in the scale as
the jelly-fish or star-fish. For within the limits of
our own organism we have direct evidence that
nervous mechanisms, much more highly elaborated
than any of those which we are about to consider,

8 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

are incapable of suffering. Thus, for instance, when
the nervous continuity of the spinal cord is inter-
rupted, so that a stimulus applied to the lower
extremities is unable to pass upwards to the brain,
the feet will be actively drawn away from a source
of irritation without the man being conscious of
any pain ; the loAver nervous centres in the spinal
cord respond to the stimulation, but they do so
without feeling the stimulus. In order to feel
there must be consciousness, and, so far as our
evidence goes, it appears that consciousness only
arises when a nerve-centre attains to some such
degree of complexity and elaboration as are to be
met with in the brain. Whether or not there is
a dawning consciousness in any nerve-centres con-
siderably lower in the scale of nervous evolution,
is a question which we cannot answer; but we
may be quite certain that, if such is the case, the
consciousness which is present must be of a com-
mensurately dim and unsuffering kind. Conse-
quently, even on this positive aspect of the question,
we may be quite sure that by the time we come to
the jelly-fish — where the object of the experiments
in the first instance was to obtain evidence of the
very existence of nerve-tissue — all question of pain
must have vanished. Whatever opinions, therefore,
we may severally entertain on the vexed question
of vivisection as a whole, and with whatever feel-
ings we may regard the " blind Fury " who, in the
person of the modern physiologist, "comes with
the abhorred shears and slits the thin-spun life,"

INTRODUCTION. 9

we should be all agreed that in the case of these
animals the life is so very thin-spun that any
suggestion of abhorrence is on the face of it
absurd.*

* The relfition of consciousness to the elaboration of nerve-
centres throughout the animal kingdom is more fully considered
in my work on "Mental Evolution in Animals" (Kcgan Paul,
Trench & Co. : 1SS3).

CPJ AFTER I.

STRUCTURE OF THE MEDUSA

To give a full account of the morphology, develop-
ment, and classification of the MedusiB would be
both unnecessary for our present purposes and
impracticable within the space which is allotted to
the present work.* But, for the sake of clearness
in what follows, I shall begin by briefly describing
such features in the anatomy of the jelly-fish as
will afterwards be found especially to concern us.

In size, the different species of Medusa? vary
from that of a small pea to that of a large umbrella
having streamers a hundred feet long. The
general form of these animals varies in
different species from that of a thimble
(Fig. 1) to that of a bowl, a parasol, or
a saucer (see figures in subsequent chap-
ters). Or we may say that the form of
the animals always resembles that of
a mushroom, and that the resemblance

* Those who may desire to read an excellent epitome of our
most recent knowledge on these subjects, may refer to Professor
E. Ray Lankestei's article in the '* Encyclopaedia Britauuica " on
'* Hydrozoa," together with Professor Haeckel's Report on the
Medusae of the ChaZlenger Expedition.

STEUCTUrvE OF THE MEDUSA. 11

extends to a tolerably close imitation by different
species of the various forms which are characteristic
of di^^erent species of mushrooms, from the thimble-
like kinds to the saucer-like kinds. Moreover,
this accidental resemblance to a nmshroom is in-
creased by the presence of a central organ, occupy-
ing the position of, and more or less resembling
in form, the stalk of a mushroom. This or£ran is
called the " manubrium," on account of its looking
like the "handle" of an umbrella, and the term
" umbrella " is applied to the other portion of the
animal. The manubrium, like the umbrella, varies
much in size and shape in different species, as a
glance at any figures of these animals will show.
Both the manubrium and umbrella are almost
entirely composed of a thick, transparent, and non-
contractile jelly ; but the whole surface of the
manubrium and the whole concave surface of the
umbrella are overlayed by a thin layer or sheet
of contractile tissue. This tissue constitutes the
earliest appearance in the animal kingdom of true
muscular fibres, and its thickness, Avhich is pretty
uniform, is nowhere greater than tliat of very thin
paper.

The manubrium is the mouth and stomach of the
animal, and at the point where it is attached to or
suspended from the umbrella its central cavity
opens into a tube-system, which radiates through
the lower or concave aspect of the umbrella. This
tube-system, which serves to convey digested ma-
terial and may therefore be regarded as intestinal
in function, presents two different forms in the two

12 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

main groups into which the Medust'B are divided.
In the "naked-eyed" group, the tubes are un-
branched and run in a straight course to the margin
of the umbrella, where they open into a common
circular tube which runs all the way round the
margin (see Figs. 1 and 22). In the " covered-eyed "
group, on the other hand, the tubes are strongly
branched (see Fig. 8), although they likewise all
eventually terminate in a single circular tube. This
circular or marginal tube in both cases communi-
cates by minute apertures with the external medium.

The margin of the umbrella, both in the naked
and covered eyed Medusre, supports a series of con-
tractile tentacles, w^hich vary greatly in size and
number in different species (see Figs. 1 and 8). The
margin also supports another series of bodies which
will presently be found to be of much importance
for us. These are the so-called " marginal bodies,"
w^hich vary in number, size, and structure in
different species. In all the covered- e^^ed species
these marginal bodies occur in the form of little
bags of crystals (therefore they are called " litho-
cysts "), which are protected by curiously formed
"hoods " or " covers " of gelatinous tissue ; and it is
on this account that the group is called " covered-
eyed," in contradistinction to the "naked-eyed,"
where these little hoods or coverings are invariably
absent (compare Fig. 1 with Fig. 22), and the
crystals frequently so. In nearly all cases these
marginal bodies contain more or less brightly
coloured pigments.

The question whether any nervous tissue is

STRUCTURE OF THE MEDUSiE. 18

present in the Medusse is one which has long
occupied tlie more or less arduous labours of many
naturalists. The question attracted so much in-
vestigation on account of its being one of unusual
interest in biology. Nerve-tissue had been clearly
shown to occur in all animals higher in the zoolo-
gical scale than the Medusae, so that it was of much
importance to ascertain whether or not the first
occurrence of this tissue was to be met with in
this class. But, notwithstanding the diligent appli-
cation of so much skilled labour, up to the time
when my own researches began there had been so
little agreement in the results obtained by the
numerous investigators, that Professor Huxley —
himself one of the greatest authorities upon the
group — thus defined the position of the matter in his
" Classification of Animals " (p. 22) : " No nervous
system has yet been discovered in any of these
animals."

The following is a list of the more impor-
tant researches on this topic up to the time
which I have just named : — Ehrenberg, " Die
Acalephen des rothen Meeres und der Organismvs
der Medusen der Ostsee," Berlin, 1836 ; Kolliker,
" Ueber die Randkorper der Quallen, Polypen und
Strahlthiere," Froriep's neue Notizen, bd. xxv.,
1843; Von Beneden, "Memoire sur les Campanu-
laires de la cote d'Ostende," " Memoires de
r Academic de Bruxelles," vol. xvii., 1843; Desor,
"Sur la Generation Medusipare des Polypes
hydraires," "Annales d. Scienc. Natur. ZooL," ser. iii.
t. xii. p. 204 ; Krohn, '' Ueber Podocoryna carnea,"

14 JELLY-FISH, STAR-FISH, AND SEA-UIICHINS.

'• Archiv. f. Naturgesclnclite," 1851, b. i. ; McCrady,
*■' Descriptions of Oceania, etc.," " Proceedings of the
Elliot Society of Natural History," vol. i., 1S59 ;
L. Agassiz, " Contributions to the Acalipha) of
North America," "J^Iemoirs of the American
Academy of Arts and Sciences," vol. iii., 18G0,
vol. iv., 18G2; Leuckart, "Archiv. f. Naturge-
schichte," Jahrg. 38, b. ii., 1872 ; Hensen, " Studien
liber das Gehororgan der Decapoden," " Zeitchr. 1
wiss. ZooL," bd. xiii., 1863 ; Semper, ** Reisebcricht,"
" Zeitschr. f. wiss. ZooL," bd. xiii. vol. xiv. ; Glaus,
*' Bemerknngen iiber Glenophoren nnd Medusen,"
"Zeitschr. f. wiss. ZooL," bd. xiv., 18G4 ; Allman,
"Note on the Structure of Gertain H3^droid
MeduscV "Brit. Assoc. Rep.," 1807; Fritz Muller,
" Polypen und Quallen von S. Gatherina," " Archiv.
f. Naturgesch.," Jahrg. 25, bd. i., 1859; also "Ueber
die Rand-blaschen der Hydroidquallen," " Archiv.
f. Anatomic und Physiologic," 1852 ; Haeckel,
"Beitrage zur Naturgesch. der Hydromedusen,"
1865; Eimer, "Zoologische Untersuchungen," Wurz-
burg, " Verhandlungen der Phys.-med. Gesellschaft,"
N.F. vL bd., 1874^.

The most important of these memoirs for us to
consider are the two last. I shall subsequently
consider the work of Dr. Eimer, which up to this
date was of a purely physiological character. Pro-
fessor Haeckel, who made his microscopical obser-
vations chiefly upon the Geryonidro, desciibed the
nervous elements as forming a continuous circle all
round the margin of the umbrella, following the
course of the radial or nutrient tubes throughout

STRUCTURE OF THE MEDUSA. lo

their entire length, and proceeding also to the ten-
tacles and marginal bodies. At the base of each
tentacle there is a ganglionic swelling, and it is
IVoni these ganglionic swellings that the nerves just
mentioned take their origin. The most conspicuous
of these nerves are those that proceed to the radial
canals and marginal bodies, wdiile the least con-
spicuous are those that proceed to the tentacles.
Cells, as a rule, can only be observed in the gan-
glionic swellings, where they appear as fusiform and
distinctly nucleated bodies of great transparency
and high refractive power. On the other hand, the
nerves that emanate from the ganglia are composed
of a delicate and transparent tissue, in which no
cellular elements can be distinguished, but which is
longitudinally striated in a manner very suggestive
of fibrillation. Treatment with acetic acid, how-
ever, brings out distinct nuclei in the case of the
nerves that are situated in the marc^inal vesicles,
while in those that accompany the radial canals
ganglion-cells are sometimes met with.

A brief sketch of the contents of these and other
memoirs on the histology of the Medusfe is given by
Drs. Hertwig in their more recently published work
on the nervous system and sense-organs of the
Medusae, and these authors point to the important
fact that before the appearance of Haeckel's memoir,
Leuckart was the only observer who spoke for the
fibrillar character of the so-called marojinal rino-
nerve ; so that in Haeckel's researches on Geryonia,
whereby both true ganglion -cells and true nerve-
fibres were first demonstrated as occurring in the

If) JELLY-FISH,

Medus?e, we have a most important step in. the
histology of these animals. Haeckel's results in
these respects have since been confirmed by Clans,
"Grundziige der Zoologie," 1872; Allman, "A
Monograph of the Gymnoblastic or Tabularian
Hydroids," 1871 ; Harting, " Notices Zoologiques,"
Niedlandisches "Archiv. f ZooL," bd. ii., Heft 3,
1873 ; F. E. Schulze, " Ueber den Ban von Syncorzne
Sarsii " ; 0. and R. Hertwig, " Das Nervensystem
und die Sinnesorgane der Medusen."

The last-named monograph is much the most
important that has appeared upon the histology of
the Medusa?. I shall, therefore, give a condensed
epitome of the leading results which it has estab-
lished.

There is so great a difference between the nervous
system of the naked and of the covered eyed
Medusse, that a simultaneous description of the
nervous system in both groups is not by these
authors considered practicable. Beginning, there-
fore, with the naked-eyed division, they describe
the nervous system as here consisting of two parts,
a central and a peripheral. The central part is
localized in the margin of the swimming-bell, and
there forms a " nerve-ring," which is divided by the
insertion of the " veil " * into an upper and a lower
nerve-ring. In many species the upper nerve-ring
is spread out in the form of a flattish layer, which

* This is the name given to a small annular sheet of tissue
which forms a kind of floor to the orifice of the swimming-bell,
through the central opening of which floor the manubrium passes,
The structure is shown in Fig. 1.

STKUCTUHE OF THE MEDUSAE. 17

is somewhat thickened where it is in contact with
the veil. In these species the nerve-ring is only
indistinctly marked off' from the surrounding tissues.
But in other species the crowding together of the
nerve-fibres at the insertion of the veil gives rise to
a considerable concentration of nervous structures ;
while in others, again, this concentration proceeds
to the extent of causing a well-defined swelling of
nervous tissue against the epithelium of the veil
and umbrella. In the Geryonidse this swelling is
still further strengthened by a peculiar modification
of the other tissues in the neighbourhood, which had
been previously described by Professor Haeckel. In
all species the upper nerve-ring lies entirely in the
ectoderm. Its principal mass is composed of nerve-
fibres of wonderful tenuity, among which are to be
found sparsely scattered ganglion-cells. The latter
are for the most part bi-polar, more seldom multi-
polar. The fibres which emanate from them are
very delicate, and, becoming mixed with others, do
not admit of being further traced. Where the
nervous tissue meets the enveloping epithelium it
is connected with the latter from within, but diflTers
widely from it ; for the nerve-cells contain a longi-
tudinally striated cjdindrical or thread-like nucleus
which carries on its peripheral end a delicate hair,
while its central end is prolonged into a fine nerve-
fibre. There are, besides these, two other kinds of
cells which form a transition between the ganglion
and the epithelium cells. The first kind are of a
long and cylindrical form, the free ends of which
reach as far as the upper surface of the epithelium.

18 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

The second kind lie for the most part under the
upper surface. They are of a large size, and pre-
sent, coursing towards the upper surface, a long
continuation, which at its free extremity supports a
hair. In some cases this continuation is smaller,
and stops short before reaching the outer surface.
Drs. Hertwig observe that in these peculiar cells we
have tissue elements which become more and more
like the ordinary ganglion-cells of the nerve-ring
the more that their lona: continuation towards the
surface epithelium is shortened or lost, and these
authors are thus led to conclude that the upper
nerve-ring was originally constituted only by such
prolongations of the epithelium-cells, and that after-
wards these prolongations gradually disappeared,
leaving only their remnants to develop into the
ordinary ganglion-cells already described.

Beneath the upper nerve-ring lies the lower
nerve-ring. It is inserted between the muscle-
tissue of the veil and umbrella, in the midst of
a broad strand wherein muscle-fibres are entirely
absent. It here constitutes a thin though broad
layer which, like the upper nerve-ring, belongs to
the ectoderm. It also consists of the same elements
as the upper nerve-ring, viz. of nerve-fibres and
ganglion-cells. Yet there is so distinct a difference
of character between the elements composing the
two nerve-rings, that even in an isolated portion
it is easy to tell from which ring the portion has
been taken. That is to say, in the lower nerve-
ring there are numerous nerve-fibres of considerable
thickness, which contrast in a striking manner with

STRUCTUKE OF THE MEDUSA. 19

the almost immeasurably slender fibres of the
upper nerve-ring. A second point of difference
consists in the surprising Avcalth of ganglion-cells
in the one ring as compared witli the other. Thus,
on the whole, there is no doubt that the lower
nerve-ring pi-esents a higher grade of structure than
does the upper, as shown not only by the greater
multiplicity of nerve-cells and fibres, but also by
the relation in which these elements stand to the
epithelium. For in the case of the lower nerve-
ring, the presumably primitive connections of the
nervous elements with the epithelium is w^ell-nigh
dissolved — this nerve-ring having thus separated
itself from its parent structure, and formed for
itself an independent layer beneath the epithelium.
The two nerve-rings are separated from one another
by a very thin membrane, which, in some species
at all events, is bored through by strands of nerve-
fibres which serve to connect the two nerve-rings
with one another.

The pei'ipheral nervous system is also situated
in the ectoderm, and springs from the central
nervous system, not by any observable nerve-trunks,
but directly as a nervous plexus composed both of
cells and fibres. Such a nei'vous plexus admits
of being detected in the sub-umbrella of all Medusse,
and in some species may be traced also into the
tentacles. It invariably lies between the layer
of muscle-fibre and that of the epithelium. The
processes of neighbouring ganglion-cells in the
plexus either coalesce or dwindle in their course
to small fibres : at the marmn of the umbrella these

20 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

unite themselves with the elements of the nerve-
lings. There are also described several peculiar
tissue elements, such as, in the umbrella, nerve-
fibiX3S which probably stand in connection with
epithelium-cells ; nerve-cells which pass into muscle-
fibres, similar to those which Kleinenberg has
called neuro-muscular cells ; and, in the tentacles,
neuro-muscular cells joined with cells of special
sensation (Sinneszellen).

No nervous elements could be detected in the
convex surface of the umbrella, and it is doubtful
whether they occur in the veil.

In some species the nerve-fibres become aggre-
gated in the region of the generative organs, and
in that of the radial canals, thus giving rise in these
localities to what may be called nerve-trunks. But
in other species no such aggregations are apparent,
the nervous plexus spreading out in the form of an
even trellis-work.

In the covered- eyed MedusiB the central nervous
system consists of a series of separate centres which
are not connected by any commissures. These
nerve-centres are situated in the margin of the
umbrella, and are generally eight in number, more
rarely twelve, and in some species sixteen. They
are thickenings of the ectoderm, which either
enclose the bases of the sense-organs, or only cover
the ventral side of the same. Histologically they
consist of cells of special sensation, together with
a thick layer of slender nerve-fibres. Ganglion-
cells, however, are absent, so that the nerve-fibres
are merely processes of epithelium- cells.

STRUCTUKE OF THE MEDUS.E. 21

Drs. Hertwig made no observations on the peri-
pheral nervous system of the covered-eyed Meckisse ;
but they do not doubt that such a system would
admit of being demonstrated, and intliis connection
they cite the observations of Claus, who describes
numerous ganglion-cells as occurring in the sub-
umbrella of Chrysaora. Here I may appropriately
state that before Drs. Hertwig had published their
results, Professor Schiifer, F.R.S., conducted in my
laborator}^ a careful research upon the histology
of tlie Medusae, and succeeded in showing an
intricate plexus of cells and fibres overspreading
the sub-umbrella tissue of another covered-eyed
Medusa (Aurelia aurita).* He also found that
the marginal bodies present a peculiar modification
of epithelium tissue, which is on its Avay, so to
speak, towards becoming fully diff'erentiated into
ganglionic cells.

Lastly, returning to the researches of Drs. Hert-
wig, these authors compare the nervous system
of the naked-eyed with that of the covered-eyed
Medusce, with the view of indicating the points
which show the latter to be less developed than
the former. These points are, that in the nerve-
centres of the covered-eyed Medusae there are no
true ganglion-cells, or only very few ; that the
mass of the central nervous system is very small;
and that the centralization of the nervous system
is less complete in the one group than in the other.
In their memoir these authors further supply much

* See " Observations on the Nervous System of Aurelia aurita,"
Fhil. Trans., pt. ii., 1878.
3

22 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

interesting information toucliing tlie structure of
the sense-organs in various species of Medusae ;
but it seems scarcely necessary to extend the
j)resent resume of their work by entering into this
division of their subject.

In a later publication, entitled " Der Organismus
der Medusen und seine Stellung zur Keimbliitter-
theorie," Drs. Hertwig treat of sundry features in
the morphology of the Medusae which are of great
theoretical importance ; but here again it would
unduly extend the limits of the present treatise if
I were to include all the ground which has been
so ably cultivated by these industrious workei's.

It will presently be seen in how striking a
manner all the microscopical observations to which
I have now briefly alluded are confirmed by the
physiological observations — or, more correctly, I
might say that the microscopical observations, in so
far as they were concerned with demonstrating the
existence of nerve-tissue in the Medusae, were fore-
stalled by these physiological experiments ; for, with
the exception of Professor Haeckel's work on
Geryonidtie, they were all of later publication. But
in matters of scientific inquiry mere priority is not of
so much importance as it is too often supposed to be.
Thus, in the present instance, no one of the workers
was in any way assisted by the publications of
another. In each case the work was independent
and almost simultaneous.

The remark just made applies also to the only
research which still remains to be mentioned. This
is the investigation undertaken and published by

STRUCTURE OF THE MEDUSA. 28

Professor Eimer.* He began, like myself, by what
in the next chapter I call the " fundamental obser-
vation " on the effects of excising the nerve-
centres, and from this basis he worked both at the
physiology and the morphology of the neuro-
muscular tissues. In point of time, I was the first
to make the fundamental observation, and he was
the first to publish it. The sundry features in which
our subsequent investigations agreed, and those in
which they differed, I shall mention throughout the
course of the following pages.

I shall now conclude this chapter by giving a
brief account of those general principles of tlie
physiology of nerve and muscle with which it is
necessary to be fully acquainted, in order to under-
stand the course of the following experiments.

Nerve-tissue, then, universally consists of two
elementary structures, viz. very minute nerve-cells
and very minute nerve-fibres. The fibres proceed
to and from the cells, so in some cases serving to
unite the cells with one another, and in other cases
with distant parts of the animal body. Nerve-cells
are usually found collected together in aggregates,
which are called nerve-centres or ganglia, to and
from which large bundles cf nerve-fibres come
and go.

To explain the function of nerve- tissue, it is
necessary to begin by explaining what physiologists
mean by the term " excitability." Suppose that a

* " Die Medusen physiologisch und morphologisch auf il.r
NerveuBvstem untersucht " (Tixbingen, 1878).

24 JELLY-FISn, STAR-FISn, AND SEA.-URCHINS.

muscle has been cut from the body of a freshly
killed animal ; so long as it is not interfered with in
any way, so long will it remain quite passive. But
every time a stimulus is supplied to it, either by
means of a pinch, a burn, an electrical shock, or a
chemical irritant, the muscle will give a single
contraction in response to every stimulation. And
it is this readiness of organic tissues to respond to a
suitable stimulus that physiologists designate by
the term " excitability."

Nerves, no less than muscles, present the pro-
perty of being excitable. If, together with the
excised muscle, there had been removed from the
animal's body an attached nerve, every time any
part of this nerve is stimulated the attached muscle
will contract as before. But it must be carefully
observed that there is this great difference between
these two cases of response on the part of the
muscle — that while in the former case the muscle
responded to a stimulus applied directly to its own
substance, in the latter case the muscle responded to
a stimulus applied at a distance from its own
substance, which stimulus was then conducted to the
muscle by the nerve. And in this we perceive the
characteristic function of nerve-^fer^s, viz. that of
conducting stimuli to a distance. The function of
nerve-ce^^s is different, viz. that of accumulating
nervous energy, and, at fitting times, of discharging
this energy into the attached nerve-fibres. The
nervous energy, when thus discharged, acts as a
stimulus to the nerve-fibre ; so that if a muscle is
attached to the end of a fibre, it contracts on receiv-

STRUCTURE OF THE MEDUSAE. 25

ing this stiiniilns. I may add that when nerve-cells
are collected into ganglia, they often appear to
discharge their energy spontaneously ; so that in
all but the very lowest ^nimals, whenever we see
apparently spontaneous action, we infer that ganglia
are probably present. Lastly, another important
distinction must be borne in mind — the distinction,
namely, which is to be drawn between muscle and
nerve. A stimulus applied to a nerveless muscle
can only course through the muscle by giving rise
to a visible wave of contraction, which spreads in
all directions from the seat of disturbance as from a
centre. A nerve, on the other hand, conducts the
stimulus without sensibly moving or undergoing
any change of shape. Now, in order not to forget
this distinction, I shall always speak of muscle-
fibres as conveying a visible wave of contraction,
and of nerve- fibres as conveying an invisible, or
molecular, wave of stinadation. Nerve-fibres, then,
are functionally distinguished from muscle-fibres —
and also from protoplasm — by displaying the pro-
perty of conducting invisible, or molecular, waves
of stimulation from one part of an organism to
another, so establishing physiological continuity
between such parts, without the necessary passage of
waves of contraction.

CHAPTER II.

FUNDAMENTAL EXPERIMENTS.

The naked-eyed Medusse are very much smaller in
size than the covered-eyed, and as we shall find
that the distribution of their nervous elements is
somewhat different, it will be convenient to use
different names for the large umbrella-shaped part
of a covered-eyed Medusa, and the much smaller
though corresponding part of a naked-eyed Medusa.
The former, therefore, I shall call the umbrella, and
the latter the swimming-bell, or nectocalyx. In
each case alike this portion of the animal performs
the office of locomotion, and it does so in the same
way. I have already said that this mushroom-like
organ, which constitutes the main bulk of the
animal, is itself mainly constituted of thick trans-
parent and non-contractile jelly, but that the whole
of its concave surface is lined with a thin sheet of
muscular tissue. Such being the structure of the
organ, the mechanism w^hereby it effects locomotion
is very simple, consisting merely of an alternate
contraction and relaxation of the entire muscular
sheet which lines the cavity of the bell. At each
contraction of this muscular sheet the gelatinous

FUNDAMENTAL EXPERIMENTS. 27

walls of the bell are drawn together ; the capacity
of the bell being thus diminished, water is ejected
from the open mouth of the bell backwards, and the
consequent reaction propels the animal forwards.
In these swimming movements, systole and diastole
follow one another with as perfect a rhythm as
they do in the beating of a heart.

Effects of excising the entire Margins of Nectocalyces.

Confining our attention under this heading to
the naked-eyed Medusae, 1 find that the following
proposition applies to every species of the group
which I have as yet had the opportunity of ex-
amining : Excision of the extreme margin of a
nectocalyx causes immediate, total, and jyermanent
'paralysis of the entire organ. Nothing can possibly
be more definite than in this highly remarkable
efi'ect. I have made hundreds of observations upon
various species of the naked-eyed Medusae, of all
ages and conditions of freshness, vigour, etc. ; and I
have constantly found that if the experiment be
made with ordinary care, so as to avoid certain
sources of error presently to be named, the result is
as striking and decided as it is possible to desire.*
Indeed, I do not know of any case in the animal
kingdom where the removal of a centre of spon-
taneity causes so sudden and so complete a paralysis

* I have only met with one individual exception. This occurred
in a specimen of Staurophora laciniata, where, after removal of
the entire margin, three centres of spontaneity were found to
i-emain in the sheet of contractile tissue lining the nectocalyx.

28 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

of the muscular system, there being no subsequent
movements or twitchings of a reflex kind to disturb
the absolute quiescence of the mutilated organism.
The experiment is particularly beautiful if per-
formed on Sarsia; for the members of this genus
being remarkably active, the death-like stillness
which results from the loss of so minute a portion
of their substance is rendered by contrast the more
surprising.

From this experiment, therefore, I conclude that
in the margin of all the species of naked-eyed
Medusae which I have as yet had the opportunity
of examining, there is situated an intensely localized
system of centres of spontaneity, having at least for
one of its functions the origination of impulses, to
which the contractions of the nectocalyx, under
ordinary circumstances, are exclusively due. And
this obvious deduction is confirmed (if it can be
conceived to require confirmation) by the behaviour
of the sevej-ed margin. This continues its rhyth-
mical contractions with a vigour and a pertinacity
not in the least impaired by its severance from the
main organism, so that the contrast between the
perfectly motionless swimming-bell and the active
contractions of the thread-like portion which has
just been removed from its margin is as striking a
contrast as it is possible to conceive. Hence it is
not surprising that if the margin be left in situ,
while other portions of the swimming-bell are
mutilated to any extent, the spontaneity of the
animal is not at all interfered with. For instance,
if the equator of any individual belonging to the

FUNDAMENTAL EXPERIMENTS. 29

genus Sarsia (Fig. 1) be cut completely through, so
that the swimming-bell instead of being closed at
the top is converted into an open tube, this open
tube continues its rhythmical contractions for an
indefinitely long time, notwithstanding that the
organism so mutilated is, of course, unable to pro-
gress. Thus it is a matter of no consequence how
small or how large a portion of contractile tissue is
left adhering to the severed margin of the swim-
ming-bell ; for whether this portion be large or
small, the locomotor centres contained in the
margin are alike sufficient to supply the stimulus
to contraction. Indeed, if only the tiniest piece of
contractile tissue be left adhering to a single mar-
ginal body cut out of the bell of Sarsia, this tiny
piece of tissue, in this isolated state, will continue
its contractions for hours, or even for days.

Effects of excising the entire Margins of Umbrellas.

Turning now to the covered-eyed division of the
Medusie, I find, in all th^ species I have come across,
that excision of the margins of umbrellas produces
an effect analogous to that which is produced by
excision of the margins of swimming-bells. There
is an important difference, however, between the
two cases, in that the paralyzing effect of the opera-
tion on umbiellas is neither so certain nor so com-
plete as it is on swimming-bells. That is to say,
although in the majority of experiments such
mutilation of umbrellas is followed by immediate
paralysis, this is not invariably the case; so that

so JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

one cannot here, as with the naked-eyed Medusae,
predict with any great confidence what will be the
immediate result of any particular experiment.
Further, although such mutilation of an umbrella is
usually followed by a paralysis as sudden and
marked as that which follows such mutilation of a
swimming-bell, the paralysis of the former differs
from the paralysis of the latter, in that it is very
seldom permanent. After periods varying from a
few seconds to half an hour or more, occasional
weak and unrhythmical contractions begin to mani-
fest themselves, or the contractions may even be
resumed with but little apparent change in their
character and frequency. The condition of the
animal before the operation, as to general vigour,
etc., appears to be one factor in determining the
effect of the operation ; but this is very far from
being the only factor.

Upon the whole, then, although in the species of
covered-eyed Medusiie which I have as yet had the
opportunity of examining, the effects which result
from excising the margins of umbrellas are such as
to warrant nie in saying that the main supply of
locomotor centres appears to be usually situated in
that part of these organs, these effects are neverthe-
less such as to compel me at the same time to con-
clude that the locomotor centres of the covered-eyed
Medusc© are more diffused or seo'rea^ated than are
those of the naked-eyed Medusse. Lastly, it should
be stated that all the species of covered-eyed
MedustB resemble all the species of naked-eyed
Medusse, in that their members will endure any

FUNDAMENTAL EXPERIMENTS. 31

amount of section it is possible to make upon any
of their parts other than their margins without
their spontaneity being in the smallest degree
affected.

Effects of excising Certain Portions of the Margins

of Nectocalyces.

The next question which naturally presents itself
is as to whether the locomotor centres are equally
distributed all round the margin of a swimming
organ, or situated only, or chiefly, in the so-called
marofinal bodies. To take the case of the naked-
eyed Medusae first, it is evident that in most of the
genera, in consequence of the intertentacular spaces
being so small, it is impossible to cut out the
marginal bodies (which are situated at the bases of
the tentacles) without at the same time cutting out
the intervening portions of the margin. The genus
Sarsia, however, is admirably adapted (as a glance
at Fig. 1 will show) for trying the effects of remov-
ing the marginal bodies without injuring the rest
of the margin, and vice versa. The results of such
experiments upon members of this genus are as
follow.

Whatever be the condition of the individual
operated upon as to freshness, vigour, etc., it endures
excision of three of its marginal bodies without
suffering any apparent detriment; but in most
cases, as soon as the last marginal body is cut out,
the animal falls to the bottom of the water quite
motionless. If the subject of the experiment

.32 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

happens to be a weakly specimen, it will, perhaps,
never move again : it has been killed by something
very much resembling nervous shock. On the other
hand, if the specimen operated upon be one which
is in a fresh and vigorous state, its period of
quiescence will probably be but short ; the nervous
shock, if we may so term it, although evidently
considerable at the time, soon passes away, and the
animal resumes its motions as before. In the great
majority of cases, however, the activity of these
motions is conspicuously diminished.

The effect of excising all the marginal tissue from
between the maro-inal bodies and leavinoj the latter
untouched, is not so definite as is the effect of the
converse experiment just described. Moreover,
allowance must here be made for the fact that in
this experiment the principal portion of the " veil" *
is of necessity removed, so that it becomes impos-
sible to decide how much of the enfeebling effect of
the section is due to the removal of locomotor
centres from the swimming-bell, and how much to
a change in the merely mechanical conditions of the
oro-an. From the fact, however, that excision of the
entire margin of Sarsia produces total paralj^sis,
while excision of the marginal bodies alone produces
merely partial paralysis, there can be no doubt that
both causes are combined. Indeed, it has been a
matter of the greatest surprise to me how very
minute a portion of the intertentacular marginal
tissue is sufficient, in case of this genus, to animate
the entire swimming-bell. Choosing

* See Fiff. 1.

FUNDAMENTAL EXPERIMENTS. 83

specimens of Sarsia, I have tried, by cutting out
all the margin besides, to ascertain how minute a
portion of intertentacular tissue is sufficient to
perform this function, and I find that this portion
may be so small as to be quite invisible without the
aid of a lens.

From numerous observations, then, upon Sarsia,
I conclude that in this genus (and so, from analogy,
\ robably in all the other genera of the true
Medus[t3) locomotor centres are situated in every
part of the extreme margin of a nectocalyx, but that
there is a greater supply of such centres in the
marginal bodies than elsewhere.

Effects of excising Certain Portions of the Margin
of Umhrellas.
Coming now to the covered-eyed Medusae, I find
that the concentration of the locomotor centres of
the margin into the marginal bodies, or lithocysts,
is still more decided than it is in the case of Sarsia.
Taking Aurelia aurita as a type of the group, I
cannot say that, either by excising the lithocysts
alone or by leaving the lithocysts in situ and
excising all the rest of the marginal tissue, T have
ever detected the slightest indications of locomotor
centres being present in any part of the margin of
the umbrella other than the eight lithocysts ; so
that all the remarks previously made upon this
species, while we were dealing with the effects of
excising the entire margin of umbrellas, are equally
applicable to the experiment we are now consider-
ing, viz. that of excising the lithocysts alone. In

34 JELLY-FISH, STJLB-FISH, JLN'D SEA-UBCHIXS.

other words, but for the sake of symmetry, I might
as well have stated at the first that in the case of
the oovered-eyed Medusae all the remarkable para-
Ivzintr effects which are obtaine<l hv excising the
entire margin of an umbrella are obtained in exactly
the same degree by excising the eight lithocysts
alone ; the intermediate marginal tissue, in the case
of these Medusse, is totally destitute; of locomotor
centres.

Eg^tds upon the Manuhrium of exci^irig the 3Iarjin
of a Isedocalyx or UmhreUa.

Lastly, it must now be stated, and always borne
in mind, that neither in the case of naked nor
covere<l eyed Medusae does excision of the margin of
a swimming organ produce the smallest effect upon
the manubrium. For hours and days after the
former, in coni^equence of this operation, has ceased
to move, the latter continues to perform whatever
movements are characteristic of it in the unmuti-
lated orc^anism — indeed, these movements are not
at all interfered with even by a complete severance
of the manubrium from the rest of the animal In
many of the experiments subse(juently to be
detailed, therefore, I began by removing the manu-
brium, in order to afford better facilities for
manipulation,

SvLmraary of Cttapier.

With a single exception to hundreds of observa-
tions upon six widely divergent genera of naked-

FUNDAMENTAL EXPERIMENTS. 35

eyed Medusci3, I Hn<l it to be uniformly true that
removal of the extreme periphery of the animal
causes instantaneous, complete, and permanent
paralysis of the locomotor system. In the genus
Sarsia, ray observati'ms point very decidedly to
the conclusion that the principal locomotor centres
are the marginal bodies, but that, nevertheless,
every microscopical portion of the intertentacular
spaces of the margin is likewise endowed with
the property of originating locomotor impulses.

In the covered-eyed division of the Medusie, I find
that the principal seat of spontaneity is the
margin, but that the latter is not, as in the naked-
eyed Medusae, the exclusive seat of spontaneity.
Although in the vast majority of cases I have found
that excision of the margin impairs or destroys the
spontaneity of the animal for a time, I have also
found that the paralysis so produced is very seldom
of a permanent nature. After a variable period
occasional contractions are usually given, or, in
some cases, the contractions may be resumed with
but little apparent detriment. Considerable differ-
ences, however, in these respects are manifested by
different species, and also by different individuals
of the same species. Hence, in comparing the
covered-eyed group as a wdiole with the naked-eyed
group as a whole, so far as my observations extend,
I should say that the former resembles the latter in
that its representatives usually have their main
supply of locomotor centres situated in their
margins, but that it differs from the latter in that
its representatives usually have a greater or less

of) JELLY-FISH, STAR-FISH, AND SEA-URCHINS,

supply of their locomotor centres scattered through
the pfeneral contractile tissue of their swimniino-
oro-ans. But althousfh the kicomotor centres of a
covered-eyed Medusa are thus, generally speaking,
more diffused than are those of a naked-eyed
Medusa, if we consider the organism as a whole,
the locomotor centres in the margin of a covered-
eyed Medusa are less diffused than are those in the
margin of a naked-eyed Medusa. In no case does
the excision of the margin of a swimming organ
produce any effect upon the movements of the
manubrium.

CHArXER III.

EXPERIMENTS IN STIMULATION.

Mechanical, Chemical, and Thermal Stim^ulation.

So far as m}^ observations extend, I find that all
Medusre, after removal of their locomotor centres,
invariably respond to every kind of stimulation.
To take the case of Sarsia as a type, nothing can
possibly be more definite than is the single sharp
contraction of t^e mutilated nectocalyx in response
to every nip with the forceps. The contraction is
precisely similar to the ordinary ones that are per-
formed by the unmutilated animal ; so that by
repeating the stimulus a number of times, the
nectocalyx, with its centres of spontaneity removed,
may be made to progress by a succession of con-
tractions round and round the vessel in which it is
contained, just as a frog, with its cerebral hemi-
spheres removed, may be made to hop along the
table in response to a succession of stimulations.*

* In the case of the covered-eyed Medusas, however, the
paralyzed Timbrella sometimes responds to a single stimtilation
with two, and more rarely with three Contractions, which are
separated from one another by an interval of the same duration
as the normal diastole of the unmutilated animal.
■ 4

33 JELLY-FISH, STAR-FISH, AND SEA-URCHl\-S.

Different species of Medusye exhibit different
degrees of irritability in responding to stimuli ; but
in all the cases I have met with the decree of
irritability is remarkably high. Thus, I have seen
responsive contractions of the whole umbrella follow
upon the exceedingly slight stimulus caused by
a single drop of sea- water let fall upon the irritable
surface from the height of one inch. As regards
chemical stimulation, dilute spirit or other irritant,
when dropped on the paralyzed swimming organ of
Aurelia aurita, often gives rise to a whole series
of rhythmical pulsations, the systoles and diastoles
following one another at about the same rate as is
observable in the normal swimming motions of the
unmutilated animal.

It is somewhat difficult, in the case of paralyzed
swimming organs, to prove the occurrence of a
contraction in respon e to thermal stimulation, from
the fact th.^.t while these tissues are not nearly so
sensitive to this mode of excitation as might be
anticipated, they are, as just observed, extraordi-
narily sensitive to mechanical excitation. It there-
fore becomes difficult to administer the appropriate
thermal stimulus without at the same time causing
a sufficient mechanical disturbance to render it
doubtful to which of the stimuli the resj)onse is
due. This may be done, however, by allowing
a few drops of heated sea- water to run over the
excitable surface while it is exposed to the air. In
this and in other ways I have satisfied myself that
the paralyzed tissues of swimming organs respond
to sudden cl<^^^ations of temperature.

EXPERIMENTS IN STIMULATION, 80

Luminous Sthnulation.

It is interesting to note that, in the case of some
of the naked-eyed Medusiie, the action of light as
a stimulus is most marked and unfailing. In the
case of Sarsia, for instance, a flash of light let fall
upon a living specimen almost invariably causes it
to respond with one or more contractions. If the
animal is vigorous and swimming freely in water,
the effect of a momentary flash thrown upon it
during one of the natural pauses is immediately to
originate a bout of swimming. But if the animal is
non-vigorous, or if it be removed from the water and
spread flat upon an object-glass, it usually gives
only one contraction in response to every flash.
There can thus be no doubt that a sudden transi-
tion from darkness to light acts upon Sarsia as
a stimulus, and this even though the transition be
but of momentary duration. The question there-
fore arises as to whether the stimulus consists in
the presence of light, or in the occurrence of the
sudden transition from darkness to liMit and from
light to darkness. To answer this question, I tried
the converse experiment of placing a vigorous
specimen in sunlight, waiting till the middle of one
of the quiescent stages in the swimming motions
had come on, and then suddenly darkening. In no
case, however, under these circumstances, did I
obtain any response ; so that I cannot doubt it is
the light per se, and not the sudden nature of the
transition from darkness to light, which in the
former experiment acted as the stimulus. Indeed,

40 JELLY-FISH, STAR-FISH, AND SEA-UECHINS.

the effect of the converse experiment just described
is rather that of inhibiting contractions ; for, if the
sunlight be suddenly shut off during the occurrence
of a swimming bout, it frequently happens that the
quiescent stage immediately sets in. Again, in
a general way, it is observable that Sarsise are
more active in the light than they are in the dark,
the comparative duration of the quiescent stages
beino- less in the former than in the latter case.
Light thus appears to act towards these animals as
a constant stimulus. Lastly, it may be stated that
when the marginal bodies of Sarsia are removed,
the swimming-bell, although still able to contract
spontaneously, no longer responds to luminous
stimulation of any kind or degree. But if only one
body be left in ^itu, or if the severed margin alone
be experimented upon, the same unfailing response
may be obtained to luminous stimulation as that
which is obtained from the entire animal.

The fact last mentioned indicates that the mar-
ginal bodies are organs of special sense, adapted to
respond to luminous stimulation ; or, in more simple
words, that they perform the functions of sight.
Now it has long been thought more or less probable
that these marginal bodies are rudimentary or
incipient " eyes," but hitherto the supposition has
not been tested by experiment, and was therefore of
no more value than a guess.* The guess in this

* As Professor Haeckel observes in his monofj^raph already
alluded to, '"Die Deutung der Sinnesorgane niederer Thiere
geliort ohne Zweifel zu den schwierigsten Obiecten der vergleic-
henden Pbysiologie nnd ist der grossten Unsicherbeit nnterworfen.
VVir Bind gewolint, die von den Wirbeltbieren gcwonnenen

EXPEIUMENTS IN STIMULATION. 41

instance, however, happens to have been correct, as
he results of the following experiments will show.

Having put two or three hundred Sarsifle into a
large bell-jar, I completely shut out the daylight
from the room in which the jar was placed. By
means of a dark lantern and a concentrating lens,
I then cast a beam of light through the water in
which the SarsijB were swimming. The effect upon
the latter was most decided. From all parts of the
bell-jar they crowded into the path of the beam,
and were most numerous at that side of the jar
which was nearest to the light. Indeed, close
against the glass they formed an almost solid mass,
which followed the light wherever it was moved.
The individuals composing this mass dashed them-
selves against the glass nearest the light with a
vigour and determination closely resembling the
behaviour of moths under similar circumstances.
There can thus be no doubt about Sarsia possessing
a visual sense.

Anschauungen oline Weiteres auch auf die wirbellosen Thiere der
verscliiedenen Kirese zu iibertragea und bei diesen analoge
Sinnesempfindungen anzunehmen als wir sebst besitzen. . .
Noch weniger freilich als die von den meisten Autoren angenom-
mene Deutung der Randblaschen nnserer Medusen als Gehororgane
kann die von Agassiz und Fritz Miiller vertretene Ansicht befrie-
digen, dass dieselben Augen seien. . . . Alle diese Verhaltnisse
sind mit der Deutung der Concretion als 'Linse' und des sie
umschliessenden Sinnesganglion als ' Sehnerv * durchaus nnve-
reinbar."

It may not be unnecessary to say that, although the simple
experiment above described effectually proves that the marginal
bodies have a visual function to subserve, we are not for this
reason justified in concluding that these are so far specialized as
organs of sight as to be precluded from ministering to any other

42 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

The method of ascertaining whether this sense
is lodged in the marginal bodies was, of course,
extremely simple. Choosing a dozen of the most
vigorous specimens, I removed all the marginal
bodies from nine, and placed these, together with
the three unmutilated ones, in another bell-jar.
After a few minutes the mutilated animals recovered
ii'om their nervous shock, and began to swim about
with toleiable vigour. I now darkened the room,
and threw the concentrated beam of light into the
water as before. The difference in the behaviour
of the mutilated and of the unmutilated specimens
was very marked. The three individuals which
still had their marginal bodies sought the light as
before, while the nine without their marginal bodies
swam hither and thither, without paying it any
I'egard.

A further question, however, still remained to be
determined. The pigment spot of the marginal
body in Medusae is, as L. Agassiz observed, placed in
front of the presumably nervous tissue, and for
this reason he naturally enough suggested that if
the marginal body has a visual function to perform,
the probability is that the rays by which the organ
is affected are the heat- rays lying beyond the range
of the visible spectrum. Accordingly I brought a
heated iron, just ceasing to be red, close against the
large bell-jar which contained the numerous speci-
mens of Sarsia ; but not one of the latter approached
the heated metal.

From these observations, therefore, I conclude
that in Sarsia the faculty of appreciating luminous

EXPERIMENTS IN STIMULATION. 4o

rays is present, and that this faculty is lodged
exclusively in the marginal bodies; while from
observations conducted on the covered-eyed Medusa,
I have come to the same conclusion respecting them.
But although I have tested many species of naked-
eyed Medusie besides Sarsia, I have obtained indi-
cations of response to luminous stimulation only
in the case of one other. This is a species which
I have called Tiaropsis polydiademata, and the
response which it gives to luminous stimulation
is even more marked and decided than that which
is given by Sarsia ; for a sudden exposure to sun-
light causes this animal to go into a kind of tonic
spasm, the whole of the nectocalyx being drawn
together in a manner resembling cramp. Now, in
one remarkable particular tliis response to luminous
stimulation on the part of Tiaropsis polydiademata
differs from that given by Sarsia tubulosa ; and
the difference consists in the fact that, while with
Sarsia the period of latency (i.e. the time between
the fall of the stimulus and the occurrence of the
response) is, so far as the eye can judge, as instan-
taneous in the case of response to luminous stimu-
lation as it is in the case of response to any other
kind of stimulation, such is far from beino- true
with Tiaropsis polydiademata. The period of
latency in the last-named species is, so far as the
eye can judge, quite as instantaneous as it is in
the case of Sarsia, when the stimulus employed is
other than luminous ; but in response to light, the
characteristic spasm does not take place till slightly
more than a second has elapsed after the first

44 JELLY-FISH, STAR-FISH, AND SEA-URCIIIXS.

occurrence of the stimulus. As this extraordinary
difference in the latent period exhibited by the
same animal towards different kinds of stimuli
appeared to me a matter of considerable interest,
I was led to reflect upon the probable cause of the
difference. It occurred to me that the only respect
in which luminous stimulation of the Medusai
differed from all the other modes of stimulation I
had employed consisted in this — that, as proved by
my previous experiments on Sarsia, which I repeated
on Tiaropsis, luminous stimulation directly aflected
the ganglionic tissues. Now, as in Tiaropsis poly-
diademata luminous stimulation differed from all
the other modes of stimulation in giving rise to an
immensely longer period of latency, I seemed here
to have an index of the difference between the
rapidity of the response to stimuli by the contractile
and by the ganglionic tissues respectively. The
next question, therefore, which presented itself was
as to whether the enormous length of time occupied
by the process of stimulation in the ganglia w^as
due to any necessity on the part of the latter to
accumulate the stimulating influence prior to origi-
nating a discharge, or to an immensely lengthened
period of latent stimulation manifested by the
ganglia under the influence of light.* This is an

* The period of latent stimulation merely means the time after
the occurrence of an excitation duiing which a series of physiolo-
gical processes are taking place, which terminate in a contrac-
tion ; so that, whether the excitation is of a strong or of a weak
intensity, the period of latent stimulation is not much affected.
The above question, therefore, was simply this — Does the pro-
longed delay on the part of these ganglia, in responding to light,

EXPERIMENTS IN STIMULATION. 45

interesting question, because if such a lengthened
period of latent stimulation occurs in this case, it
would stand in curious antithesis to the very short
period of latent stimulation manifested by the con-
tractile tissues of the same animal under other
modes of irritation. To test these alternative hypo-
theses, I employed the very simple method of first
allowing a continuous flood of light to fall suddenly
on the Medusa, and then noting the time at which
the responsive spasm first bi'gan. This time, as
already stated, was slightty more than one second.
I next allowed the animal to remain for a few
minutes in the dark to recover shock, and, lastly,
proceeded to throw in single flashes of light of
measured duration. I found that unless the flash
of light was of slightly more than one second in
its duration, no response was given ; that is to
say, the minimal duration of a flash required to
produce a responsive spasm was just the same as
the time durino^ which a continuous flood of lioht
required to operate in order to produce a similar
spasm. From this, therefore, I conclude that the
enormously long period of latent excitation in
response to luminous stimuli was not, properly
speaking, a period of latent excitation at all ; but
that it represented the time during which a certain
summation of stimulating influence was taking
place in the ganglia, which required somewhat more

represent the time during which the series of physiological pro-
cesses are taking place in response to an adequate stimulus, or
does it rejiresent tlie time during which light requires to act
before it becomes an adequate stimulaa ?

46 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

than a second to accumulate, and which then caused
the ganglia to originate an abnormally powerful
discharge. So that in the action of light upon the
o'anMionic matter of this Medusa we have some
analogy to its action on certain chemical compounds
in this respect, that, just as in the case of those
compounds which light is able to split up, a more
or less lengthened exposure to its intluence is
necessary in order to admit of the sum mating
influence of its vibrations on the molecules, so in
the case of this ganglionic material, the decom-
position which is effected in it by light, and which
terminates in an explosion of nervous energy, can
only be effected by a prolonged exposure of the
unstable material to the summating influence of
the luminous vibrations. Probably, therefore, we
have here the most rudimentary type of a visual
organ that is possible ; for it is evident that if tlie
ganglionic matter were a very little more stable
than it is, it would altogether fail to be thrown
down by the luminous vibrations, or would occupy
so long a time in the process that the visual sense
would be of no use to its possessor. How great is
the contrast between the excitability of such a
sense-organ and that of a fully evolved eye, which
is able to efTect the needful molecular changes in
response to a flash as instantaneous as that of
lightning.

With regard to luminous stimulation, it is only
necessary further to observe that responses were
given equally well to direct sunlight, diffused day-
liglit, and to light reflected from a mirror inclined

EXPERIMENTS IN STIMULATION. 47

at the polarizing angle. It must also be stated that
responses are given to any of the luminous rays of
the spectrum when these are employed separately;
but that neither the non-luminous rays beyond
the red, nor those beyond the violet, appear to exert
the smallest degree of stimulating influence.

Electrical Stimulation.

All the excitable parts of all the Medusae which I
have examined are highly sensitive to electrical
stimulation, both of the constant and of the induced
current.

Exploration with needle-point terminals and in-
duction shocks of graduated strength showed that
certain parts or tracts of the nectocalyx are more
sensitive than others. The most sensitive parts are
those which correspond with the distribution of the
main nerve-trunks, i.e. round the margin of the
nectocalyx and along the course of the radial tubes.
The external or convex surface of a nectocalyx or
umbrella is totally insensitive to stimulation, and
the same statement applies to the whole thickness
of the gelatinous substance to which the neuro-
muscular sheet is attached.

In all other respects the excitable tissues of the
Medusue in their behaviour towards electrical
stimulation conform to the rules which are followed
by excitable tissues of other animals. Thus, closure
of the constant current acts as a stronger stimulus
than does opening of the same, while the reverse is
true of the induction shock ; and exhaustion super-

48 JELLY-FISH, STAU-FISH, AND SEA-UllCllINS.

venes imdor the inflaence of prolonged excitation.
Moreover, I have obtained evidence of that polariza-
tion of nerve-tissues under the influence of the
constant current, which is known to physiologists
by the term " electrotonus ; " but it would be some-
what tedious to detail the evidence on this head
which I have alread}^ published elsewhere.* Teta-
nus produced by faradaic electricity is not of the
nature of an apparently single and prolonged con-
traction, but that of a number of contractions
rapidly succeeding one another, as in the case of the
heart under similar excitation. This at least applies
to Sarsia. In the case of Aurelia, tolerably strong
faradization does cause a more or less well-pro-
nounced tetanus. The continuity of the spasm is,
indeed, often interrupted by momentary and partial
relaxations. These interruptions are the more fre-
quent the weaker the current ; so that, at a certain
streno-th of the latter, the tetanus is of a wild and
tumultuous nature; but with strong currents the
spasm is tolerably uniform. That in all cases the
tetanus is due to summation of contracticms may
be very prettily shown by the following experi-
ment. An Aurelia is cut into a spiral strip, and all
its lithocysts are removed ; single induction-shocks
are then thrown in with a key at one end of the
strip — every shock, of course, giving rise to a con-
traction wave. If these shocks are thrown in at a
somewhat fast rate, two contraction waves may be
made at the same time to course along the spiral

* See " Croonian Lectures,*' 1875. Philosophical Transactions,
vol. 166, part I. pp. 281-6.

EXPERIMENTS IN STIMULATION. 49

strip, one beliind the other; but if the shocks are
thrown in at a still faster rate, so as to diminish the
distance between any two successive waves, a point
soon arrives at which every wave mounts upon its
predecessor ; and if several waves be thus made to
coalesce, the whole strip becomes thrown into a
state of persistent contraction.

In this way sustained tetanus, or single con-
traction waves, or any intermediate phase, may be
instantly produced at pleasure. In such experi-
ments, moreover, it is interesting to observe that, no
matter how long the strip be, whatever disturbances
are set up at one end are faithfully transmitted to
the other. For instance, if an Aurelia be cut into
the longest possible strip with a remnant of the disk
leff attached at one end, as represented in Fig. 11
(p. 70), then all the peculiar time relations between
successive contractions which are intentionally
caused by the experimenter at one end of the strip,
are afterwards accurately reproduced at the other
end of the strip by the remainder of the disk.
Now, as this fact is observable however complex
these time relations may be, and however rapidly
the successive stimuli are thrown in, I think it is
a point of some interest that these complicated
relations among rapidly succeeding stimuli do not
become blended during their passage along the
thirty or forty inches of contractile tissue. The
fact, of course, shows that the rate of transmission
is so identical in the case of all the stimuli
originated, that the sum of the effects of any series
of stimuli is delivered at the distal end of the strip,

50 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

with all its constituent parts as distinct from one
another as they were at starting from the proximal
end of the strip.

Period of Latency, and Suniraation of Stimuli

I shall now give an account of my experiments
in the period of latency and the summation of
stimuli. To do this, I must first describe the method
which I adopted in order to obtain a graphic record
of the movements which were given in response to
the stimuli supplied. As Aurelia aurita is the only
species on which I have experimented in this con-
nection, my remarks under this heading will be
confined to it alone.

The method by which I determined the latent
period in the case of this species was as follows.
A basin containing the Medusa was filled to its
brim with sea-water, and placed close beside a
smoked cylinder, wdiich, while it lay in a horizontal
position, could be rotated at a known rate. The
Aurelia* was placed with its concave aspect upper-
most, and an inch or two below the surface of the
water. The animal was held firmly in this position
by means of a pair of compasses thrust through it
and forced into a piece of wood, which was fastened
to the bottom of the basin. The legs of the com-

* It may here be stated that in all the experiments on stimu-
lation subsequently to be detailed, there is no difference to be
observed between the behaviour of an entire swimming^ organ
deprived of its ganglia, and that of a portion of an}' size which
may be separated from i- .

EXPERIMENTS IN STIMULATION. 61

passes were provided with india-rubber sliders, so
that by placing these under the Medusa, the latter
might be kept at any elevation in the water which
might be desired. The manubrium and lithocysts
were now removed, and also a segment of the um-
brella. A light straw was then forced through the
gelatinous substance of the umbrella in a radial
direction, and close to the gap caused by the missing
segment. The other, or free, end of this straw was
firmly joined to a capillary glass rod, which was suit-
ably bent to avoid contact with the rim of the basin,
and also to write on the smoked cylinder. If the
straw was not itself sufficient to support the weight
of the capillary rod, a small cross-piece of cork
might easily be tied to it, so as to add to the
flotation power. A part of the excitable tissue
was now raised above the surface of the water by
means of a disk of cork placed beneath it, and on
the part of the tissue thus raised there were placed
a pair of platinum electrodes. These electrodes
proceeded from an electro-magnetic apparatus, which
was arranged in such a way that every time the
current in it was opened or closed, it gave an
induction shock and moved a lever at the same
instant of time. This lever was therefore placed
upon the cylinder immediately above the capillary
glass-writer which proceeded from the Medusa
care being taken to place the two writers in the
same line, parallel to the axis of the cylinder.
Such being the arrangement, the cylinder was
rotated, and thus two parallel lines were marked
upon it by the two writers. If the current was

52 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

now closed, an induction shock Avas thrown into
the tissue at the same instant that the electro-
magnet writer recorded the fact, by altering its
position on the cylinder. Again, as soon as the
paralyzed Medusa responded to the induction shock,
the radii of the vacant segment were drawn apart,
and in this way a curve was obtained by the other
writer on the rotating cylinder. Now, by after-
wards dropping a perpendicular line from the point
at which the electro-magnet writer changed its
position, to the parallel line made by the other
writer, and then measuring the distance between
the point of contact and the point on the last-
mentioned line on which the curve began, the period
of latent stimulation was determined. A glance at
Figs. 3 and 4 (p. 55) will render this description
clear to any one who is not already acquainted with
the method, when it is stated that the upper line
is a record of the movements of the electro- magnet
writer, and the lower line that of the movements of
the other writer. It will be observed that the
point a in the upper line marks the point at which
the induction shock was thrown in ; so that by
first producing the perpendicular till it meets the
lower line at 6, and then measuring the distance
between the point h and the point c, .at which
the curve in the lower line first begins, the latent
period (h c) is determined — the time occupied by
the rotation of the cylinder from 6 to c being
known.

Summation of Stimuli. — In this way I have
been able to ascertain the period of latent stimula-

EXPERIMENTS IN STIMULATION. 53

tlon in Aurelia aurita with accuracy. It must be
stated at the outset, however, that this period is
subject to great variations under certain varying
conditions, so that we can only arrive at a just
estimation of it by understanding the nature of the
modifying causes. To take the simplest cause first,
suppose that the paralyzed Aurelia has been left
quiet for several minutes in sea-w^ater at forty-five
degrees, and that it is then stimulated by means of
a single induction shock ; the responsive contrac-
tion will be comparatively feeble with a very long
period of latency, viz. five-eighths of a second. If
another shock of the same intensity be thrown in
as soon as the tissue has relaxed, a somewhat
stronger contraction, with, a somewhat shorter latent
period, will be given. If the process is again re-
i:>eated, the response will be still more powerful,
with a still shorter period of latency ; and so on,
perhaps, for eight or ten stages, when the maximum
force of contraction of which the tissue is capable
will have been attained, while the period of latency
wdll have been reduced to its minimum. This
period is three-eighths of a second, or, in some
cases, slightly less.

Now, we have here a remarkable series of pheno-
mena, and as it is a series which never fails to occur
under the conditions named, I append tracings to
give a better idea of the very marked and striking
character of the results. The first tracing (Fig. 2)
is a record of the successive increments of the
responses to successive induction shocks of the same
intensity, thrown in at three seconds' intervals —

54 JELLY-FISH, STAR-FISH, AND SKA-URCHINS.

the cylinder being stationary during each response,
and rotated a short distance with the hand during
each interval of repose.

The second tracing (Figs. 3 and 4) is a record of
the difference between the lengths of the latent
period, and also between the strengths of the con-
traction, in the case {a) of the first of such a series
of responses (Fig. 3), and (6) of the last of such a
series (Fig. 4). From these tracings it will be
manifest, without further comment, how surprising
is the effect of a series of stimuli; first, in aroiisliKj
the tissue, as it were, to increased activity, and,
second, in developing a state of expectancy.

In accordance with the now customary termi-
nology, I shall call such a series of responses as are
given in Fig. 2a" staircase." Such a staircase has
a greater number of steps in it if caused by a weak
current (compare Figs. 2 and 5) ; and if the strength
of the current be suddenly increased after the
maximum level of a staircase has been reached by
using a feeble current, this level admits of being
s'ightly raised (see Fig. 5). Moreover, I lind that a

EXPERIMENTS IX SriMTLATIOX. o5

stimulus, ^vhicli at the bottom of a staircase is of
less than minimal intensity, is al)le, at the top of a

staircase, to give rise to a contraction of very nearly
maximum intensity. That is to say, by employing

56 JELLY-FISH, STAR-FLSH, AND SEA-URCHINS.

an induction stimulus of slightly less than minimal
intensity in relation to the original irritability oi

the tissue, no response is given to the first two or
three shocks of a series ; but at the third or fourth
shock a slight response is given, and from that
point onward the staircase is built up as usual.
This was the case in the experiment of which Fig. 2
is a record, no response having been given to the
first two shocks.

With regard to this interesting staircase action,
two questions naturally present themselves. In
the first place, we are anxious to know whether the
arousing effect which is so conspicuous in a stair-
case series is due to the occurrence of the previous
stimulations, or to that of previous contractions;
and, in the next place, we should like to know
whether, during the natural rhythm of the tissue,
each contraction exerts a beneficial influence on its
successor, analogous to that which occurs in the case
of contractions which are due to artijicial stimuli. To

EXPERIMENTS IN STIMULATION. 57

answer the first of these questions, therefore, I built
up a staircase in the ordinary way, and then sud-
denly transferred the electrodes to the opposite side
of the umbrella from that on which they rested while
constructing the staircase. On now throwing in
another shock at this part of the contractile tissue
so remote from the part previously stimulated, the
response was a maximum response. Similarly, if
the electrodes were transferred in the way just
described, not after the maximum effect had been
attained, but at any point during the process of
constructing a staircase, the response given to the
next shock was of an intensity to make it rank as
the next step in the staircase. Hence, shifting the
position of the electrodes in no wise modifies the
peculiar eff'ect we are considering ; and this fact
conclusively proves that the effect is a general one,
pervading the whole mass of the contractile tissue,
and not confined to the locality whicli is the imme-
diate seat of stimulation. Nevertheless, this fact does
not tend to prove that the staircase effect depends
on the process of contraction as distinguished from
the process of stimulation, because the wave of the
former process must always precede that of the
latter. But, on the other hand, in this connection
it is of the first importance to remember the fact
already stated, viz. that a current which at the be-
ginning of a series of stimulations is of slightly less
than minimal intensity presently becomes minimal,
and eventually of much more than minimal in-
tensity— a staircase being thus built up of which
the first observable step (or contraction) only occurs

58 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

in response to the second, tliird, or even fourth
shock of the series. This fact conclusively proves
that the staircase effect, at any rate at its com-
mencement, depends on the process of stimulation
as distinguished from that of contraction ; for it is
obvious that the latter process cannot play any
part in thus constructing what we may term the
invisible steps of a staircase.

To answer the second of the above questions, I
placed an Aurelia with its concave suriace upper-
most, and removed seven of its lithocysts ; I then
observed the spontaneous discharge of the remain-
ing one, and found it to be conspicuous enough that,
after the occurrence of one of the natural pauses (if'
this were of sufficient duration), the first contraction
was feeble, the next stronger, the next still stronger,
and so on, till the maximum was attained. This
natural staircase action admits of being very prettily
shown in another way. If a tolerably large Aurelia
is cut into a spiral strip of small width and great
length, and if all the lithocysts are removed except
one at one end of the strip, it may be observed that,
after the occurrence of a natural pause, the first
discharge only penetrates perhaps about a quarter
of the length of the strip, the next discharge pene-
trates a little further, the next further, and so on,
till finally the contraction waves pass from end to
end. On now removing the ganglion, waiting a
few minutes, and then stimulating with successive
induction shocks, the same progressive penetration
is observable as that which previously took place
with the ganglionic stimulation. Lastly, the

EXPERIMENTS IN STIMULATlOX. 59

identity of natural and artificial staircase action
may be placed beyond all doubt by an experiment
in which the effects of induction shocks and of
ganglionic discharges are combined. To accomplish
this, all the lithoc3^sts save one are removed, and
a staircase is then built up in the ordinary way by
successive induction shocks. It will now occasion-
ally happen that the ganglion originates a discharge
during the process of constructing the staircase,
which is being built up by the artificial stimuli ;
when this happens the resulting contraction takes
its proper rank in the series, and this at whatever
point the natural contraction happens to couie in.

Thus, then, to summarize and conclude these
observations, we have seen that if a single stimula-
tion, whether of a natural or artificial kind, is
supplied to the excitable tissues of a jelly-fish, a
.short period, called the period of latency, will
elapse, and then the jelly-fish will give a single
weak contraction. If, as soon as the tissue has
relaxed, the stimulation is again repeated, the
period of latency will be somewhat shorter, and
will be followed by a somewhat stronger contrac-
tion. Similarly, if the stimulation is repeated a
third time, the period of latency will be still
shorter, and the ensuing contraction still stronger.
And so on up to nine or ten times, w^hen the period
of latency will be reduced to its rninimum, while
the force of the contraction will be raised to its
maximum; so that in the jelly-fish, the effect of a
series of excitations supplied at short intervals from
one another is that of both arousinof the tissue into

GO JELLY-FJSH, STAR-FISH, AND SEA-UHCUINS.

a state of increased activity, and also of producing
in it a state of greater expectancy. We have, more-
over, seen that this effect depends upon the repe-

' tition of the process of stimulation, and not upon
that of the process of contraction.

Now, effects very similar to these have been
found to occur in the case of the excitable plants
by Dr. Burdon- Sanderson ; in the case of the frog's
heart by Dr. Bowditch ; and in the case of reflex
action of the spinal cord by Dr. Stirling. Indeed,
the only difference in this respect between these
four tissues, so widely separated from one another
in the biological scale, consists in the time which
may be allowed to elapse between the occurrence
of the successive stimuli, in order to produce this
so-called summating effect of one stimulus upon
its successor: the memory, so to speak, of the
heart-tissue for the occurrence of a former stimulus
being longer than the memory of the jelly-fish
tissue; while the memory of the latter is longer
than that of the plant tissue. And I may here
add that even in our own organization we may
often observe the action of this principle of the
summation of stimuli. For instance, we can

. tolerate for a time the irritation caused by a crumb
in the larynx, but very rapidly the sense of irrita-
tion accumulates to a point at which it becomes
impossible to avoid coughing. And similarly with
tickling generally, the convulsive reflex movements
to which it gives rise become more and more incon-
t roll able the longer the stimulation is continued,
until they reach a Tnaxim^um point, where, in

EXPERIMENTS IN STIMULATION. CI

persons susceptible to this kind of stimulation, the
muscular action passes completely beyond the power
of the will. Lastly, I may further observe, what
I do not think has ever been observed before, that
even in the domain of psychology the action of this
principle admits of being clearly traced. We find
it, for instance, in the rhythmical waves of emotion
characteristic of grief, and at the other extreme we
find it in the case of the ludicrous. We can endure
for a short time, without giving any visible re-
sponse, the psychological stimulation which is
supplied by a comical spectacle; but if the latter
continues sufficiently long in a sufficiently ludicrous
manner, our appropriate emotion rapidly runs up
to a point at which it becomes uncontrollable, and
we burst into an explosion of ill-timed laughter.
But in this case of psychological tickling, as in the
previous case of physiological tickling, some persons
are much more susceptible than others. ^Neverthe-
less, there can be no doubt that from the excitable
tissues of a plant, through those of a jelly-fish and
a frog, up even to the most complex of our psj^cho-
logical processes, we have in this recently discovered
principle of the summation of stimuli a very
remarkable uniformity of occurrence.

Effects of Temjperatiire on Excitability.

I shall now conclude this chapter with a brief
statement of the effects of temperature on the
excitability of the Medusae ; and before stating my
results, I may observe that in all my experiments
in this connection I changed the temperature of the

62 JELLY-FISH, STAR-FISII, AND SEA-URCHINS.

Medusae by drawing off the water in wliich tliey
floated with a siphon, while at the same time I
substituted w^ater of a different temperature from
that which I thus abstracted. In this way, without
modifying any of the other conditions to which the
animals were exposed, I was able to observe the
efiects of changing the temperature alone.

With regard to the effect of temperature on the
latent period of stimulation, the following table,
setting forth the results of one among several
experiments, explains itself

Period of latent stimulation of the deganglio-
nated tissues of Aurelia aurita as affected by tem-
perature : —

Temperature of water (Fahr.).

70-

35°

20°

Period of latent stimulation.

^ second
^ second
I second
^ second

In the case of each observation, several shocks
were administered before the latent period was
taken, in order to decrease this period to its
TiiinimuTn by the staircase action. When this is
not done, the latent period at 20° may be as long
as 1 J seconds ; but soon after this irritability
disappears.

The extraordinary sluggishness of the latent
period at very low temperatures is fully equalled
by the no less extraordinary sluggishness of the
contraction.

EXl'ElllMKNTS IN STIMULATION.

03

In order to render apparent the degree in which
both these effects are produced, I here append a
pair of tracings which were procured from the same
piece of tissue when exposed to the different tem-
peratures named. (N.B.— The seconds are wrongly

i'iiX. 0.

Fig. 7.

marked in Fig. 7 ; they ought to he the same as in
Fig. 6.)

I may as well state here that in water at all
temperatures, within the limits where responses to
stimuli are given at all, the staircase action admits

64 JELLY-FISH, srAR-ilSH, AND SEA-UllCHINS.

of being equally well produced ; but in order to
procure the Tiiaxiinitm effect for any given tempera-
ture, the rate at which the successive stimuli arc
thrown in must be quicker in warm than in cold
water.

CHAPTER IV.

KXPERIMENTS IN SECTION OF COVEllED-EYED MEDUSA

Amount of Section which the Neiiro-muscular
Tissues of the Medusoe will endure without
suffering Loss of their Physiological Continuity.

The extent to which the neuro-muscular tissues
of the Medusa may be mutilated without under-
going destruction of their physiological continuity is
in the highest degree astonishing. For instance, to
begin with the covered-eyed Medusae, I shall briefly
state three modes of section, the results of which serve
to show in a striking manner the fact in question.

The annexed woodcuts represent the umbrella of
Aurelia aurita, with its manubrium cut off at the
base, and the under or concave surface of the
umbrella exposed to view, shewing in the centre
the ovaries, and radiating from them the branched
system of nutrient tubes. The umbrella when
fully expanded, as here represented, is about the
size of a soup plate, and, as previously stated, all
the marginal ganglia are aggregated in the eight
marginal bodies or lithocysts. Therefore if the
reader will imagine the first of the diagrams (Fig. 8)

no JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

to be overspread with a disc of muslin, the fibres
and mesh of which are finer than those of the finest
and closest cobweb, and if he will imagine the mesh
of these fil)res to s^art from these maroinal oranglia,

he will gain a tolerably correct idea of the lowest
nervous system in the animal kingdom. Now,
suppose that seven of these eight ganglia are cut
out, the remaining one then continues to supply its
rhythmical discharges to the muscular sheet of the

SECTION OF COVERED-EYED MEDUSA.

G7

bell, the result being, at each discharge, two con-
traction waves, which start at the same instant,
one on each side of the ganglion, and which then
course with equal rapidity in op])osite directions,

mm' m

Fig. 9.

and so meet at the point of the disc which is
opposite to the ganglion. Suppose, now, a number
of radial cuts are made in the disc according to
such a plan as this (Fig. 9), wherein every radial
cut deeply overlaps those on either side of it. The

68 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

contraction waves which now originate from the
ganglion must either become blocked and cease to
pass round the disc, or they must zigzag round and
round the tops of these overlapping cuts. Now,
remembering that the passage of these contraction
waves is presumably dependent on the nervous
network progressively distributing the ganglionic
impulse to the muscular fibres, surely we should
expect that two or three overlapping cuts, by
completely severing all the nerve-fibres lying
between them, ought to destroy the functional
continuity of these fibres, and so to block the
passage of the contraction wave. Yet this is not the
case ; for even in a specimen of Aurelia so severely
cut as the one here represented, the contraction
waves, starting from the ganglion, continued to
zigfzao- round and round the entire series of sections.
The second mode of section to which I have
alluded is as follows (Fig. 10). The central circle {x)
stands for an open space cut out of the umbrella ;
the outer circle indicates the margin of the animal,
with all lithocysts save one (I) removed ; and the
median circular line represents a cut. It will be
seen that the effect of this cut is almost completely
to sever the mass of tissue at z from the rest of the
umbrella, the only connection between them being
the narrow neck of tissue at z. Yet, in the case
to which I refer, the contraction waves emanating
from I passed in the directions represented by the
arrows without undergoing any appreciable loss of
vigour. Upon completing the circular cut at z, the
ring of tissue (y z) became totally paralyzed, while

SECTION OF COVERED-EYED MEDUSA.

69

the outer circle, of course, continued its contractions
as before. Now, the neck of tissue at z measured
only one-eighth of an inch across, while the ring of
tissue {y z), when cut through and straightened °out

Fig. 10.

upon the table, measured one inch across and sixteen
inches in length ; that is to say, sixteen square inches
of tissue derived its impulse to vigorous contrac-
tions through a channel one-eighth of an inch wide.

70 JELLY-FISH, STAR-FISH, Ax\D

SEA- URCHINS.

notwithstanding that the latter was situated at the
furthest point of the circle from the discharging

^miMwmmw ^m^^^

Fig. 11.

lithocyst which the form of the section rendered
possible.

SECTION OF COVERED-EYED MEDUSA 71

Lastly, the third mode of section is represented
in the next cut. Here seven of the marginal ganglia
having been removed as before, the eighth one was
made the point of origin of a circumferential section,
which was then carried round and round the bell in
the form of a continuous spiral — the result, of course,
being this long ribbon-shaped strip of tissue with
the ganglion at one end and the remainder of
the swimming-bell at the other. Well, as before,
the contraction-waves always originated at the
ganglion ; but now they had to course all the way
along the strip until they arrived at its other ex-
tremity; and, as each wave arrived at that extremity,
it delivered its influence into the remainder of the
swimming-bell, which thereupon contracted. Now,
in this experiment, when the spiral strip is only
made about half an inch broad, it may be made
more than a yard long before all the bell is used up
in making the strip; and as nothing can well be
imagined as more destructive of the continuity of
a nerve-plexus than this spiral mode of section
must be, we cannot but regard it as a very remark-
able fact that the nerve-plexus should still continue
to discharge its function. Indeed, so remarkable does
this fact appear, that to avoid accepting it we may
well feel inclined to resort to another hypothesis,
namely, that these contraction- waves do not depend
for their passage on the nervous network at all,
but that they are of the nature of the muscle waves,
or of the waves which we see in undifferentiated
protoplasm, where all parts of the mass being equally
excitable and equally contractile, however severely

72 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

we cut the mass, as long as we do not actually
divide it, contraction-waves will pass throughout
the whole mass. But this very reasonable hypo-
thesis of the contraction-waves in the Medusae
being possibly nothing more than muscle- waves is
negatived by other facts, which I shall now proceed
to state.

In the first place, if a number of experiments be
tried in any of the three modes of section above
described, it will be found that extreme variations
are manifested as regards the degree of tolerance.
In the spiral mode of section, for instance, it will
sometimes happen that the contraction-wave will
become blocked when the contractile strip is only
an inch lono- while in other cases (as in the one
represented) the wave will continue to pass through
a strip more than thirty times that length ; and
between these two extremes there are all possible
grades of tolerance. Now it seems to me that if
the tissue through which these contraction-waves
pass is supposed (as far as they are concerned) to be
of a functionally homogeneous nature, no reason
can be assigned why there should be such great
differences in the endurance of the tissue in different
individual cases ; while, if we suppose that the
passage of the contraction-waves is more or less
dependent on the functional activity of the nervous
plexus which we know from microscopical examina-
tion to be present, Ave encounter no such difficulty ;
for it is almost to be expected that in some cases it
would happen that important nerves would soon be
encountered by the section, while in other cases it

SECTION OF COVERED-EYED MEDUSiE. 73

would happen that such nerves would escape the
section for a longer distance. It is indeed incredible
that anyone nerve should happen to pursue a spiral
course twice or thrice round the umbrella, and at
the same time happen to be concentric witli the
course pursued by the section ; but, as we shall
presently see, such an hy})othcsis as this is not
necessary to account for the facts.

Again, in the second place, strong evidence that
the passage of the contraction-waves is dependent
on the functional activity of the nervous plexus,
and therefore that they are not merely muscle-
waves, is furnished by the fact that at whatever
point in a spiral strip which is being progressively
elongated by section the contraction-wave becomes
blocked, the blocking is sure to take place coinjMely
and exclusively at that point. Now, as I have tried
this experiment a great number of times, and
always tried it by carefully feeling the way round
{i.e. only making a very short continuation of the
cut after the occurrence of each con tract ion- wave,
and so ver}^ precisely localizing the spot at which
the contraction- wave ceased to pass), I can scarcely
doubt that in every case the blocking is caused by
the cutting through of nerves.*

* In a liighly interesting paper recently published by Dr. W. H.
Gaskell, F.K.S., on " The Innervation of the Heart" (Journ. tf
Physiol. y vol. iv. p. 43, et seq.), it is shown that the experiments
in section thus far described yield strikingly similar results when
performed upon the heart of the tortoise and the heart of the
skate. Dr. Gaskell inclines to the belief that in these cases
the contraction-waves are merely muscle-waves. There is one
important fact, however, which even here seems to me to indicate

74} JELLY-FISH, STAR-FISII, AND SEA-URCHINS.

But, lastly, the strongest evidence in favour of
this view as affoi-Jed by the following observations.
At the beginning of this treatise I stated that the
distinguishing function of nerve consists in its power
of conducting stimuli to a distance, irrespective of
the passage of a contraction- wave ; and I may here
add that when a stimulus so conducted reaches a
ganglion, or nerve-centre, it causes the ganglion to
discharge by so-called " reflex action." Now, this
distinguishing function of nerve can plainly be
proved to be present in the Medusae. For instance,
take such a section of Aurelia as this one (Fig. 12),

that the propai^ation of the wave is at least in some measure
dependent on nervons conduction. This fact is, that after a
contraction-wave has been blocked by the severity of a spiral or
other form of section, it may again be made to force a passage
under the influence of vagus stimulatiou.

Moreover, in a paper still more recently published by Drs. Brunton
and Cash on " Electrical Stimulation of the Fi'og's Heart" (Proc.
Roy. 8')C., vol. XXXV., No. 227, p. 455, et seq.) it is remarked,
" Another interesting consideration is, whether the stimulus which
each cavity of the heart transmits to the succeeding one consists
in the propagation of an actual muscular wave, or in the
propagation of an impulse along the nerves. The observations
of Gaskell have given very great importance to the muscular
wave occurring in each cavity of the heart of cold-blooded animals
as a stimulus to the contraction of the next succeeding cavity.
Our observations appear to us to show that, while this is an
important factor, it is not the only one in the tiansmission of
stimuli. . . . We consider that stimuli are ahso propagated from
one chamber of the heart to another through nervous channels :
thus we find that irritation of the venus sinus will sometimes
produce simultaneous contractions of the auricle and ventricle,
ixastead of the ventricular beat succeeding the auricular in the
ordinary way. This we think is hardly consistent with the hypo-
thesis, that a stimulus consists of the propagation of a muscular
wave only from the auricle to the ventricle."

SECTION OF COVERED-EYED MEDUSJE.

/o

wherein the bell has been cut into the form of a
continuous parallelogram of tissue with the ovaries
and a single remaining ganglion at one end. (The

cuts interposed in the parallelogram may, for the
present, be disregarded.) Novv% if the end mai ked a

76 JELLY-FISH, STAR-FISH, AND SEA-URCHIXS.

of the neuro-muscular sheet most remote from the
ganglion be gently brushed with a camel's hair
brush — i.e. too gently to start a responsive contrac-
tion-wave— the ganglion at the other end will
shortly afterwards discharge, as shown by its start-
incr a contraction-wave at its own end of the
parallelogram, h; thus proving that the stimulus
caused by brushing the tissue at the other end, a,
must have been conducted all the way along the
parallelogram to the terminal ganglion, 6, so causing
the terminal crano^lion to discharcje bv reflex action.
Indeed, in many cases, the passage of this nervous
wave of stimulation admits of being seen. For the
numberless tentxicles which frin^re the maro-in of
Aurelia are more higlily excitable than is the
general contractile tissue of the bell; so that on
brushing the end a of the parallelogram remote
from the ganglion, the tentacles at this end respond
to the stimulus by a contraction, then those next in
the series do the same, and so on — a wave of con-
traction being thus set up in the tentacular fringe,
the passage of which is determined by the passage
of the nervous wave of stimulation in the super-
jacent nervous netwoik. This tentacular wave is
in the illustration represented as having travelled
nearlv half the whole distance to the terminal o-ancr-
lion, and when it reaches that ganglion it will cause
it to discharge by reflex action, so giving rise to a
visible wave of muscular contraction passing in the
direction h a, opposite to that which the nervous or
tentacular wave had previously pursued. Now this
tentacular wave, being an optical expression of a pas-

SECTION OF COVER ED- EYED MEDUSAE. 77

sage of a wave of stimulation, is a siglit as beautiful
as it is unique ; and it affords a first-rate oppor-
tunity of settling tlds all-important (question, namely,
Will this conductile or nervous function prove
itself as tolerant towards a section of the tissue as
the contractile or muscular function has already
proved itself to be ? For, if so, we shall gain nothing
on the side of simplicity by assuming that the
contract ^on-^yilveii are merely muscle- waves, so long
as the conduction or unclouhfcclly nervous waves
are equal 1}^ able to pass round sections interposed
in their path. Briefly, then, I find that the nervous
waves of stimulation are quite as able to pass round
these interposed sections as are the waves of con-
traction. Thus, for instance, in this specimen (Fig.
12), the tentacular wave of stimulation continued
to pass as before, even after I had submitted the
parallelogram of tissue to the tremendously severe
form of section which is represented in the illustra-
tion; and this fact, in my opinion, is one of the most
important that has been brought to light in the whole
range of invertebrate physiology. For what does it
prove ? It proves that the distinguishing function
of nerve, where it first appears upon the scene of
life, admits of being performed vicariously to almost
any extent by all parts of the same tissue-mass. If
we revert to our old illustration of the muslin as
representing the nerve-plexus, it is clear that, how-
ever much we choose to cut the sheet of muslin with
such radial or spiral sections as are represented in
the illustrations, one could alwa^'s trace the threads
of the muslin with a needle round and round the

78 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

disc, without once interrupting the continuity of
the tracing; for on coming to the end of a divided
thread, one could always double back on it and
choose another thread which might be running in
the required direction. And this is what we are
now compelled to believe takes place in the fibres
of this nervous network, if we assume that these
visible fibres are the only condactile elements which
are present. Whenever a stimulus wave readies a
cut, we must conclude that it doubles back and
passes into the neighbouring fibres, and so on, time
after time, till it succeeds in passing round and
round any number of overlapping cuts.

This is, no doubt, as I have already observed, a
very remarkable fact ; but it becomes still more so
when we have regard to the histological researches
of Professor Schafer on the structural character of
this nerve-plexus. For these researches have shown
that the nerve-fibres which so thickly overspread
the muscular sheet of Aurelia do not constitute a
true plexus, but that each fibre is comparatively
short and nowhere joins with any of the other
fibres; that is to say, although the constituent
fibres of the network cross and recross one another
in all directions — sometimes, indeed, twisting round
one another like the strands of a rope — they can
never be actually seen to join, but remain anatomi-
cally insulated throughout their length. So that the
simile by which I have represented this nervous
network — the simile, namely, of a sheet of muslin
overspreading the whole of the muscular sheet — is,
as a simile, even more accurate than has hitherto

SECTION OF COVERED-EYED MEDUSA. 79

appeared ; for just as in a piece of muslin the con-
stituent threads, although frequently meeting one
another, never actually coalesce, so in the nervous
network of Aurelia, the constituent fibres, although
frequently in contact, never actually unite.

Now, if it is a remarkable fact that in a fully
differentiated nervous network the constituent
fibres are not improbably capable of vicarious action
to almost any extent, much more remarkable does
this fact become when we find that no two of these
constituent nerve-fibi-es are histologically continuous
with one another. Indeed, it seems to me we have
here a fact as startling as it is novel. There can
scarcely be any doubt that some influence is com-
municated from a stimulated fibre a to the adjacent
fibre h at the point where these fibres come into close
apposition. But what the nature of the process
may be whereb}^ a disturbance in the excitable
protoplasm of a sets up a sympathetic disturbance
in the anatomically separate protoplasm of 6,
supposing it to be really such — this is a question
concerning which it would as yet be premature
to speculate. But I think it may be well for
physiologists to keep awake to the fact that a
process of this kind probably takes place in the
case of these nerve-fibres. For it thus becomes a
possibility which ought not to be overlooked, that
in the fibres of the spinal cord, and in ganglia
generally, where hi.stologists have hitherto been un-
able to trace any anatomical or structural continuity
between cells and fibres, which must nevertheless
be supposed to possess physiological or functional

80 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

continuity — it thus becomes a possibility that in
these cases no such anatomical continuity exists,
but that the pliysiological continuity is maintained
by some such process of physiological induction as
probably takes place among the nerve-fibres of
Aurelia.*

I have now to detail another fact of a very
puzzling nature, but one which is certainly of
importance. When the spiral section is performed
on Aurelia auvita, and when, as a consequence, the
contraction-waves which traverse the elongating
strip become at some point suddenly blocked, if the
section be stopped at this point it not unfrequently
happens that after a time the blocking suddenly
ceases, the contraction -waves again passing from
the strip into the umbrella as freely as they did
before the section reached the point at which the
blocking occurred. The time required for this
restoration of physiological continuity is very
variable, the limits being from a few seconds to an
hour or more ; usually, however, it is from two
to four minutes. This process of i e-establishing
the physiological connections, although rapid, is
not so instantaneous as is that of their destruction
by section. In general it requires the passage of
several contraction- waves before the barrier to the
passage of succeeding waves is completely thrown

* That it can scarcely be electrical induction would seem to be
shown by the fact that such effects can only be produced on
nerves by strong currents, and also by the fact that the saline
tissuesof the swimming.bell must sTiort-circuit any feeble electncal
currents as soon as they are genoratnd.

SECTION OF COVERED-EYED MEDUS.E. 81

down. The first wave wliich effects a passage
appears to have nearly all its force expended
in overcoming the barrier, the residue being only
sufficient to cause a very feeble, and sometimes
almost imperceptible, contraction of the umbrella.
The next Avave, however, passes across the barrier
with more facility, so that the resulting contraction
of the umbrella is more decided. The third wave,
again, causes a still more pronounced contraction of
the umbrella ; and so on with all succeeding waves,
until every trace of the previous blocking has
disappeared. When this is the case, it generally
happens that the strip will again admit of being
elongated for a short distance before a blocking of
the contract! on- waves again supervenes. Sometimes
it will be found that this second blockage will also
be overcome, and that the strip will then admit of
being still further elongated without the passage
of the waves being obstructed ; and so on occa-
sionally for three or four stages.

The same series of phenomena may be shown in
another way. If a contractile strip of tolerable
length be obtained, with the waves passing freely
from one end to the other, and if a series of parallel
and equidistant cuts be made along one side of the
strip, in a direction at right angles to the length,
and each cut extending two-thirds of the breadth
of the strip, the chances are in favour of the con-
traction-waves being wholly unaffected by the sec-
tions, however numerous these may be. But now, if
another series of parallel and equidistant cuts of the
same length as the first ones, and alternating with

82 JELLY-FISn, STAR-FlSir, AND SEA-URCHINS.

them, be made along the other side of tlie contractile
strip, the result is, of course, a number of interdigi-
tating cuts ; and it is easy to see that by beginning
with a few such cuts and progressively increasing
their number, a point must somewhere be reached
at which one portion will become physiologically
separated from the rest. The amount of such
section, however, Avhich contractile strips will some-
times endure is truly surprising. I have seen such
a strip twenty inches long by one and a half inches
wide with ten such cuts along each side, and the
contraction- waves passing without impediment from
end to end. But what I wish more especially to
observe just now is, that by progressively increasing
the number of such interdigitating cuts up to the
point at which the contraction- wave is blocked, and
then leaving the tissue to recover itself, in many
cases it will be observed that the blocking is sooner
or later overcome; that on then adding more
interdigitating cuts the blocking again supervenes ;
but that in time it may again be overcome, and so
on. It is, however, comparatively rare to find cases
in which blocking is overcome twice or thrice in
succession.

Section is not the only way in which blocking of
waves may be caused in contractile strips. I find
that pressure, even though very gentle, exerted on
any part of a strip causes a blocking of the waves
at that part, even after the pressure has been
removed. If the pressure has been long continued,
after its removal the blocking will probably be
permanent; but if the pressure has been only of

SECTION OF COVER KD-EYED MEDUSAE. 83

short duration, the blocking will most likely be
transitory. Even the slight btrains caused by hand-
ling a contractile strip in the air are generally
followed by a decrease in the rate of tlie waves, and
sometimes by their being completely blocked. Other
methods by which the passage of weaves in contrac-
tile strips admits of being blocked will be alluded
to farther on.

Now, in all these cases of temporary blocking we
must conclude that when the contraction-waves
succeed in at last forcing a passage, some structural
change has taken place in the tissue at the region
of injury, corresponding with the functional change
of the re-establishment of physiological continuity.
The waves previously stopped at a certain point of
section or otherwise, after beating for a time on the
physiological barrier, are at last able to throw doAvn
the barrier, and thenceforward to proceed on their
way unhindered. What, then, is the nature of the
structural change which has taken place ?

In the early days of this research, before the
presence of a nerve-plexus had been proved histo-
logically, I argued in favour of such a plexus on the
grounds furnished by many of the foregoing ex-
periments; and at a lecture given in the Royal
Institution I ventured to say that if a careful
investigation of the histology of these tissues should
fail to show the plexus which the result of those
experiments required me to assume, we should still
be compelled to suppose that the plexus w^as pre-
sent, although not sufficiently differentiated lo
admit of being seen. I further ventured to suggest

84 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

that in this event the facts just stated might be taken
to substantiate the theory of Mr. Herbert Spencer*
on the genesis of nerve- tissue in general. This
theory is that which supposes incipient conductile
tissues, or rudimentary nerve-fibres, to be differ-
entiated from the surrounding contractile tissues, or
homogeneous protoplasm, by a process of integra-
tion which is due simply to use; so that just as
water continually widens and deepens the channel
through which it flows, so molecular or nervous
waves of stimulation, by always flowing through
the same tissue-tract^, tend ever more and more to
excavate for themselves functionally differentiated
lines of passage.

Such being Mr. Spencer's theory, I applied it
hypothetically to the above facts in the words
which I may here quote.

"As the successive waves beat rhythmically on
the area of obstruction, more or less of the mole-
cular disturbances must every time be equalized
throuQfh these lines of discharo-e, which from the
first have been almost sufficient to maintain the
physiological continuity of the tissue. Therefore,
according to the hypothesis, every wave that is
blocked imposes upon these particular lines of dis-
charge a much higher degree of functional activity
than they were ever before required to exercise ;
and this greater activity causing in its turn greater
permeability, a point will sooner or later arrive at
v/hich these lines of discharge, from having been
almost, become quite able to draft off sufficient
molecular motion, or stimulating influence, to carry

SECTION OF COVERED-EYED MEDUSA. 85

on the contraction-waves beyond the areas of
previous blocking. In such instances, of course, v^^e
should expect to find wliat I always observed to be
the case, viz. that the first contraction- wave which
passes the barrier is only very feeble, the next
stronger, the next still stronger, and so on, accord-
ing as the new passage becomes more and more per-
meable by use, until at last the contract ion- waves
pour over the original barrier without any per-
ceptible diminution of their force. In some cases,
by exploring with graduated stimuli and needle-
point terminals, I was able to ascertain the precise
line through which this eruption of stimulating
influence had taken place."

I have now to state the effect upon this hypo-
thesis which in my opinion has been produced by
the histological proof that the plexus in question is
composed of fully differentiated nerves. Briefly,
then, I think that the hypothesis still holds to the
extent of being the only one available whereby to
explain the facts ; but there is this great difference,
viz. that the hypothesis need not now be applied
to the genesis of nerve-tissue out of comparatively
undifferentiated contractile tissue, but rather to the
increasing of the functional activity of already well-
differentiated nerve-tissue. In other words, we
have not now to suppose that nerve-tissue is
formed de novo in the region of blocking ; but, in my
opinion, we still have to suppose that the nerve-
libres which were already there have their func-
tional capabilities so far improved by the greater
demand imposed upon them, that whereas at first

86 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

they were not able, eventually they became able to
draft off enough molecular disturbance to carry on
a stimulus adequate to cause a muscular contraction.
It will be observed that the difference thus ex-
pressed is one of considerable importance; for now
the facts cease to lend any countenance to Mr.
Spencer's theory touching the formation of nerves
out of protoplasm, or other contractile material.
They continue, however, to countenance his views
touching the improvement of functional capacity
which nerve-fibres, when already formed, undergo
by use; and this, wliich is in itself an important
matter, is the point with which I was mainly con-
cerned in the lecture of the Royal Institution just
alluded to. For, as I then observed, in this theory
of nerve-fibres becoming more and more functionally
developed by use, we probably have a physical ex-
planation, which is as full and complete as such an
explanation can ever be, of the genesis of mind.
" For from the time that intelligence first dawned
upon the scene of life, whenever a new relation had
to be established in the region of mind, it could only
be so established in virtue of some new line of dis-
charge being excavated through the substance of
the brain. The more often this relation had to
be repeated in the mind, the more often would
this discharge require to take place in the brain,
and so the more easy would every repetition of
the process become. . . . Thus it is, according to
the theory, that there is always a precise proportion
between the constancy with which any relations
have been joined together during the history of

SECTION OF COVEKED-EYED MEDUS.E. 87

intelligence, and the difficulty which intelligence
now experiences in trying to conceive of such
relations as disjoined. Thus it is that, even during
the history of an individual intelligence, 'practice
makes perfect,' by frequently repeating the needful
stimulations along the same lines of cerebral dis-
charge, so rendering the latter ever more and more
permeable by use. Thus it is that a child learns
its lessons by frequently repeating them ; and thus
it is that all our knowledge is accumulated."*

Rate of Transmission of Stiniull.

The rate at which contraction-waves traverse
spiral strips of Aurelia is variable. It is largely
determined by the length and width of the strip ; so

* I have associated the above theory of nerve-genesis with the
name of Mr. Spencer, because it occupies so prominent a place in
his " Principles of Psychology." But from what I have said in
the text, I think it is clear that the theory, as presented by Mr.
Spencer, consists of two essentially distinct hypotheses — the one
relating to the formation of nerve-tissue out of protoplasm, and
the other to the increase of functional capacity in a nerve-fibre
by use (a third hypothesis of Mr. Spencer relating to the
formation of ganglion-tissue does not here concern us). The
latter hypothesis, however, ought not to be associated with Mr.
Spencer's name without explaining that it has likewise occurred to
other writers, the first of which, so far as I can ascertain, was La-
marck, who says, "Dans toute action, le fluide des nerfs qui la
provoque, subit un mouvement de deplacement qui y donne lieu.
Or, lorsque cette action a ete plusieurs fois repe'tce, il n'est pas
douteux que le fluid qui I'a exe'cutee, ne se soit fraye une route,
qui lui devient alors d'autanfc plus facile a parcourir, qu'il l*a
effectivement plus souvant francliie, et qu'il n'ait lui-meme une
aptitude plus grand a suivre cette route frayee que celles qui le
sunt niuins." ("Phil. ZooL," torn ii. pp. 318-19.)

88 JKLLY-FISH, STAR-FISH, AND SEA-UPtCHlNS.

that the best form of strip to use for the purpose of
ascertaining the inaximum rate is one which I shall
call the circular strip. A circular strip is obtained
by first cutting out the central bodies {i.e. manu-
brium and ovaries), and then, with a single radial
cut, converting the animal from the form of an
open ring to that of a continuous band. I dis-
tinguish this by the name " circular " band or strip,
because the two ends tend to preserve their original
relative positions, so giving the strip more or less of
a circular form. Such a strip has the advantage
of presenting all the contractile tissue of the
swimming-bell in one continuous band of the
greatest possible width, and is therefore the form
of strip that yields the maximum rate at which
contraction-waves are able to pass. The reason
why the "inaxirtiiim rate should be the one sought
for is because this is the rate which must most
nearly approximate the natural rate of contraction-
waves in the unmutilated animal. This rate, at the
temperature of the seaand with vigorous specimens,
I find to be eighteen inches per second.

In a circular strip the rate of the waves is uniform
over the whole extent of the strip ; so that the time
of their transit from one point to another varies
directly as the length of the strip. But on now
narrowing such a strip, although the rate is thus
slowed, the relation between the narrowing and the
slowing is not nearly so precise as to admit of our
saying that the rate varies inversely as the width.
The following figure will serve to show the propor-
tional extent to which the passage of contraction-

StX'TION OF COVKUIiD-KVKI) MKDrS.E.

89

waves is retarded by narrowing the area through
which they pass : —

Time from oiul to end of a

circular stiip
Time after width has been

reduced to one-half
Time after width has been

reduced to one-quarter...
Time after width has been

reduced to one-eighth ...

In such experiments it generally happens, as here
represented, that reducing the width of a circular
strip by one-half produces no effect, or only a sli. ht
effect, on the rate, while further narrowing to the
degree mentioned produces a conspicuous effect.
I may also state that if, as occasionally happens, the
immediate effect of narrowing a circular strip to one-
half is to temporarily block the contraction-waves,
when the latter again force their passage, their rate
is sloAver than it was before. It seems as if the
more pervious tissue tracts having been destroyed
by the section, the less pervious ones, though still
able to convey the contraction-wave, are not able
to convey it so rapidly as were the more pervious
tracts.

In order to ascertain whether certain zones of the
circular contractile sheet in all individuals habitually
convey more of the contractile influence than do
other zones, I tried a number of experiments in the
following form of section. Having made a circular
strip, I removed all the lithocysts save one, and
then cut the strip as represented in Fig. 14. On

90 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

now stimulating the end a, or on watching the
lithocyst there discharge, the resulting contraction-
wave would be observed to bifurcate at h, and then

pass on as two separate waves through the zones,
h c,b d. Now, as these two waves were started at

SECTION OF COVERKD-EYED MEDUS.^. 91

the same instant of time, tliey ran, as it were, a race
in the two zones, and in this way the eye could
judge with perfect ease which wave occupied the
shortest time in reaching its destination. This ex-
periment couUl be varied by again bisecting each of
these two zones, thus making four zones in all, and
four waves to run in each race. A number of
experiments of this kind showed me that there is
no constancy in the relative conductivity of the
same zones in different individuals. In some in-
stances, the waves occupy less time in passing
through the zone h c than in passing through the
zone b d ; in other instances, the time in the two
zones is equal ; and, lastly, the converse of the
first-mentioned case is of equally frequent occur-
rence. Very often the waves become blocked in
h c, while ihej continue to pass in h d, and vice
versa. Now, all these various cases are what
we might expect to occur, in view of the variable
points at which contraction- waves become blocked
in spiral strips, etc. ; for if the contractile tissues
are not functionally homogeneous, and if the rela-
tively pervious conductile tracts are not constant
as to their position in different individuals, the
results I have just described are the only ones that
could be yielded by the experiments in question.
Considering, however, that in these experiments the
central zones are not so long as the peripheral
zones, I think it may fairly be said that the con-
ductile power of the latter is greater than that of
the former; for, otherwise, the above experiments
ought to yield a large majority of races won by the

92 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

waves that course through the central zones, and
this is not the case. Indeed, it is surprising how
often the race is, as it were, neck and neck, thus
showing that the relative conductivity of all the
zones is precisely adjusted to their relative lengths ;
and forasmuch as in the unmutilated animal this
adjustment must clearly serve the purpose of
securing to the con tractii)n- wave a passage of
uniform rate over the whole radius of the umbrella,
I doubt not that, if it were possible to perform the
race-course section without interrupting any of
the lines of conduction-tissue, neck and neck races
would be of invariable occurrence.

Interdigitating cuts, as might be expected, pro-
long the time of contraction-waves in their passage
through the tissue in which the cuts are interposed.
For example, in a spiral strip measuring twenty-six
inches in length, the time required for the passage
of a contraction -wave from one end to the other is
represented by the line a h in the annexed woodcut.
But after twenty interdigitating
cuts had been interposed, ten on
each side of the strip, the time
increased to c d, the line e f
Fig. 15. representing one second. And

more severe forms of section are, of course, attended
with a still more retarding influence.

The effects of temperature on the rate of con-
traction-waves are very striking. For instance, in
a rather narrow strip measuring twenty- eight inches
hmg and one and a half inches wide, the following
variations in rate occurred : —

SECTION OF COVERED-EYED MEDUS.E.

03

Temperature of water.

Time occnpiod in pass ge of
contractile waves.

26°
32°

42°
65°
75°
85°

4 seconds.
3 seconds.
2f seconds.
2 seconds.
1|- seconds.
Blocked.

Or,ad()pting again thegraphic method ofstateiuent,
these vai'iations may be represented as follows : —
26°

32°

42

65°

75°

85°

One second ... ^^_^^^^^_^^^

Fig. 16.

Submitting a contractile strip to slight strains has
also the effect of retarding the rate of the waves
while they pass through the portions of the strip
which have been submitted to strain. The method
of straining which I adopted was to pass my finger
below the strip, and then, by raising my hand, to
bring a portion of the strip slightly above the level
of the water. The in i table or contractile surface
was kept uppermost, and therefore suffered a gentle
strain ; for the weight of the tissue on either side
of the finger made the upper surface somewhat
convex. By passing the finger all the way along

94< JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

the strip in this way, the latter might be gently
strained througliout its entire length, the degree of
straining being determined by the height out of the
water to which the tissue was raised. Of course,
if the strip is too greatly strained, the contraction-
waves become blocked altogether, as described
above ; but shortly before this degree of straining
was reached, I could generally observe that the rate
of the waves was diminished. To give one instance,
a contractile strip measuring twenty -two inches had
the rate of its waves taken before and after strain-
ing of the kind described. The result was as
follows : —

Befoye straining...
After straining ..,
One second

Fig. 17.

Immediately after severe handling of this kind,
the retardation of contraction-waves is sometimes
even more marked than here represented; but I
think this may be paitly due to shock, for on
srivino; the tissue a little while to recover, the rate
of the waves becomes slightly increased.

Ansesthetics likewise have the effect of slowing
the rate of contraction-waves before blocking them.
Taking, for instance, the case of chloroform, a narrow
spiral strip between one and two feet long was
immersed in sea-water containing a large dose of
the anaesthetic ; the observations being taken at six
seconds' intervals, the following were the results: —

SECTION OF COVKRKD-EYKl) MEDUSAE.

Normal wiitor

Six secmiils after trans-
ference to chloroform

Six seconds later

Six seconds later

S i X seconds later

Six seconds later

One second

In such experiniL^nts, the recovery of the normal
rate in unpoisoned water is gradual. Taking, for
instance, the case of a spiral strip in morphia
(Fig. 19), it will be seen that the original rate
did not fully return. Some substances, however,
exert a more marked permanent effect of this kind
than do weak solutions of morphia. Here, for
instance, is an experiment with alcohol (see Fig. 20).

In normal water

yuart?r of an hour after
exposure to mopliia ...

One iniiiuieaft'.T strength-
ening dose

Four uiiiiut'-s later, and
just bel'on- blocking of
wave

Fifteen seconds lat r,wave
cimtinuing blocked

Innned lately alter pa-s.ige
of wave on r- toation
to nui inal sea-water . . .

Four minutes later

Quarter of an hour later...

An hour later

One second ... .,. ^^^--—^^—^■■■i™

Fig. la.

96 JELLY-FISH, STAR-FISH, AND SEA-URCHINS

In normal water

Quarter of an hour after
o.\posure to weak dose ...

Two minutes after strength-
ening of dose

Five minutes later, and just
before blocking of wave

Fifteen seconds later, wave
continuing blocked

Immediately after passage
of wave on restoration to
normal sea-water

An hour later

One second

Fig. 20.

From these experiments, however, it must not
be definitely concluded that it is the antesthesiating
property of such substances which exerts this slow-
ing and blocking influence on con traction- waves,
for 1 find that almost any foreign substance, whether
or not an anaesthetic, will do the same. That nitrite
of amyl, cafiein, etc., should do so, one would not
be very surprised to hear ; but it might not so readily
be expected that strychnine, for instance, should
block contraction- waves ; yet it does so, even in
doses so small as only just to taste bitter. Nay,
even fresh water completely blocks contraction-
waves after the strip has been exposed to its
influence for about half an hour, and exerts a per-
manently slowing efiect after the tissue is restored
to sea- water. These facts show the extreme sensi-
tiveness of the neuro-muscular tissues of the
Medusiie to any change in the character of their
surrounding medium, a sensitiveness which we
shall again have occasion to comment u})on when
treating of the effects of poisons.

SECTION OF COVERED-EYED MEDUSiE. 97

In conclusion, I may mention an interesting fact
which is probably connected with the summation
of stimuli before explained. When a contractile
strip is allowed to rest for a minute or more, and
when a wave is then made to traverse it, careful
observation will show that the passage of the first
wave is slower than that of its successor, provided
the latter follows the former after not too great an
interval of time. The difference, however, is exceed-
ingly slight, so that to render it apparent at all the
longest possible strips must be used, and even then
the experimenter may fail to detect the difference,
unless he has been accustomed to signalling, by
which method all these observations on rate have
to be made.

StiinvJiis-iuaves.

The rate of transmission of tentacular waves
is only one-half that of contraction- waves, viz.
nine inches a second. This fact appeared to me
very remarkable in view of the consideration that
the tentacular wave is the optical expression of a
stimulus-wave, and that there can be no conceivable
use in a stimulus- wave being able to pass through
contractile tissue independently of a contraction-
wave, unless the former is able to travel more
rapidly than the latter ; for the only conceivable use
of the stimulus-wave is to establish physiological
harmony between different parts of the organism,
and if this wave cannot travel more rapidly than
a contraction-wave which starts from the same
point, it would clearly fail to perform this function.

98 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

In view of this anomaly, I was led to think that
if the rate of the stimulus-wave is dependent in
a large degree on the strength of the stimulus that
starts it, the slow rate of nine inches a second
might be more than doubled, if, instead of using a
stimulus so gentle as not to start a contraction-
wave, I used a stimulus sufficiently strong to do
this. Accordingly I chose a specimen of Aurelia
wherein the occurrence of tentacular waves was
very conspicuous, and found, as I. had hoped, that
every time I stimulated too gently to start a con-
traction-wave, the tentacular wave travelled only
at the rate of nine inches a second ; whereas, if I
stimulated with greater intensity, I could always
observe the tentacular wave coursing an inch or
two in front of the contraction-wave.

It is remarkable, however, that in this, as in all
the other specimens of Aurelia which I experimented
upon, the reflex response of the manubrium was
equally long, whatever strength of stimulus I applied
to the umbrella ; or, at any rate, the time was only
slightly less when a contraction- wave had passed
than when only a tentacular wave had done so.
The loss of time, however, appears to take place in
the manubrium itself, where the rate of response
is astonishingly slow. Thus, if one lobe be irritated,
it is usually from four to eight seconds before the
other lobes respond. But the time required for
such sj^mpathetic response may be even more
variable than this — the limits I have observed
beino; as G:reat as from three to ten seconds. In all
cases, however, the response, when it does occur, is

SECTION OF COVERED-EYED MEDUSA 99

sudden, as if tlie distant lobe had then for the first
time received the stimulus. Moreover, one lobe —
usually one of those adjacent to the lobe directly
irritated — responds before the other two, and then
a variable time afterwards the latter also respond.
This time is, in most cases, comparatively short, the
usual limits being from a quarter of a second to two
seconds. How much of these enormous intervals is
occupied by the period of ganglionic latency, and
how much by that of transmission, it is impossible
to say; but I have determined that the rate of
transmission from the end of a lobe of the manu-
brium to a lithucyfc>o (deducting a second for the
double period of latent stimulation) is the same
as the rate of a tentacular wave, viz. nine inches a
second. The presumption, therefore, is that the
immense lapse of time required for reflex response
on the part of the manubrium is required by the
lobular ganglia, or whatever element it is that here
performs the ganglionic function.

Exhaustion,

In various modes of section of Aurelia I have
several times observed a fact that is worth record-
ing. It sometimes happens that w^hen the con-
necting isthmus between two almost severed areas
of excitable tissue is very narrow, the passage of
contraction-waves across the isthmus depends upon
the freshness, or freedom from exhaustion, of the
tissue which constitutes the isthmus. That is to
say, on faratlizing one of the two tissue-areas which

100 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

the isthmus serves to connect, the resulting con-
traction-waves will at first pa^^s freely across the
isthmus ; but after a time it may happen in some
preparations that every now and then a contraction-
wave fails to pass across the isthmus. When this
is the case, if the stimulation is still continued, a
greater and greater proportion of waves fail to pass
across the isthmus, until perhaps only one in every
five or six becomes propagated from the one area to
the other. If single induction-shocks be then sub-
stituted for the faradaic stimulation, it may be found
that by leaving an interval of four or five seconds
between the successive shocks, every w^ave that
is started in the one area will be propagated across
the isthmus to the other area. But if the interval
between the successive shocks be reduced to two or
three seconds, every now and then a wave will fail
to pass across the isthmus; and if the interval be
still further reduced to one second, or half a second,
comparatively few of the waves will pass across.
Now, however, if the tissue be allowed five minutes'
rest from stimulation, and the single shocks be
thrown in at one second's intervals, all the first six
or ten waves will pass across the isthmus, after
which they begin to become blocked as before. It
may be observed also that when the waves are thus
blocked, owing to exhaustion of the connecting
isthmus, they may again be made to force a passage
by increasing the intensity of the stimulation, and
so giving rise to stronger waves having a greater
power of penetration. Thus, on re-enforcing the
electrical stimulus with the simultaneous application

SECTION OF COVERED-EYED MEDUSiE. 101

of a drop of spirit, the resulting waves of contraction
are almost sure to pass across the isthmus, even
though this has been exhausted in the manner just
described.

Ganglia appearing to assert their Influence at a
Distance from their own Seat.

Another fact, which I liave several times noticed
during my sections of Aurelia, also deserves to be
recorded. I have observed it under several modes
of section, but it will be only necessary to describe
one particular case.

In the Aurelia of a portion of which the accom-
panying woodcut (p. 102) is a representation, seven
of the lithocysts were removed, while the remaining
one was almost entirely isolated from the general
contractile tissue by the incisions aa, 66, cc. The
lithocyst continued to animate the tissue-area xxxx,
and through tlie connecting passage y the con-
traction-waves spread over the remainder of the
sub-umbrella tissue zzzz. So far, of course, the facts
were normal ; but very frequently it was observed
that the contraction-waves did not start from the
lithocyst, or from the area xxxx, but from the point
o in the area zz. After this origination of the
contraction-waves from the point o had been ob-
served a great number of times, I removed the
lithocyst. Tiie effect was not only to prevent the
further origination of contraction- waves in the area
xxxx, but also to prevent their further origination
from the point o, the entire umbrella thus becom-

102 JELLY-FISII, STAR-FISH, AND SEA-URCHINS.

ing paralyzed. Hence, before the removal of the
lithocyst, the contraction-waves which originated
at the point o, no less than those which originated
at the lithocyst itself, must in some way or other
have been due to the ganglionic influence emanat-
ing from the lithocyst and asserting itself at the
distant point o.

Fig. 21.

This property, which lithocysts sometimes present,
of asserting their ganglionic influence at a distance
from their own locality, can only, I think, be ex-
plained by supposing that at the point where under
these circumstances the contractions originate,
there are situated some scattered gano-lionic cells of

SECTION OF COVERED- EYED MEDUSAE. 103

consideraLle functional power, but yet not of power
enough to originate contraction-waves unless re-
enforced by some stimulating iniiuence, which
reaches them from the lithocyst through the
nervous plexus.

Regeneration of Tissues,

The only facts which remain to be stated in the
present chapter have reference to the astonishing
rapidity with which the excitable tissues of the
Medusae regenerate themselves after injury. In
this connection I have mainly experimented on
Aurelia aurita, and shall, therefore, confine my
remarks to this one species.

If with a sharp scalpel an incision be made
through the tenuous contractile sheet' of the sub-
umbrella of Aurelia, in a marvellously short time
the injury is repaired. Thus, for instance, if such
an incision be carried across the whole diameter of
the sub-umbrella, so as entirely to divide the excit-
able tissues into two parts while the gelatinous
tissues are left intact, the result of course is that
physiological continuity is destroyed between the
one half of the animal and the other, while the form
of the whole animal remains unchanged — the much
greater thickness of the uninjured gelatinous tissues
serving to preserve the shape of the umbrella. But
although the contractile sheet which lines the
umbrella is thus completely severed throughout its
whole diameter, it again reunites, or heals up, in
from four to eight hours after the operation.

CHAPTER V.

EXPERIMENTS IN SECTION OF NAKED-EYED MEDUSAE.

Distribution of Nerves in Sarsia.

My experiments have shown that the nervous
system in the naked-eyed Medusse is more highly
organized, or integrated, than it is in the covered-
eyed Medusae ; for whereas in the latter I obtained
no evidence of the gathering together of nerve-
fibres into definite bundles or trunks (the plexus
being evenly distributed over the entire surface of
the neuro-muscular sheet lining the umbrella), in
the former I found abundant evidence of tliis
advance in organization. And as the experiments
in this connection serve to substantiate the histo-
logical researches of Professors Haeckel, Schultz,
Eimer, and Hertwig, in as far as the distribution of
the main nerve-trunks is concerned, I shall here
detail at some length the character and results of
these experiments in the case of Sarsia.

The occurrence of reflex action in Sarsia is of
a very marked and unmistakable character. I may
begin by stating that when any part of the internal
surface of the bell is irritated, the manubrium
responds; but as there is no evidence of ganglia

SECTION OF NAKED-EYED MEDUSA 105

occurring in the manubrium, tliis cannot properly
be regarded as a case of reflex action. But now
the converse of the above statement is likewise true,
viz. that when any part of the manubrium is irri-
tated, the bell responds ; and it is in this that the
unequivocal evidence of reflex action consists, for
while the sympathy of the manubrium with the
bell is not in the least impaired by removing the
marginal ganglia of the latter, the sympathy of
the bell with the manubrium is by this operation
entirely destroyed.

We have thus very excellent demonstration of
the occurrence of reflex action in the Medusae.
Further experiments show that the reflex action
occurs, not between the marginal ganglia and every
part of the manubrium, but only between the
marginal ganglia and the point of the bell from
which the manubrium is suspended — it being only
the pull which is exerted upon this point when
the manubrium contracts that acts as a stimulus
to the marginal ganglia. But the high degree of
sensitiveness shoAvn by the marginal ganglia to the
smallest amount of traction of this kind is quite as
remarkable as their lack of sensitiveness to dis-
turbances going on in the manubrium.

Turning now to the physiological evidence of
the distribution of nerves in Sarsia, when one of
the four tentacles is very gently irritated, it alone
contracts. If the irritation be slightly stronger, all
the four tentacles, and likewise the manubrium,
contract. If one of the four tentacles be irritated
still more strongly, the boll responds with one or

106 JELLY-FISH, STAR-FISH, AND SEA-URCHINS

more locomotor contractions. If in the latter case
the stimulus be not too strong, or, better still, if the
specimen operated on be in a noii-vigorous or in
a partly ansesthesiated state, it may be observed
that a short interval elapses between ihe response
of the tentacles and that of the bell. Lastl}^, the
manubrium is much more sensitive to a stimulus
applied to a tentacle, or to one of the marginal
bodies, than it is to a stimulus applied at any other
part of the nectocalyx.

These facts clearly point to the inference that
nervous connections unite the tentacles with one
another and also with the manubrium ; or, perhaps
more precisely, that each marginal body acts as
a co-ordinating centre between nerves proceeding
from it in four directions, viz. to the attached
tentacle, to the margin on either side, and to the
manubrium. This, it will be observed, is the distri-
bution which Haeckel describes as occurring in
Geryonia, and Schultz as occuriing in Sarsia. It is,
further, the distribution to which m}^ explorations
by stimulus would certainly point. But, in order
to test the matter still more thoroughly, I tried the
effects of section in destroying the physiological
relations which I have just described. These effects,
in the case of the tentacles, were sufficiently precise.
A minute radial cut (only just long enough to
sever the tissues of the extreme margin) introduced
between each pair of adjacent marginal bodies
completely destroyed the physiological connection
between the tentacles. If only three marginal cuts
were introduced, the sympathy between those two

SECTION OF NAKliD-KYLl) MEDUSAE. 107

adjacent tentacles between wliicli no cut was made
continued unini|)aired, while the sympathy between
them and the other tentacles w^as destroyed.

The nervous connections between the tentacles
and the manubrium are of a more general character
than those described between the tentacles them-
selves; that is to say, severing the main radial
nerve-trunks produces no appreciable effect upon
the sympathy between the tentacles and the
manubrium.

The nervous connections between the whole
excitable surface of the nectocalyx and the manu-
brium are likewise of this general character, so that,
whether or not the radial nerve-trunks are divided,
the manubrium will respond to irritation applied
anywhere over the internal surface of the nectocalyx.
The manubrium, however, shows itself more sensitive
to stimuli applied at some parts of this surface than
it is to stimuli applied at other parts, although in
different specimens there is no constancy as to the
position occupied by these excitable tracts.

Distribution of Kerves in Tiarojjsis Indicans.

We have seen that in Sarsia reflex action obtains
between the manubrium and the nectocalyx; we
shall now see that in Tiaropsis indicans something
resembling reflex action obtains between the
nectocalyx and the manubrium. The last-named
species is a new one, which I have described else-
where, and I have called it " indicans " from a
highly interesting and important peculiarity of

108 JELLY-FISH, STAR-FISH, AND SEA-URCHINS

function which is manifested by its manubrium. The
Medusa in question measures about one and a half
inches in diameter, and is provided with a manu-
brium of unusual proportional size, its length being
about five-eigjhths of an inch, and its tliickness

Fig. 22.

being also considerable. Now, if any part of the
nectocalyx be irritated, the following series of
phenomena takes place. Shortly after the applica-
tion of the stimulus, the large manubrium suddenly
contracts — the appearance presented being that of
an exceedingly rapid crouching movement. The

SECTION OF NAKED-EYED MEDUSAE. 109

crouching attitude in which this movement termi-
nates continues for one or two seconds, after wliich
the organ begins gradually to resume its former
dimensions. Concurrently with these movements
on the part of the manubrium, the portion of the
nectocalj^x which has been stimulated bends inwards
as far as it is able. The manubrium now begins to
deflect itself towards the bent-in portion of the
nectocalyx ; and this deflection continuing with
a somewhat rapid motion, the extremity of the
manubrium is eventually brought, with unerring
precision, to meet the in-bent portion of the necto-
calyx. I here introduce a drawing of more than
life-size to render a better idea of this "pointing
action by the manubrium to a seat of irritation
located in the bell. It must further be stated that
in the unmutilated animal such action is quite
invariable, the tapered extremity of the manubrium
never failing to be placed . on the exact spot in the
nectocalyx where the stimulation is being, or
had previously been, applied. Moreover, if the
experimenter iriitates one point of the nectocalyx,
with a needle or a fine pair of forceps for instance,
and while the manubrium is applied to that
point he irritates another point, then the manu-
brium will leave the first point and niove over
to the second. In this way the manubrium may be
made to indicate successively any number of points
of irritation ; and it is interesting to observe that
when, after such a series of irritations, the animal
is left to itself, the manubrium will subsequently
continue for a considerable time to visit first one

no JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

and then another of the points which have been
irritated. In such cases it usually dwells longest
and most frequently on those points wdiich have
been irritated most severely.

I think the object of these movements is probably
that of stinging the offending body by means of the
urticating cells with which the extremity of the
manubrium is armed. But, be the object what it
may, the fact of these movements occurring is a
highly important one in connection with our study
of the distribution of nerves in Medusae, and the
first point to be made out with regard to these
movements is clearly as to whether or not they are
truly of a reflex character. Accordingly, I first
tried cuttino^ off the marg^in, and then irritatino^ the
muscular tissue of the bell ; the movements in
question were performed exactly as before. I was
thus led to think it probable that the reflex centres
of which I was in search might be seated in the manu-
brium. Accordingly, I cut oft* the manubrium, and
tried stimulating its own substance directly. I
found, however, that no matter how small a portion
of this organ I used, and no matter from wdiat part
of the organ I cut it, this portion would do its best
to bend over to the side which I irritated. Simi-
larly, no matter how short a stump of the manu-
brium I left in connection with the nectocalyx, on
irritating any part of the latter, the stump of the
manubrium would deflect itself towards that part
of the bell, although, of course, from its short length
it was unable to reach it. Hence there can be no
doubt that every portion of the manubrium — down,

SECTION OF NAKED-EYED MEDUSJE. Ill

ab least, to the size which is compatible with con-
ducting these experiments — is independently en-
dowed with the capacity of very precisely localizing
a point of irritation which is seated either in its
own substance or in tliat of the bell.

We have here, then, a curious fact, and one
which it will be well to bear in mind during our
subsequent endeavours to frame some sort of a con-
ception regarding the nature of these primitive
nervous tissues. The localizing function, which is
so very efficiently performed by the manubrium of
this Medusa, and which if anything resembling it
occurred in the higher animals would certainly
have definite ganglionic centres for its structural
co-relative, is here shared equally by every part of
the exceedingly tenuous contractile tissue that
forms the outer surface of the organ. I am not
aware that such a diffusion of ganglionic function
has as j^et been actually proved to occur in the
animal kingdom, but I can scarcely doubt that
future investigation will show such a state of things
to be of common occurrence among the lower
members of that kingdom.*

* The only case I know which rests on direct observation, and
which is at all parallel to the one above described, is the case of
the tentacles of Drosera. Mr. Darwin fonnd, when he cut ofE the
apical gland of one of these tentacles, together with a small por-
tion of the apex, that the tentacle thus mutilated would no longer
respond to stimuli applied directly to itself. Thus far the case
dillers from that of the manubrium of Tiaropsis indicans, and, in
respect of localization of co-ordinating function, resembles that
of ganglionic action. But Mr. Darwin also found that such a
*' headless tentacle " continued to be influenced by stimuli applied
to the glands of neighbouring tentacles — the headless one in that

112 JELLY-FISH, STAR-FLSH, AND SEA-URCHINS.

I shall now proceed to consider the nature of the
nervous connections between the nectocalj^x and
manubrium of this Medusa.

Bearing in mind that in an unmutilated Tiaropsis
indicans the manubrium invariably localizes with
the utmost precision any minute point of irrita-
tion situated in the bell, the significance of the
following facts is unmistakable, viz. that when a
cut is introduced between the base of the manu-
brium and the point of irritation in the bell, the
localizing power of the former, as regards that point
in the latter, is wholly destroyed. For instance, if
such a cut as that represented at a (see Fig. 22) be
made in the nectocalyx of this Medusa, the manu-
brium will no longer be able to localize the seat of
a stimulus applied below that cut, as, for instance,
at h. Now, having tried this experiment a number
of times, and having always obtained the same
result, I conclude that the nervous connections be-
tween the nectocalyx and the manubrium, which
render possible the localizing action of the latter,
are connections the functions of which are intensely
sjDecialized, and the distribution of which is radial.

So far, then, we have highly satisfactory evidence
of tissue-tracts performing the function of afferent
nerves. But another point of interest here arises.
Although, in the experiment just described, the

case bending over in whatever direction it was needful for it to
bend, in order to approach the seat of stimulation. This shows
that the analogue of ganglionic function must here be situated in
at least more than one part of a tentacle ; and I think it is not
improbable that, if trials were expressly made, this function would
be found to be diffused throughout the whole tentacle.

SECTION OF NAKED-EYED MEDUS.E. 113

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 someiuhere ; 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 offending 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 stimulation is
proceeding, and will then suddenly move over and
apply its extremity, perhaps to the point that is
opposite to the one which it is endeavouring to find.
It will then suddenly leave this point and try an-
other, and then another, and anothei-, and so on, as
long as the stimulation is continued. Moreover, it
is important to observe that there are gradations
between the ability of the manubrium to localize
correctly and its inability to localize at all, these
gradations being determined by the circum-
ferential distance from the end of the cut and
the point of stimulation. For instance, in Fig. 22,
suppose a cut A B, quarter of an inch long, to be
made pretty close to the margin and concentric
with it, then a stimulus applied at the point c, just
below the middle point of A B, would have the effect
of making the manubrium move about to various
parts of the bell, without being able in the least
degree to localize the seat of irritation. But if
the stimulus be applied at d, the manubrium will

114 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

probably be so far able to localize the seat of irrita-
tion as to confine its movements, in its search for the
offending body, to perhaps the quadrant of the bell
in which the stimulation is being applied. If the
stimulation be now supplied at e, the localization
on the part of the manubrium will be still more
accurate ; and if applied at /(that is, almost beneath
one end of the cut A B), the manubrium may suc-
ceed in localizing quite correctly.

These facts may also be well brought out by
another mode of section, viz. by cutting round a
greater or less extent of the marginal tissue, leaving
one end of the resulting slip free, and the other end
attached in situ. If this form of section be
practised on Tiaropsis indicans, as represented at
g k in the figure, it may also be observed that
irritation of a distant point in the marginal strip,
such as g or h, causes the manubrium to move in
various directions, without any special reference to
that part of the bell which the irritated point of
the marginal strip would occupy if in situ. But if
the stimulation be applied only one or two millims.
from the point of attachment of the marginal strip,
as at i, the manubrium will confine its localizinof
motions to perhaps the proper quadrant of the bell ;
and if the stimulus be applied still nearer to the
attachment of the severed strip, as at^', the localizing
motions of the manubrium may become quite
accurate.

Asrain, wdth reirard to radial distance, if the cut
A B in the figure were situated higher up in the
bell, as at A' B', and the arc, c, d, e, f, of the

SECTION OF NAKED-EYED MEDUSA. 115

margin irritated as before, the manubrium would
be able to localize better than if, as before, the
radial distance between A B and c, d, e, f were less.
The greater this radial distance, the better would
be the localizing power of the manubrium ; so that,
for instance, if the cut A' B' were situated nearly
at the base of the manubrium, the latter orofan
might be able to localize correctly a stimulus ap-
plied, not only as before at /, but also at e or d. In
such comparative experiments, however, it is to be
understood that the higher up in the bell a cut is
placed, the shorter it must be ; for a fair comparison
requires that the two ends of the cut shall always
touch the same two radii of the nectocalyx. Still,
if the cut is only a very short one (say one or two
millims. long), this consideration need not practically
be taken into account ; for such a cut, if situated
just above the margin, as represented at a, will
have the effect of destroying the localizing power of
the manubrium as regards the corresponding arc of
the margin; but if situated high up in the bell,
even though its length be still the same, it will not
have this effect.

From all this, then, we have seen that the con-
nections which render possible the accurate localiz-
ino^ functions of the manubrium are almost, though
not quite, exclusively radial. We have also seen
that between accurate localization and mere random
movements on the part of the manubrium there are
numerous gradations, the degree of decline from
one to the other depending on the topographical
relations between the point of stimulation and the

IIG JELLY-FISH, STAR-FISTI, AND SEA-URCHINS.

end of the section (the section being of the form
represented by A B in the figure). These relations,
as we have seen, are the more favourable to correct
localization : (a) the greater the radial distance be-
tween the point of stimulation and the end of the
section ; and (6) the less the circumferential distance
between the point of the stimulation and the radius
let fall from the end of the section. But we have
seen that the limits as regards severity of section
within which these gradations of localizing ability
occur, are exceedingly restricted — a cut of only a
few millims. in length, even though situated at the
greatest radial distance possible, being sufficient to
destroy all localizing power of the manubrium as
regards the middle point of the corresponding arc
of the margin, and a stimulus applied only a
few millims. from the attached end of a severed
marginal strip entirely failing to cause localizing
action of the manubrium. Lastly, we have seen
that even after all localizing action of the manu-
brium has been completely destroyed by section of
the kinds described, this organ nevertheless con-
tinues actively, though inefiectually, to search for
the seat of irritation.

The last-mentioned fact shows that after excita-
tional continuity of a higher order has been
destroyed, excitational continuity of a lower order
nevertheless persists ; or, to state the case in
other words, the fact in question shows that after
severance of the almost exclusively radial connec-
tions between the bell and the manubrium, by
which the perfect or unimpaired localizing function

SKCTION OF NAKKD-EYED MEDUSAE

117

of the latter is rendered pussible, other coiineetions
between these or^^ans remain wliich are not in any
wi.se radial. 1 therefore next tested the degree in
which these non-radial connections might be cut
without causing destruction of that excitational
continuity of a lower order which it is their func-
tion to maintain. It will here suffice to record one
mode of section Avhich has yielded definite results.
A glance at the accompanying illustration (Fig. 23)
will show the manner in which the Medusa is pre-

Fig 23.

pared. The margin having been removed (in order to
prevent possible conduction by the marginal nerve-
fibres), a single deep radial cut (a a) is first made, and
then a circumferential cut (a, h, c) is carried nearly
all the way round the base of the manubrium. In
this way the nectocalyx, deprived of its margin, is
converted into a continuous band of tissue, one of
the ends of which supports the manubrium. Now
it is obvious that this mode of section must be very
trying to nervous connections of any kind subsist-

118 JELLY-FISH, STAR-FISII, AND SEA-URCHINS.

ing between the bell and the manubrium. Never-
theless, in many cases, irritating any part of the
band a I has the effect of causing the manubrium
to perform the active random motions previously
described. In such cases, however, it is observable
that the further away from the manubiium the
stimulus is applied, the less active is the response
of this organ. In very many instances, indeed, the
manubrium altogether fails to respond to stimuli
applied at more than a certain distance from itself.
For example, referring to Fig. 23, the manubrium
might actively respond to irritation of any point
in the division d, e, /, g, w^hile to irritation of any
point in the division /, g, h, i its responses would
be weaker, and to irritation of any point in //, i, j, k,
they would be very uncertain or altogether absent.
Hence in this form of section we have reached
about the limit of tolerance of which the non- radial
connections between the bell and manubrium are
capable.

Another interesting fact brought out by this form
of section is, that the radial tubes are tracts of
comparatively high irritability as regards the manu-
brium ; for the certainty and vigour with which
the manubrium responds to a stimidus aoplied at
one of the severed radial tubes, /, g, or h, i, or j, k,
contrast strongly with the uncertainty and feeble-
ness with which it often responds to stimuli applied
between any of these tubes. Indeed, it frequently
happens that a specimen which will not respond
at all to a stimulus applied between two radial
tubes, will respond at once to a stimulus applied

SECTION OF xNAKED-EVED MEDUS.E. 119

much fiirtlier from tlie manubrium, but in the course
of the radial tube /A;.

And til is leads us to another point of interest.
In such a form of section, when any part of the
mutilated nectocalyx is irritated, the manubrium
shows a very marked tendency to toucli some point
in the tissue-mass a a d e (Fig. 23) by which it still
remains in connection with the bell, and throuirh
which, therefore, the stimulus must pass in order
to reach the manubrium. And it is observable that
this tendency is particularly well marked if the
section has been planned as represented in Fig. 23,
i.e. in such a way as to leave the tissue-tract a a d e
pervaded by a nutrient-tube d e, this tube being
thus left intact. When this is done, the manubrium
most usuall}^ points to the uninjured nutrient-tube
d e every time any part of the tissue-band a Z is
irritated.

Let us now very briefly consider the inferences
to which these results would seem to point. The
fact that the localizing power of the manubrium
is completely destroyed as regards all parts of the
bell lying beyond an incision in the latter, con-
clusively proves, as already stated, that all parts
of the bell are pervaded by radial lines of differen-
tiated tissue, which have at least for one of their
functions the conveying of impressions to the manu-
brium. The fact in question also proves that the
particular effect which is produced on the manu-
brium by stimulating any one of these lines cannot
be so produced by stimulating any of the other
lines. But althoufrh these tracts of differentiated

120 JELLY-FISH, STAK-FLSH, AND SEA-URCHINS,

tissue thus far resemble afferent nerves in their
function, we soon see that in one important par-
ticular they differ widely from such nerves; for
we have seen that, after they have been divided,
stimulation of their peripheral parts still continues
to be transmitted to their central parts, as shown
by the non-localizing movements of the manubrium.
Of course this transmission cannot take place
through the divided tissue-tracts themselves; and
hence the only hypothesis we can frame to account
for the fact of its occurrence is that which would
suppose these tissue-tracts, or afferent lines, to be
capable of vicarious action. Such vicarious action
would probably be efiected by means of intercom-
municating fibres, the directions of w^hich would
probably be various. In this way we arrive at the
hypothesis of the whole contractile sheet being
pervaded by an intimate plexus of functionally
differentiated tissue, the constituent elements of
which are capable of a vicarious action in a high
degree.

Now we know from histological observation that
there is a plexus of nerve-fibres pervading the whole
expanse of the contractile sheet, and therefore we
may conclude that this is the tissue through which
the effects are produced. But, if so, we must
further conclude that the fibres of this nerve-plexus
are capable of vicarious action in the high degree
which I have explained.

And this hypothesis, besides being recommended
by the consideration that it is the only one avail-
able, is confirmed by the fact that the stimuli which

SECTION OF NAKED-EYED MEDUSiE. 121

it supposes to escape from a severed phalanx of
nerve-fibres, and then to reach the manubrium after
being diffused through many or all of the other
radial lines (such stimuli thus converging from
many directions), are responded to when they reach
the manubrium, not by any decided localizing action
on the part of the latter, but, as the hypothesis
would lead us to expect, by the tentative and
apparently random motions which are actually
observed. Moreover, we must not neglect to notice
that these tentative or random movements resemble
in every way the localizing movements, save only
in their want of precision. Again, this hypothesis
is rendered more probable by the occurrence of
those gradations in the localizing power of the
manubrium which we have seen to be so well
marked under certain conditions. The occurrence
of such gradations under the conditions I have
named is what the theory would lead us to expect,
because the closer beneath a section that a stimulus
is applied, the greater must be the immediate lateral
spread of the stimulus through the plexus before it
reaches the manubrium. Similarly, the further the
circumferential distance from the nearest end of such
a section that the stimulus is applied, the greater will
be its lateral spread before reaching the manubrium.
Lastly, the present hypothesis would further lead
us to anticipate the fact that when Tiaropsis in-
dicans is prepared as represented in Fig. 23, the
manubrium refers a stimulus applied anywhere in
the mutilated nectocalyx to the band of tissue by
which it is still left in connection with that organ ;

122 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

for it is evident that, according to the hypothesis,
the radial fibres occupying such a band are the only
ones whose irritation the manubrium is able to
perceive, and hence it is to be expected that it
should tend to refer to these particular fibres a
source of irritation occurring anywhere in the
mutilated bell.

It is not quite so easy to understand why, in the
last-mentioned experiment, the manubrium should
tend to refer a seat of irritation to the unsevered
nutrient tube, or nerve-trunk, rather than to the
unsevered nerves in the general nerve-plexus on
either side of that nerve-trunk ; for if this nerve-
trunk at all resembles in its functions the nerve-
trunks of higher animals, the afferent elements
collected in it ought to communicate to the manu-
brium the impression of having had their distal
terminations irritated, and therefore the fact of
a number of such elements beincr collected into a
single trunk ought not to cause the manubrium to
refer a distant seat of irritation to that trunk rather
than to any of the parts from which the plexus-
elements may emanate. Concerning this difficulty,
however, I may observe that we seem to have in
it one of those cases in which it would be very un-
safe to argue, with any confidence, from the highly
integrated nervous systems with which we are best
acquainted, to the primitive nervous systems with
which we are now concerned. And although it
would occupy too much space to enter into a dis-
cussion of this subject, I may further observe that
I think it is not at all improbable that the manu-

SECTION OF NAKED EYED MEDUSA. 123

brium of Tiaropsis indicans should, in the absence
of more definite information, refer a distant seat
of injury to that tract of collected afferent elements
through which it actually receives the strongest
stimulation.

Staurophoi'a Laciniata.

Tliis is a Medusa about the size of a small saucer
which responds to stimulation of its marginal
ganglia, or radial nerve-trunks, by a peculiar
spasmodic movement. This consists in a sudden
and violent contraction of the entire muscle-sheet,
the effect of which is to draw together all the
gelatinous walls of the nectocalyx in a far more
powerful manner than occurs during ordinary swim-
ming. In consequence of this spasmodic action
being so strong, the nectocalyx undergoes a change
in form of a very marked and distinctive character.
The corners of the four radial tubes, being occupied
by comparatively resisting tissue, are not so much
affected by the spasm as are other parts of the bell ;
and they therefore constitute a sort of framework
upon which the rest of the bell contracts, the
whole bell thus assuming the form of an almost
perfect square, with each side presenting a slight
concavity inwards. These spasmodic movements,
however, are quite unmistakable when they occur
even in a very minute portion of detached tissue ; for,
however large or small the portion may be, when
in a spasm it folds upon itself with the characteris-
tically strong and persistent contraction. I say

124 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

persistent contraction, becaitae a spasmodic con-
traction, besides beinof of unusual strencrth, is also
of unusual duration ; that is to say, while an
ordinary systolic movement only lasts a short time,
a spasm lasts from six to ten seconds or more, and
this whether it occurs in a large or in a small piece
of tissue. Ag^ain, the diastolic movements differ
very much in the case of an ordinary locomotor
contraction and in that of a spasm ; for while in
the former case the process of relaxation is rapid
even to suddenness, in the latter it is exceedingly
prolonged and gradual, occupying some four or five
seconds in its execution, and, from its slow but
continuous nature, presenting a graceful appearance.
Lastly, the difference between the two kinds of
contraction is shown by the fact that, while a spasm
is gradually passing off the ordinary rhythmical
contractions may often be seen to be superimposed
on it — both kinds of contraction being thus present
in the same tissue at the same time.

Now the point with which we shall be especially
concerned is, that it is only stimulation of certain
parts of the organism which has the effect of throw-
ing it into a spasm. These parts are the margin
(including the tentacles) and the courses of the
four radial tubes (including the manubrium, which
in this species is spread over the radial tubes).
This limitation, however, is not invariable ; for I
have often seen individuals of this species respond
with a spasm to irritation of the general contractile
tissue. Nevertheless, such response to snch stimu-
lation in the case of this species is exceptional —

SECTION OF NAKED-EYED MEDUSAE. 125

the usual response to muscular irritation being an
ordinary locomotor contraction, which forms a
marked contrast to the tonic spasm that invariably
ensues upon stimulation of the margin, and almost
invariably upon the stimulation of a radial tube.

The first question I undertook to answer was the
amount of section which the excitable tissues of
Staurophora laciniata would endure without losing
their power of conducting the spasmodic contraction
from one of their parts to another. This was a
very interesting question to settle, because Stauro-
phora laciniata, like all the other species of disco-
phorus naked-eyed Medusre, differs from Aurelia,
etc., in that the ordinary contraction- waves are very
easily blocked by section. It therefore became in-
teresting to ascertain whether or not the wave of
spasm admitted of being blocked as easily. First,
then, as regard* the margin. If this be all cut off in
a continuous strip, with the exception of one end
left attached in situ, irritation of any part of the
almost severed strip will cause a responsive spasm
of the bell, so soon as the wave of stimulation has
time to reach the latter. I next continued this form
of section into the contractile tissues themselves,
carrying the incision round and round the bell in
the form of a spiral, as represented in the case of
Aurelia by Fig. 11, page 70. In this way I con-
verted the whole Medusa into a ribbon-shaped piece
of tissue ; * and on now stimulating the marginal

* It may be stated that while conducting this mode of section
of Staurophora laciniata, the animal responds to each cut of the
contractile tissues with a locomotor contraction (or it may not

126 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

tissue at one end of the ribbon, a portion of the
latter would go into a spasm. The object of this
experiment was to ascertain how far into the
ribbon-shaped tissue the wave of spasm would
penetrate. As I had expected, different specimens
manifested considerable differences in this respect,
but in all cases the degree of penetration was
astonishingly great. For it was the exception to
find cases in which the wave of spasm failed to
penetrate from end to end of a spiral strip caused
by a section that had been carried twice round the
nectocalyx ; and this is very astonishing when we
remember that the ordinary contraction-waves,
whether originated by stimulation of the contractile
tissues or arising spontaneously from the point of
attachment of the marginal strip, usually failed to
penetrate further than a quarter of the way round.
Moreover, these waves of spasm will continue to
penetrate such a spiral strip even after the latter
has been submitted to a system of interdigitating
cuts of a very severe description.

Now, we have here to deal with a class of facts
which physiologists will recognize as of a perfectly
novel character. Why it should be that the very
tenuous tracts of tissue which I have named should
have the property of responding even to a feeble
stimulus by issuing an impulse of a kind which
throws the contractile tissues into a spasm ; why it
should be that a spasm, when so originated, should

respond at all) ; but each time the section crosses one of the
radial tubes, the whole bell in front of the section, and the whole
strip behind it, immediately go into a spasm.

SECTION OF NAKED-EYED MEDUSAE. 127

manifest a power of penetration to which the
normal contractions of the tissues in which it occurs
bear so small a proportion ; why it is that the con-
tractile tissues should be so deficient in the power of
originating a spasm, even in response to the strongest
stimulation applied to themselves ; — these and other
questions at once suggest themselves as cpiestions of
interest. At present, however, I am wholly unable
to answer them ; though we may, I think, fairly
assume that it is the ganglionic element in the
margin, and probably also in the radial tubes,
which responds to direct stimulation by discharging
a peculiar impulse, which has the remarkable effect
in question. I'or the sake of rendering the matter
quite clear, let us employ a somewhat far-fetched
but convenient metaphor. We may compare the
general contractile tissues of this Medusa to a mass
of gun-cotton, which responds to ignition (direct
stimulation) by burning with a quiet flame, but to
detonation (marginal stimulation) with an explosion.
In the tissue, as in the cotton, every fibre appears
to be endowed with the capacity of liberating
energy in either of two very different ways ; and
whenever one part of the mass is made, by the ap-
propriate stimulus, to liberate its energy in one of
these two ways, all other parts of the mass do the
same, and this no matter how far through the
mass the liberating process may have to extend.
Now, employing this metaphor, what we find is
that, while the contractile fibres resemble the cotton
fibres in the respects just mentioned, the ganglion
cells resemble detonators, when themselves directly

128 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

stimulated. In other words, the ganglion-cells of
this Medusa are able to originate two very different
kinds of impulse, according as they liberate their
energy spontaneously or in answer to direct stimu-
lation, and the muscular tissues respond with a
totally ditferent kind of contraction in the two
cases. Possibly, indeed, direct stimulation of the
ganglia is followed by a spasm of the muscular
tissue only because a greater amount of ordinary
ganglion intiuence is thus liberated than in the case
of a merely spontaneous discharge. If this were
the explanation, however, I should not expect so
great a contrast as there is between the facility
with which a spasm may be caused by stimulation
of the margin and of the contractile tissue respec-
tively. The slightest nip of the margin of Stauro-
phora laciniata, for instance, is sufficient to cause
a spasm, whereas even crushing the contractile
tissues with a large pair of dissecting-forceps Avill
probably fail to cause anything other than an
ordinary contraction. Nevertheless, pricking the
margin with a fine needle usually has the effect of
causing only a locomotor contraction.

In conclusion, I may state that amesthetics have
the effect of blocking the spasmodic wave in any
portion of tissue that is submitted to their in-
fluence. It is always observable, however, that
this effect is not produced till after spontaneity has
been fully suspended, and even muscular irritability
destroyed as regards direct stimulation. Up to
this stage the certainty and vigour of the spasm
consequent on marginal irritation are not per-

SECTION OF NAKED-EYED MEDUSAE. 129

ceptibly impaired ; but soon after this stage the
intensity of the spasm begins to become less, and
later still it assumes a local character. It is im-
portant, also, to notice that at this stage the effect
of marginal stimulation is ver}^ often that of pro-
ducing a general locomotor contraction, and some-
times a series of two or three such. During recovery
in normal sea-water all these phases occur in
reverse order.

CHAPTER VI.

CO-ORDINATION.

Covered-eyed MeduscB.

From the fact that in tlie covered-eyed Medussethe
passage of a stimulus-wave is not more rapid than
that of a contraction-wave, we may be prepared
to expect that in these animals the action of the
locomotor ganglia is not, in any proper sense of the
term, a co-ordinated action ; for if a stimulus- wave
cannot outrun a contraction-wave, one ganglion
cannot know that another ganglion has discharged
its influence till the contraction-wave, which re-
sults from a dischar^je of the active o^anHion, has
reached the passive one. And this I find to be
generally the case ; for it may usually be observed
that one or more of the lithocysts are either tempo-
rarily or permanently prepotent over the others,
i.e. that contraction-waves emanate from the pre-
potent lithocysts, and then spread rapidly over
the swimming-bell, without there being any signs of
co-ordinated or simultaneous action on the part of
the other lithocysts. Nevertheless, in many cases
such prepotency cannot, even with the greatest
care, be observed; but upon every pulsation all

CO-ORDINATION. 131

parts of the swimming-bell seem to contract at the
same instant. And this apparently perfect co-
ordination amono- the eiii'ht marginal o-ano'lia mav

O O O O O V

continue for any length of time. I believe, however,
that such apparently complete physiological har-
mony is not co-ordination properly so called, i.e. is
not due to special nervous connections between the
ganglia ; for, if such were the case, perfectly syn-
chronous action of this kind ought to be the rule
rather than the exception.

I am therefore inclined to account for these cases
of perfectly synchronous action by supposing that
all, or most, of the ganglia require exactly the same
time for their nutrition ; that they are, further, of
exactly equal potency in relation to the resistance
(or excitability) of the surrounding contractile
tissues ; and that, therefore, the balance of forces
being exactly equal in the case of all, or most, of the
ganglia, their rhythm, though perfectly identical, is
really independent. I confess, however, that I am
by no means certain regarding the accuracy of this
conclusion, as it is founded on negative rather than
on positive considerations : that is to say, I arrive
at this conclusion regarding the cases in which such
apparent co-ordination is observable only because
in other cases such apparent co-ordination is not
observable ; and also, I may add, because my
experiments in section have not revealed any
evidence of nervous connections capable of con-
ducting a stimulus-wave with greater rapidity than
a contraction-wave. I therefore consider this con-
clusion an uncertain one, and its uncertainty is,

132 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

perhaps, still further increased by the result of the
following experiments.

If a covered-eyed Medusa be chosen in which
perfectly synchronous action of the ganglia is
o))servable, and if a deep radial incision be made
between each pair of adjacent ganglia — the incisions
beinof thus eiijht in number and carried either from
the margin towards the centre or vice versa — it
then becomes conspicuous enough that the eight
partially divided segments no longer present syn-
chronous action ; for now one segment and now
another takes the initiative in starting a contraction-
wave, which is then propagated to the other
seofments. And it is evident that this fact tends to
negative the above explanation, for if the discharges
of the ganglia are independently simultaneous
before section, we might expect them to continue so
after section. It must be remembered, however,
that the form of section we are considering is a
severe one, and that it must therefore not only give
rise to general shock, but also greatly interfere with
the passage of contraction-waves, and, in general,
disturb the delicate conditions on which, according
to the suggested explanation, the previous harmony
depended. Besides, as we shall subsequently see,
for some reason or other segmentation of a Medusa
profoundly modifies the rate of its rhythm. In
view of these considerations, therefore, the results
yielded by such experiments must not be regarded
as having any conclusive bearing on the question
before us ; and as these or similar objections
apply to various other modes of section by which

CO-OllDINATION. 138

I have endeavoured to settle this question, I will
not here occupy space in detailing them.

It seems desirable, however, in this connection
again to mention a fact briefly stated in a former
chapter, namely, that section conclusively proves
a contraction-wave to have the power, when it
reaches a lithocyst, of stimulating the latter into
activity ; for it is not difficult to obtain a series
of lithocysts connected in such a manner that the
resistance offered to the passage of the waves by
a certain width of the junction-tissue, is such as
just to allow the residuum of the contraction- wave
which emanates from one lithocyst to reach the
adjacent lithocyst, thus causing it to originate
another wave, wdiich, in turn, is just able to pass to
the next lithocyst in the series, and so on, each
lithocyst in turn acting like a reinforcing battery
to the passage of the contraction- wave. Now this
fact, I think, sufficiently explains the mechanism of
ganglionic action in those cases where one or more
lithocysts are prepotent over the others ; that is to
say, the prepotent lithocyst first originates a con-
traction-wave, which is then successively reinforced
by all the other lithocysts during its passage round
the swimming-bell. In this way the passage of
a contraction-wave is no doubt somewhat accele-
rated ; for I found, in marginal strips, that the rate
of transit from a terminal lithocyst to the other
end of the strip was somewhat lowered by excising
the seven intermediate lithocysts.

I may here state, in passing, a point of some
little interest in connection with this reinforcing
10

134 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

action of litliocjsts. When I first observed this
action, it appeared to me a mysterious thing why
its result was alwa^^s to propagate the contraction-
wave in only one direction — the direction, namely,
in which the wave happened to be ]mssing before it
reached the lithocyst. For instance, suppose we
have a strip A D, Avith a lithocyst at each of the
equidistant points A, B, C, D ; and suppose that the
lithocyst B originates a stimulus : the resulting
contraction- wave passes, of course, with equal
rapidity in the two opposite directions, B A, B C
(arrov/s h a, h c) : the contraction- wave h a therefore

F'-. 24.

reaches the lithocyst A at the snme time as the
contraction-wave b c reaches the lithocyst C, and
so both A and C discharge simultaneously. What,
then, should we expect to be the result ? I think
we should expect the wave b c to continue on its
course to D, alter having been strengthened at C,
and a reflex wave a' V to start from A (owing to
the discharge at A), which would reach B at the
same time as a similar reflex wave c' V starting
from C (owing to the discharge at C) ; so that by
the time the original wave b c d had reached D,
the point B would be the seat of a collision between
the two reflex waves a' b' and c' <V . And, not to

CO-ORDINATION. 135

push the supposed case further, it is evident that
if such reflex waves were to occur, the resultincr
confusion would very soon require to end in tetanus.
As a matter of fact, these reflex waves do not occur ;
and the question is, why do they not ? Why is it
that a wave is 6nly reinforced in the direction in
which it happens to be travelling — so that if, for
instance, it happens to start from A in the above
series, it is successively propagated by B C in the
direction A, B, C, D, and in that direction only ;
whereas, if it happens to start from D, it is propa-
gated by the same lithocysts in the opposite
direction, D, C, B, A, and in that direction only — the
wave in the one case terminating at the lithocyst D,
and in the other case at the lithocyst A ? Now,
although this absence of reflex waves appears at
first sight mysterious, it admits of an exceedingly
simple explanation. I find that the contractile
tissues of the covered-eyed Medusae cannot be made
to respond to two successive stimuli of minimal, or
but slightly more than minimal intensity, unless
such stimuli are separated from one another by
a certain considerable interval of time. Now, when
in the above illustration the contraction- wave starts
from A, by the time it reaches B the portion of
tissue included between A and B has just been in
contraction in response to the stimulus from A,
while the portion of tissue included between B and
C has not been in contraction. Consequently,
the stimulus resulting from a ganglionic discharge
being presumably of minimal, or but slightly more
than minimal intensity, the tissue included be-

186 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

tween A and B will not respond to tlie discharge
of B ; while the tissue included between B and C,
not having been just previously in contraction,
will respond. And conversely, of course, if the con-
traction-wave had been travelling in the opposite
direction.

Seeing that this explanation is the only one
possible, and that it moreover follows as a deduc-
tive necessity from my experiments on stimulation,
I think there is no need to detail any of the further
experiments which I made with the view of con-
firming it. But the following experiment, devised
to confirm this explanation, is of interest in itself,
and on this account I shall state it. Having pre-
pared a contractile strip with a single remaining
lithocyst at one end, I noted the rhythm exhibited
by this lithocyst, and then imitated that rhythm
by means of single induced shocks thrown in with
a key at the other end of the strip. The eftect of
these shocks was, of course, to cause the contraction-
weaves to pass in the direction opposite to that in
which they passed when originated by the litho-
cyst. Now I found, as I had expected, that so long
as I continued exactly to imitate the rate of gang-
lionic rhythm, so long did the waves always pass
in the direction B A — A being the lithocyst, and B
the other end of the strip. I also found that if I
allowed the rate of the artificially caused rhythm
to sink slightly below that of the natural rhythm,
after every one to six waves (the number depend-
ing on the degree in which the rate of succession of
my induction shocks approximated to the rate of

CO-ORDINATION. 137

the natural rhythm) which passed from B to A, one
would pass from A to B.*

Of course the only interpretation to be put on
these facts is that every time an artificially started
wave reached the terminal ganglion it caused tlie
latter to discharge; but that the occurrence of a
discharge could not in this case be rendered ap-
parent, because of the inadequacy of that discharge
to start a reflex wave. But that such discharges
always took place was manifest, both d priori be-
cause from analogy we may be sure that if there
had happened to be any contractile tissue of appro-
priate width on the other side of the ganglion, the
discharge of the latter would have been rendered
apparent, and d posteriori because, after the arrival
of every artificially started wave, the time required
for the ganglion to originate another wave was pre-
cisely the same as if it had itself originated the
previous wave.

In view of these results, it occurred to me as an
interesting experiment to try the effect on the
natural rhythm of exhausting a ganglion thus situ-
ated, by throwing in a great number of shocks at
the other end of the strip. I found that after five
hundred single shocks had been thrown in with a
rapidity almost sufiicient to tetanize the strip, im-
mediately after the stimulation ceased, the natural

* When two such waves met, they neutralized each other at
their line of collision ; or perhaps more correctly, the tissue on
each side of that line, having just been in contraction, was not
able again to convey a contraction- wave passing in the oppo-
site direction to the wave which it had conveyed immediately
before.

lo8 JELLY-FISH, STAll-FISH, AND SEA-URCHINS.

rhythm of the ganglion, which had previously been
twenty in the minute, fell to fourteen for the first
minute, eicfhteen for the second, and the orio-iiKil
rate of twenty for the third. In such experiments
the diminution of rate is most conspicuous during
the first fifteen or thirty seconds of the first minute.
Sometimes there are no contractions at all for the
first fifteen seconds after cessation of the stimulatina:
process, and in such cases the natural rhythm,
when it first begins, may be as slow as one-half or
even one-quarter its normal rate. All these effects
admit of being produced equally well, and with less
trouble, by faradizing the strip, when it may be
even better observed how prolonged may be the
stimulation, without causing anything further than
such slight exhaustion of the ganglion as the above
results imply.*

Kaked-eyed Medusce.

It would be impossible to imagine movements on
the part of so simple an organism more indicative
of physiological harmony than are the movements
of Sarsia. One may watch several hundreds of
these animals while they are swimming about in
the same bell-jar and never perceive, as in the
covered-eyed MedusMe, the slightest want of gang-

* In this description I have everywhei-e adopted the current
phraseology with regard to ganglionic action — a phi-aseology
which embodies the theory of ganglia supplying interrupted stimu-
lation. But although I have done this for the sake of clearness,
of course it will be seen that the facts harmonize equally well
with the theoi-y of continuous stimulation, to which 1 shall alludo
further on.

CO-OKDINATION. 139

lionic co-ordination exhibited by any of the speci-
mens. Moreover, that the ganglionic co-ordination
is in this case wonderfully far advanced is proved
by the fact of members of this genus being able
to steer themselves while following a light, as
previously described.*

In the discophorous species of naked-eyed Medusae,
however, perfectly co-ordinated action is by no
means of such invariable occurrence as it is in
Sarsia; for although in perfectly healthy and
vigorous specimens systole and diastole occur at
the same instant over the whole nectocalyx, this
harmoniously acting mechanism is ver}^ liable to be
thrown out of gear, so that when the animals are
suffering in the least degree from any injurious
conditions, often too slio'ht and obscure to admit of
discernment, the swimming movements are no longer
synchronous over the whole nectocalyx; but now
one part is in systole while another part is in
diastole, and now several parts may be in diastole
while other parts are in systole. And as in these
animals very slight causes seem sufficient thus to
impair the ganglionic co-ordination, it generally
happens that in a bell-jar containing a number of
specimens belonging to different species, numerous
examples of more or less irregular swimming move-
ments are observable.

Taking, then, the case of Sarsia first, from my

* Removing the mannbrinm does not interfere with this steerin^j
action ; bat if any considerable portion of the margin is excised,
the animal seems no longer able to find the beam of light, even
though one or more of the marginal bodies be left iyi situ.

140 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

previous observations on the physiological harmony
subsisting between the tentacles, I was led to expect
that the co-ordination of the locomotor ganglia w^as
probably effected by means of the same tissue-tracts
through Avhich the intertentacular harmony was
effected, namely, those situated in the margin of the
bell. Accordingly, I introduced four short radial
cuts, one midway between each pair of adjacent
inariiinal bodies. The co-ordination, how^ever, was
not perceptibly impaired. I therefore continued
the radial cuts, and found that when these reached
one-half or two-thirds of the way up the sides of
the inner bell (or contractile sheet), the co-ordina-
tion became visibly affected, and this for the first
time.

I also tried the following experiment. Instead
of beginning the radial cuts from the margin, I
began them from the apex of the cone ; and I found
that however many of such cuts I introduced, and
however far down the cone I carried them, so long
as I did not actually sever the margin, so long did
all the divisions of the bell continue to contract
simultaneously.* This fact, therefore, proves that
the marofin of the bell is alone sufficient to maintain
co-ordination,

* This could be pnrticalarly well seen if, after the extreme
apex of the cone had been removed, one of the four radial cuts
was continued through the margin, and the latter was then
spread out into a linear form by gently pressing the animal against
the flat side of the glass vessel in which it was contained. The
same experiment performed on Aurelia is, of course, attended
with a totally different result, now one segment and now another
oiii^inating a discharge which then spreads to all the others in
the form of a contraction-wave.

CO-ORDINATION. 141

The next experiment I tried was to make four
short radial incisions in the margin as before
described, and then to continue one of these in-
cisions the Avhole way up the bell. By careful
observation I could now perceive that all the
marginal ganglia did not discharge simultane-
ously ; for when those situated nearest to the long
radial cut happened to take the initiative, the
resulting contraction- wave, having double the dis-
tance to travel which it would have had if the long
radial cut had been absent, could now be followed
by the eye in its very rapid course round the bell.
Now, the fact that in this form of section I was
able to detect the passage of a wave, proves that
the three short radial sections had destroyed the
co-ordinated action of the marginal ganglia.

From these experiments, then, I conclude that in
this genus ganglionic co-ordination, in the strict
sense of the term, is effected exclusively by means
of the marginal nerves. And as these experiment*^
on Sarsia are exceedingly difficult to conduct, owing
to the very rapid passage of contraction-waves in
this genus, it is satisfactory to find that this con-
clusion is further supported by the analogy which
the other species of naked-eyed Medusre afford, and
to the consideration of which we shall now proceed.

The effects of four short radial incisions through
the margin of any species of Tiaropsis, Thaumantias,
Staurophora, etc., are usuall}^ very conspicuous.
Each of the quadrants included between two adjacent
incisions shows a strong tendency to assume an
independent action of its own. This tendency is

142 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

sometimes so pronounced as to amount almost to
a total destruction of contractional continuity
between two or more quadrants of tlie bell ; but
more usually the effect of the marginal sections is
merely that of destroying excitational continuity,
or at least physiological harmony.

It is an interesting thing that this form of section,
although in actual amount so very slight, is attended
with a much more pernicious influence on the
vitality of the organism than is any amount of
section of the general contractile tissues. Thus, if
a specimen of Tiaropsis, for example, be chosen
which is swimming about with the utmost vigour,
and if four equidistant radial cuts only just long
enough to sever the marginal canal be made, the
animal will soon begin to show symptoms of enfeeble-
ment, and within an hour or two after the operation
will probably have ceased its swimming motions
altogether. The animal, however, is not actually
dead ; for if while lying motionless at the bottom of
the vessel it be gently stimulated, it will respond
with a spasm as usual, and perhaps immediately
afterwards give a short and feeble bout of swimming
movements. These surprisingly pernicious results
are not so conspicuous in the case of Sarsia, although
in this genus likewise they are sufficiently well
marked to be unmistakable. I here append a table
to show the comparative effects of the operation in
question on different species. The cases may be
regarded as very usual ones, though it often happens
that a longer time after the operation must elapse
before the enfeebling effects become so pronounced.

CO-OllDINxVTION.

14:3

Name of speciis.

Nnmbor of
cuiitr.ictions
during five

niiiiutes
be. ore opera-
tion.

Nunib?r
(iurinf? one

iiiiiiiiie

ait r

opoiation.

Number
during tive

minutes

after

operation.

Ultlnate
elfeits.

Tiaropsis diailemata

■ indioaiKs

pf>l_v(lia(lc'iii!ita

olii::()l)l(»<aiua

Saisia tubalosa ...

57
MS
102

1:51
141

11

23

18
39
56

0

0

0

0

H

Permanent
rest.

This decided effect of so slight a mutilation will
not, perhaps, appear to other physiologists so note-
worthy as it appears to me ; for no one who has
not witnessed the experiments can form an
adequate idea of the amount of mutilation of any
parts, other than their margins, which the Medusa?
will endure without even suffering from the effects
of shock. Another point worth mentioning with
regard to the operation we are considering is, that
not un frequently the interruptions of the margin,
which have been produced artificially, begin to
extend themselves through the nectocalyx in a
radial direction ; so that in some cases this organ
becomes spontaneously segmented into four quad-
rants, which remain connected only by the apical
tissue of the bell. I do not think that this is due
to the mere mechanical tearing of the tissues as
a consequence of the swimming motions, for the
latter seem too feeble to admit of their pi'oducing
such an effect.

In conclusion, I may state that 1 have been able
temporarily to destroy the ganglionic co-ordination

144 JELLY-FISK, STAR-FISH, AND SEA-URCHINS.

of SarsitC, by submitting the animals to severe
nervous sliock. The method I employed to pro-
duce the nervous shock, without causing mutilation,
was to take the animal out of the water for a few
seconds while I laid it on a small anvil, which I
then struck violently with a hammer. On imme-
diately afterwards restoring the Medusa to sea-
water, spontaneity was found to have ceased, while
irritability remained. After a time spontaneity
began to return, and its first stages were marked
by a complete want of co-ordination ; soon, however,
co-ordination was again restored. But this experi-
ment by no means invariably yielded the same
result. Spontaneity, indeed, was invariabl}^ sus-
pended for a time ; but its first return was not
invariably, or even generally, marked by an absence
of co-ordination, even though I had previously struck
the anvil a number of times in succession. I was
therefore led to try another method o£ producing
nervous shock, and this I found a more effectual
method than the one just described. It consisted
in violently shaking the Sarsise in a bottle half filled
with sea- water. I was surprised to find how
violent and prolonged such shaking might be with-
out any part of the apparently friable organism,
except perhaps the tentacles and manubrium, being-
broken or torn. The subsequent effects of shock
were remarkable. For some little time after their
restoration to the bell-jar, the SarsitB had lost, not
only their spontaneity, but also their irritability,
for they would not respond even to the strongest
stimulation. In the course of a few minutes, how-

CO-ORDINATION. 145

ever, periplieral irritability returned, as shown by
responses to nipping of the neuro-muscular sheet.
The animals were now in the same condition as
when amTesthesiatod by cafiein or other central
nerve-poison ; but in a few minutes later central
or reflex irritability also returned, as shown by
single responses to single nippings of the tentacles.
Last of all spontaneity began to return, and was
in some few cases conspicuously marked by a want
of co-ordination, all parts of the margin originating
impulses at different times, with the result of pro-
ducing a continuous flurried or shivering movement
of the necto calyx. After a time, however, these
movements became co-ordinated ; but in most cases
w^hen a swimming bout had ended and a pause
intervened, the next swimming bout was also in-
augurated by a period of shivering before co-ordina-
tion became established. This effect mio^ht last for
a long time, but eventually it, too, disappeared,
the swimming bouts then beginning with co-or-
dinated action in the usual way.

CHAPTER VII.

NATURAL RHYTHM.

It will be convenient here to introduce all the
observations that I have been able to make with
regard to the natural rhythm of the Medusae. As
Dr. Eimer has also made some observations in this
connection, before proceeding with the fresh points
having relation to this subject, I shall consider
those to which he alludes.

In Aurelia aurita, as Dr. Eimer noticed, the rate
of the rhythm has a tendency to bear an inverse
proportion to the size of the individual. Size, how-
ever, is far from being the only factor in determin-
ing the diiferences between the rate of the rhythm
of different specimens, the individual variations in
this respect being very great even among specimens
of the same size. What the other factors in question
may be, however, I am unable to suggest.

Dr. Eimer also affirms that the duration of the
natural pauses, which in Aurelia habitually alter-
nate with bouts of swimming, bears a direct pro-
portion to the number and strength of the contrac-
tions that occurred in the previous bout of swim-
ming. I observed that Sarsiye are much better

NATURAL RHYTHM.

147

adapted than Aureliae for determining whether any
such precise relation obtains; for, in the first place,
the strength of the contraction is more uniform,
and, in the next place, the alternation of pauses
with bouts of swimming is of a more decided
character in Sarsiae than in healthy specimens of
Aurelise. I further observed that in Sarsia no such
precise relation did obtain, although in a very
general way it is true, as might be expected, that
unusually prolonged bouts of swimming were some-
times followed by pauses of unusual duration. As
all the observations are very much the same, I shall
only quote two of them : —

Sarsia.

Sarsia (anoth

or specimen).

Number of pul-

Seconds of

Nnmbor oT pul-

Seconds of

sations.

rest.

sations.

rest.

54

90

40

GO

20

15

29

90

9

92

32

132

51

40

33

92

38

GO

18

59

1

43

8

G3

63

45

15

35

1

14

2

85

60

15

11

63

6

50

30

33

3S

50

J7

81

22

32

19

67

2.5

12

3

65

56

55

19

36

er^

20

41

123

42

15

^0

23

35

40

61

1.50

76

43

45

145

40

120

10

97

14

35

148 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

These observations may be taken as samples of
others which it would be unnecessary to quote, as
it will be seen from the above that there is no pre-
cise relation between the number of the pulsations
and the duration of the pauses. Nevertheless, thai
there is a general relation may be seen from some
cases in which unusually prolonged pauses occur.
Tlie followino: instance will serve to show this: —

Sarsia (another specimen).

Number of pulsations.

Seconds of rest.

38

30

22

35

49

40

30

45

46

20

2

15

24

380

112

20

45

185

894

30

6

45

4

140

2

185

30

210

200

60

Tn this case, the relation between the long pause of
380 seconds and tlie subsequent prolonged swim-
ming bout of 112 pulsations is obvious; also, as
the latter was then followed by a short pause of
twenty seconds and another comparatively short
bout of forty-five pulsations, the refreshing influence
of the previous 380 seconds rest may be supposed
to have been not quite neutralized by the exhausting
effect of the foregoing 112 pulsations. At any rate,
looking to the general nature of the previous pro-
portions (viz. in their sum ^jj), it is certain that
ff I leaves a large preponderance in favour of nutri-

NATUllAL KHYTIIM. 149

tion, which preponderance is not much modified
by adding the next succeeding proportion, thus,
frlris = tlT- Consequently, the organism may faiily
be supposed to have entered upon the next pro-
longed period of rest (viz. 185 seconds) with a large
balance of reserve power; so that when to this large
balance there was added the further accumulation
due to the further rest of 185 seconds, we are not
surprised to find the next succeeding swimming
bout comprising the enormous number of 894
pulsations. But this great expenditui'e of energy
seems to have been somewhat in excess of the
energy previously accumulated by the prolonged
rest, for this unusual expenditure seems next to
have entailed an unusually prolonged period of
exhaustion. At any rate, it is plainly observable
that the next succeeding proportions are greatly in
favour of repose; for it is not until 360 seconds
have elapsed, with only twelve pulsations in the
interval, that er.ergy enough has been accumulated
to cause a moderate bout of thirty pulsations. But
next another long and sustained pause of 240
seconds supervenes, and, the animal being now fully
refreshed with a large surplus of accumulated
energy, the next succeeding swimming bout com-
prises two hundred pulsations. Lastly, there suc-
ceeded sixty seconds of rest, and here the observa-
tion terminated.*

* If the reader takes the trouble to ascertain the average pro-

portiou between the number of pulsations and the seconds of rest

in the first observations as far down as the first long pause, viz.

as above stated, m, and if he then balances the succeeding income

11

150 JELLY-FISH, STAR-FISII, AND SEA-URCHINS.

Effects of Segmentation on the Rhythm.

We have next to consider Dr. Eimer's observa-
tions concerning the effects on the rhythm of
Aurelia which result on cutting the animal into
segments ; and here, again, I much regret to say
that I cannot wholly agree with this author. He
says he found evidence of a very remarkabhj fact,
viz. that by first counting the natural rhythm of an
unmutilated Aurelia, and then dividing the animal
into two halves, one of these halves into two
quarters, and one of these quarters into two eighths;
the sum of the contractions performed by these four
segments in a given time was equal to the number
which had previously been performed in a similar
time by the unmutilated animal. And not only so,
but the number of contractions which each segment
contributed to this sum was a number that stood in
direct proportion to the size of the segment; so
that the half contracted half as many times, the
quarter a quarter as many times, and the eighth
parts one-eighth part the number of times that the
unmutilated Aurelia had previously contracted in a
period of equal duration. I am glad to observe
that Dr. Eimer does not regard this rule otherwise

and expenditure of energy of all the rest of the observations, he
will find the net result to accord very precisely with the propor-
tion he previously obtained. But, as already stated, any such
precision as this is certainly the exception rather than the rule.

It may hei'e be stated that after the sixty seconds of I'est above
recorded, the animal began another swimming bout. It was then
iniQicdiately bisected, and the subsequent observations are de-
tailed in the next footnote.

NATURAL RHYTHM. 151

than as liable to frequent exception; for, as already
observed, I cannot say that my experiments have
tended to confirm it. I am only able to say that
there is general tendency for the smaller segments
of an Aurelia divided in this way to contract less
frequently than the larger segments.

It would be tedious and unnecessary to quote
any observations in this connection; but as these
observations brought out very clearly a fact which
I had previously suspected, I may detail one ex-
periment to illustrate this point. The fact in ques-
tion is, that the potency of the, lithocijsts in any
given segment of a divided Aurelia has more to do
with the frequency of its pulsations than has the
size of the segment. As previously mentioned, one
or more lithocysts may often be observed to be per-
manently prepotent over the others; and I may
here observe that the segmentation experiments
just described have shown the converse to be true,
viz. that one or more lithocysts are often per-
manently feebler than the others. Well, if a
specimen of Aurelia exhibiting decided prepotency
in one or more of its lithocysts be watched for a con-
siderable length of time, so as to be sure that the
prepotency is not of a merely temporary character,
and if the animal be then divided into segments in
such a way that the prepotent lithocysts shall
occupy the smaller segments, it may be observed,
provided time be left for the tissues to recover, that
the segments containing the prepotent lithocysts,
notwithstanding their smaller size, contract more
frequently than do the larger segments. Con-

152 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

versely, if the larger segments happen to contain
feeble lithocysts, their contractions will be but few.
I have, indeed, seen cases in which the lithocysts
appeared to be quite functionless, so far as the
origination of stimuli was concerned.

The following observations were made on a
healthy specimen of Aurelia having all its litho-
cysts in good condition but prepotency being well
marked in the case of one of them, and also, though
in a lesser degree, in the case of another. I divided
the animal so as to leave one of these two pre-
potent lithocysts in each of the eighth-part seg-
ments, and the next most powerful lithocysts in the
quadrant segment. In the following description, I
shall call the two eiglith-part segments A and B,
the former letter designating the segment contain-
ing the most powerful lithocyst. The Aurelia be-
fore being divided manifested for several hours a
very regular and sustained rhythm of thirty-two
per minute. After its division, the various segments
contracted at the following rates, in one-minute
intervals : —

Time after operation.

Segment ^.

Segment \.

Segment Jt A.

Segment J B.

1 hour.

20

25

27

15

1 „

20

25

27

15

2 hours.

29

25

27

IG

4 „

19

16

27

12

Next morning, the water which contained the
segments was somewhat foul, and this, as is always
the case, gave rise to abnormally long pauses. This
effect was much more marked in the case of some

NATURAL RHYTHM.

153

of the seorments than in that of others. I therefore
observed the segments over five-minute intervals,
instead of one- minute intervals as on the previous
day. The following is a sample of several observa-
tions, all yielding the same general result.

Segment }j.

Segment ^.

Segment | A.

Segment J B.

Number of
pulsations.

12
3

2
41
12

73

Seconds of
rest.

120
10

20

IHO

20

5 min.

No motion
duriTioftlie
hour of ob-
scrvutiun.

Continncd per-
sisteiitly to
contrdct with
a iiearlv per-
fect rhythm of
78 in 'the 5
minutes dur-
inj< the hour
of observa-
tion.

Rhythm toler-
ably perfer-l
at 78 in tiie 5
minutes ; but
this was occa-
sionally in-
terrupted by
h)ng pauses of
4 or 5 minutes'
duration.

Average late
14i per minute.

No motion.

Continuous
rhythm attlie
rote of 15 1 per
minute.

Intorruptfd
riiythiu at the
ratt! of 15 i
per minute.

I now transferred all the segments to fresh sea-
water, with the following results : —

Rhythm during first quarter of an hour immediately after trans-
ference, in five-mill ute intervals.

Time.

First 5 minutes.
Second 5 minutes
Third 5 minutes.

Segment i.

139 (irregular).

0
100 (regular).

Segment J.

0

0

39 (irregular).

Segment i A.

83 (regular).
68

Segment | B.

20 (irregular).
75 (regular).
69

Rhythm two hours after transference (five-miuute intervals).

Segment ^.

Segment \.

Segment J A.

Segment ^ B.

82 (regular).

77 regular).

70 (regular).

G2 (regular).

154f JELLY-FISH, STAR-FISH, AND SEA-URCHINa

Rliythm next day (five-minute intervals).

Segment h

Segment J.

Segment i A.

Segment | B.

G8

55

17

Dead.

Next day all the segments were dead except the
largest one, in which a single lithocyst still con-
tinued to discharge at the rate of twenty -four in
five minutes.

Now, with regard to these tables, it is to be
observed that during the first day the prepotent
lithocyst in the eighth-part segment A. maintained
an undoubted supremacy over all the others, and
that the same is true of the comparatively potent
lithocysts in the quadrant. (This is not the case
with segment B ; probably the degree of prepotency
of the lithocyst in this case was not sufficient to
counteract the antagonistic influence of the small
size of the segment.) But next day the supremacy
of the small segment A was not so marked; for
although its rhythm was more regular in the stale
water than Aras that of the largest segment, its
actual number of contractions in a given time was
just about equal to that of the largest segment.
Ao"ain, after transference to fresh sea-water, the
balance began to fall on the side of the larger seg-
ments; for even the quadrant, which in the stale
water had ceased its motions altogether, now held
a middle position between that of the half-segment
and the prepotent eighth-part segment. On the
next day, again, the balance fell decidedly in favour
ot the larger segments, and the weaker eighth-part

NATURAL RHYTHM. 155

segment died. Lastly, next day all the smaller
segments were dead.

Hence the principal facts to be gathered from
these observations are, that as time goes on the
rhythm of all the segments progressively decreases,
and that the decrease is more marked in the case of
the smaller than in that of the laro-er seirments.
This lesser endurance of the smaller seo-ments also
finds its expression in their earlier death. Now as
these smaller segments started with a greater pro-
portional amount of ganglionic power than the
laro-er se^rments, their lesser amount of endurance
can only, I think, be explained by supposing that
the process of starvation proceeds at a rate inversely
proportional to the size of the segment, a sup-
position which is rendered probable if Ave reflect
that the smaller the segment the greater is the
proportional area of severed nutrient tubes.* And

* It may be thought that the greater area of general tissue-
mass in the larger segments than in the smaller, and not the lesser
proportional area of tube-section, is the cause of the larger seg-
ments living longer than the smaller ones. I am led, however,
to reject this hypothesis, because in Sarsia, where segmentation
entails a comparatively small amount of tube-section, there is no
constant rule as to the larger segments showing more endui^ance
than the smaller ones — the converse case, in fact", being of nearly
as frequent occurrence. I can only account for this fact by sup-
posing that the endurance of the segments of Sarsia is determined
by the degree in which the three or four minute open tube-ends
become accidentally blocked. This supposition is the only one I
can think of to account for the astonishing contrasts as to en-
durance that are presented by difPerent segments of the same
individual, and, I may add, of different individuals when deprived
of their margins and afterwards submitted to the same conditions.
For instance, a number of equally vigorous specimens had their
margins removed, and were then suspended in a glass cage

156 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

in this connection it is interesting to observe that,
although the endurance of the smaller segments

attached to a buoy in the sea. Four days afterwards some of the
specimens were putrid, while others were as fresh as they were
when first operated on. Again, as an instance of the experiments
in segmentation of Sarsia, I may quote an experiment in which a
scoi'e of specimens were divided in all sorts of ways, such as
leaving the manubrium attached to one half, or three marginal
bodies in one poi'tion and the remaining marginal body in the
other portion, etc. Yet, although it was very exceptional to find
the two portions presenting an equal degree of endurance, no
uniform results pointing to the cause of the variations could be
obtained. In most cases, however, the energy, as distinguished
from the endurance of the larger segments, was conspicuously
greater than that of the smaller. (But it is curious that in many
cases the effects of shock appeared to be more marked in the
larger than in the smaller segments — the latter, for some time
after the operation, conti-acting much more frequently than the
former.) To show both these effects, one experiment may be
quoted. A specimen of Sarsia was divided into two parts, of
which one was a quadrant.

Immediately after the operation the results were as follows : —

Portion i.

Portio:i f.

Number of pul-
sations.

Minutes of rest.

Number of jml-
.'■ations.

.Minutes of rest.

20
4

15
6

0
4
5
3

0

10
46
23
49
900
117

5

2

\

45

12

1
1

1

1

1145

13

To show the difference between the cnduranre of two halves of
a bisected specimen of Sarsia, I may quote one experiment which

NATURAL RHYTHM.

157

was less than that of the larger as regards the de-
privation of nutriment, it was greater than that of

^^.ls performed on tho same specimen as the one mentioned in
the text to show the general I'elationship between the duration of
the pauses and that of swimming bouts. (See last foot-note.)

Immediately after bisection.

iA.

IB.

Number of pul-
satio'is.

Seconds of rest.

Number of pul-
tatioas.

Seconds of rest.

56

10

82

180

150

150

51

20

68

3:^5

14

60

130

30

13

50

46

45

46

45

2

10

38

65

99

GG

18

45

103

3G0

23

GO

12

4

35

130

105

70

Pauses now become longer, and

swimming be

)uts sliorttr.

Twenty-four hours after the operation.

|A.

iB.

Number of pul-
sations.

Seconds of rest.

^"tt^nL^"^- • seconds of rest.

2
12

4
25

303
3G2
GfiG
300

50
81

37

2400

20

25

101

GO

But althnngh in the case of Sarsia the lesser endurance of the
smaller segment than of the larger cannot be regarded as a
general rule, it may be so regarded, as already stated, in the cas9

158 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

tlie larger segments as regards the deprivation of
oxygen. This is shown by the greater regularity

of Anrelia. The following experiment exemplifies this particular
rule even more prettily than does the one quoted in the text,
from the fact that the segments survived the operation for a
greater number of days.

An Aurclia having a regular and well-sustained rhythm of
twenty per minute was divided as already described in the text.
In five-minute intervals on successive days the average rates of
the four segments were as follows : —

Four hours after the operation.

Seg. h

Seg I

Seg. |.

Seg. 1 A.

100

100

S5

90

Next day.

88

90

04

5S

Next day.

86

82

G2

57

Nfxt day.

59

45

24

20

Next day.

50

49

20

10

Next (by.

43

33

18

4

Next day.

30

~ 32

19

Demi.

NATURAL HHYTHM.

159

of the rhythm manifested by the smaller than by
the larger segments in tlie stale water, and the
fact is presumably to be accounted for by the con-
sideration that the ganglia in tlie smaller segments
were more potent than those in the larger.

With rc-ard, therefore, to the original point
imder consideration, I conclude that, although the
size of the segments is doubtless one factor in
determining the relative frequency of contraction,
there are at least two other factors quite as impor-
tant, viz. the relative potency of the lithocysts, and
the length of time that elapses between performing
the operation and observing the rhythm. Hence it
is that in my experience I have found but very few
examples of Dr. Elmer's rule.

Effects of Other Forms of Mutilation on the Rhythn.

The next point I have to dwell upon is one of
some interest. If the manubrium of Aurelia, or of
any other covered-eyed Medusa, be suddenly cut off
at its base, the swimming motions of the umbrella

Next day.

Seg. h

Sog. \.

Seg. i.

S?g. I A.

S3

7

Dead.

0

Next day.

28

Dead.

1 »

0

Next day, the temperature unfortunately rose sufficiently to
cause the death of the single surviving segment, which otherwise
would probably have lived for one or two days longer.

160 JELL^-FISH, STAR-FISH, AND SEA-URCHINS.

immediately become accelerated. This acceleration,
however, only lasts for a few minutes, when it
gradually begins to decline, the rate of the rhythm
becoming slower and slower, until finally it comes
to rest at a rate considerably less than was pre-
viously manifested by the unmutilated animal. If
a circular piece be now cut out from the centre of
the umbrella, the rhythm of the latter again be-
comes temporarily quickened; but, as before, gradual
slowing next supervenes. This slowing, however,
proceeds further than in the last case, so that the
rate at which the rhythm next becomes stationary
is even less than before. If, now, another circular
ring be cut from the central part of the umbrella —
i.e. if the previously open ring into which this
organ had been reduced by the former operation be
somewhat narrowed from within — the same effects
on the rhythm are again observable; and so on
with every repetition of the operation, the rate of
the rhythm always being quickened in the first
instance, but then gradually slowing down to a
point somewhat below the rate it manifested before
the previous operation. It will here suffice to quote
one experiment among many I have made in this
connection : —

An Aurelia manifested a regular and snstained rhytbm of ... 26
Immediately after removal of manubrium, rhythm rose to ... 36
Rate then gradually fell for a quarter of an hoar, and became

stationaiy at . . . .. ... ... ... .. ... 20

Circular incision just inclndiug ovaries caused rhj'thm to

rise to ... ... ... ... ... ... ... 26

After gradual fall during quarter of an hour, rhythm became

stationary at ... ... .,, , ... 17

NATURAL RHYTHM. 161

Another circular incision carried round midway between the

former one and the margin caused rhythm to rise to ... 21

Rate again gradually declined, and in a quarter of an honr was 12

Another circular incision was carried round as close to the
margin as was compatible with leaving the physiological
continuity of all the lithocysts intact. RliyLhm rose to 14i

Within a few miuutes it fell to ... ... ... ... ... 6

Excepting the cases where the effects of shock
are apparent, some such series of phenomena as
those just recorded are always sure to ensue when
a covered-eyed Medusa is mutilated in the way
described, and this kind of mutilation, besides pro-
ducing such marked effects on the rate of the
rhythm, also produces an effect in impairing the
regularity of the rhythm. In some specimens
the latter effect is more marked than it is in others.
The following series of observations will serve to
give a good idea of this effect : —

An Aurelia manifested a regular and sustained
rhythm of 36. Immediately after the removal of
the manubrium, the rate of rhythm in successive
minutes was as follows : 40, 39, 37, 35, 32, 30, 29,
26, 24, 18, 14 (40 seconds' pause), 16, 15, 14, 15, 16
(40 seconds' pause), 22, 20, 19, 15, 16, 17, 14, 13, 13,
15, 16, 16, 17, 18, 14, 12, 13, 11, 12, 9, 15, 16, 14, 12,
9, etc., the rhythm now continuing very irregular.
An hour after the operation, the following were the
number of contractions given in one uinute inter-
vals, the observations being taken at intervals of
ten minutes: 15, ^D, 12, 22, 14, etc.

In this experiment, therefore, as soon as the ac-
celeration and slowing-stages had been passed, viz.
about a quarter of an hour after the operation, a

162 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

great disturbance was observable in regularity of
the rhythm ; for before the removal of the manu-
brium, the Medusa had been swimming for hours
with perfect regularity.

Before concluding my description of these experi-
ments, it may perhaps be as well to mention one
other, which was designed to meet a possible
objection to the inferences which, as I shall imme-
diately argue, these experiments seem to sustain. It
occurred to me as a remote possibility that the
slowing and irregularity of the rhythm, which are
observable about a quarter of an hour after the
operations described, might be due to the depriva-
tion of adequate nourishment suffered by the ganglia,
in consequence of the escape of nutrient matter
from the cut ends of the nutrient tubes. Accord-
ino-lv, instead of cuttino^ ofi* the manubrium, I tried
the effect of momentarily immersing it in hot water,
and found that the subsequent disturbances of the
rhythm were precisely similar to those which result
from removal of the manubrium.

Now, to draw any inferences from such meagre
facts as the above would be hazardous, unless we
recop^nize that in so doinor our inferences are not
trustworthy. But, with this recognition, I think
there will be no harm in briefly stating the deduc-
tions to which the facts, such as they are, would
seem to point.

Physiologists are undecided as to the extent in
which many apparently automatic actions may not
really be actions of a reflex kind. Given any
ganglio-muscular tissue which is rhythmically con-

NATURAL KHYTHM. 163

tracfcing, how are we to know whether the action
of the ganglia is truly automatic, or sustained
from time to time by stimuli proceeding from other
parts of the organism ? In most cases experiments
cannot be conducted with reference to this question,
but in the case of the Medusae the^^ may be so, and
it was with the view of throwing: lic^ht on this
question that the experiments just described were
made. Now in these experiments the fact is
sufficiently obvious that mutilations of any part of
the organism modify the rhythm of the marginal
ganglia most profoundly. That this modification
does not proceed from shock, would seem to be
indicated by the facts that the first efiect of the
mutilation is to quicken the rhythm; that there is a
sort of general proportion to be observed between the
amount of tissue abstracted and the deo-ree of sloAvinor
of the rhythm produced; and that the slowing efiects
continue for so long a time. All these facts seem
to show that we have here something other than
mere shock to deal with.

A strong suspicion, therefore, arises that the cause
of the slowing of the rhythm which results from
removing the manubrium, or a part of the general
contractile tissue of the bell, consists in the destruc-
tion of some influence of an afi[erent character which
had previously emanated from the parts of the
organism which have been removed, and that
the normal rhythm before the operation was partly
due to a continuous reception, on the part of the
ganglia, of this aflferent or stimulating influence.
In support of this view are the facts that the first

164! JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

effect of such an operation as we are considering is
greatly to accelerate the rhythm, and that this
acceleration then gradually declines through a period
of about a quarter of an hour. These facts tend to
support this view, because, if it is correct, they are
what we might anticipate. If the manubrium, for
instance, while in situ is continually supplying a
gentle stimulus to the marginal ganglia, when it is
suddenly cut off, the nerve-tracts through which
this stimulating influence had previously been con-
veyed must be cut through : and as it is well known
how irritable nerve-fibres are at their points of
section, it is to be expected that the irritation caused
by cutting these nerve-tracts, and probably also by
the action of the sea-water on their cut extremities,
would cause them to stimulate the ganglia more
powerfully than they did before their mutilation.
And here I may state that on several occasions,
with vigorous specimens, I have observed a sudden
removal of the manubrium to be followed, not
merely with a quickening of the rhythm on the
part of the bell, but with a violent and long-sustained
spasm.

Aorain, as rei^ards the other fact before us, it is
obvious that as soon as the cut extremities of the
nerves begin to die down, and so gradually to lose
their irritability, the effect on the rhythm would be
just what we observe it to be, viz. a gradual slowing
till the rate falls considerably below that which was
exhibited by the unmutilated animal. And even
the irregularity which is at this stage so frequently
observable is, I think, what we should expect to

NATURAL RHYTHM. 105

find if this view as to the essentially reflex character
of the natural rhythm is the true one.

If this view is the true one, the question next
arises as to the nature of the process which goes on
in the excitable tissues, and which afterwards acts
as a stimulus on the ganglionic tissues. This
question, however, I am quite unable to answer.
Whether the process is one of oxygenation, of
chemical changes exerted by the sea-water, or a
process of any other kind, further experiments may
be able to show ; but meanwhile I have no sugges-
tion to offer.

Effects of lessening the Amount of Tissue adhering
to a Single Ganglion.

The above experiments led me to try the effects
of cutting out a single lithocyst of Aurelia, and,
after the rhythm of the detached segment had
become regular, progressively paring down the
contractile tissues around the ffanolion. I found that
this process had no very marked effect on the
rhythm, until the paring reached within an inch or
two of the ganglion: then, however, the effect
began to show itself, and wi^h every successive
paring it became more marked. This effect con-
sisted in slowing the rate of the rhythm, but more
especially in giving rise to prolonged pauses: indeed,
if only a very little contractile tissue was left
adhering to the ganglion, the pauses often became
immensely prolonged, so that one might almost
suppose the ganglion to liave entirely ceased dis-

12

1G6 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

charging. But if a stimulus of any kind were then
applied, the rhythmic discharges at once recom-
menced. These generally continued for some little
time at a slower rate than that which they had
manifested before they Avere affected by the paring
down of the contractile tissue.

Ejects of Temperature on the Rhythm.

The effects of temperature on the rhythm of
Medasi3e are very decided. For instance, a specimen
of Sarsia which in successive minutes gave the
following number of pulsations, 16, 26, 0, 0, 26,
gave sixty pulsations during the next minute, while
a spirit-lamp was held under the water in which
the Medusa was swimminof. If hot water be added
to that in which Sarsia are contained until the
whole is about milk- warm, their swimming motions
become frantic. If the same experiment be per-
formed after the margins of the Sarsiae have been
removed, the paralyzed bells remain quite passive,
while the severed margins exhibit the frantic
motions just alluded to.

In the case of Aurelia aurita, the characteristic
effects of temperature on rhythm may be better
studied than in that of Sarsia, from the fact that
the natural motions ai-e more rhythmical and
sustained in the former than in the latter genus.
I have, therefore, in this connection made more
observations on Aurelia than on Sarsia. The follow-
ing may be taken as a typical experiment.

A small and active specimen of Aurelia contracted

NATURAL RHYTHM.

167

with the greatest regularity 33 times per minute in
water kept at 34°; but on transference to water
kept at 49'", the contractions always became irregular,
in respect (a) of not having a perfectly constant
rhythm, and (h) of exhibiting frequent pauses, which
was never the case in colder water. The rate of
rhythm in the warmer water varied from 37 to 49 ;
and as in these observations no allowance was
made for the occurrence of the pauses, the actual
rate of rhythm during the swimming motions was
about 60 per minute. The following are some
sample observations in the case of this specimen : —

Temperature of water (Falir.)

Number of pulsations.

Seconds of rest.

40°

41

5

»»

49

*

^rransferred to 31°

33

0

» "

c.

33

0

n »»

33

0

T) "

33

0

Transferred to 10°

45

4

M ')

39

10

»» »»

37

15

Transferred to 3t°

20

0

n »»

.. ...

30

0

W »5

,

33

0

>i »

38

0

n «

33

0

» «

33

0

This rate continued quite regularly for a quarter
of an hour, when the observation terminated.

It might naturally be supposed that when the
alterations of temperature between 34° and 49°
produce such marked effects on the rhythm, still

1C8 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

greater alterations would be attended with still
greater effects. Such, however, is not the case.
Water at 70° or 80°, for instance, has the effect of
permanently diminisJihig the rate of the rhythm,
after having temporarily raised it for a few seconds.
The following experiment will serve to convey a
just estimation of these facts.

An Aurelia whose rhythm in water at 40° was
very regular at eighteen per minute, was suddenly
transferred to water at 80°. In the immediately
succeeding minutes the rhythm was 22, 20, 14. The
latter rate continued for nearly half an hour, when
the observation terminated.

The effect of very warm water, therefore, is to slow
the rhythm, as well, I may add, as to enfeeble the
vio'our of the contractions. The case of Medusie
thus differs, in the former respect, from that of the
heart; and I think the reason of the difference is
to be found in the following considerations. Even
slight elevations of temperature are quickly fatal
to the Med usee, so it becomes presumable that con-
siderable elevations act very destructively on the
neuro-muscular tissues of those animals. This de-
structive effect of high temperatures may, therefore,
very probably counteract tlie stimulating effect which
such temperatures would otherwise exert on the
natural rhythm, and hence a point would somewhere
be reached at which the destructive effect would so
far overcome the stimulating effect as to slow the
rhythm. That this is probably the true, as it cer-
tainly is the only explanation to be rendered, will,
I think, be conceded when I further state that if

NATURAL RHYTHM. 169

an Aurclia be loft for some little time in water at
80°, and then again transferred to water at 30° or
40°, its original rate of rhythm at the latter tem-
perature does not again return, bat the rhythm
remains permanently slowed. And, in favour of
the explanation just offered, it may be further
pointed out that the first effect of sudden immer-
sion in heated water is to quicken the rhythm, it
not being for a few seconds, or for even a minute
or two after the immersion, that the rhythm be-
comes slowed. Lastly, the slowing takes place
gradually ; and this is what we should expect if,
as is probable, the destructive eftect takes some^vhat
more time to become fully developed than does the
stimulating effect.

Before leaving the subject of temperature in
relation to rhythm, I must say a few words on the
effects of cold. The following may be regarded as
typical experiments.

An Aurelia presenting a regular rhythm of
twenty per minute in water at 45° was placed in
water at 19°. Soon after the transference the
rhythm began to slow, and the strength of the
contractions to diminish. Both these phenomena
rapidly became more and more pronounced, till the
rhythm fell to ten per minute (still quite regular),
and the contractions ceased to penetrate the muscular
tissue further than an inch or so from the marginal
ganglia. Shortly after this stage pauses became
frequent, but mechanical or other irritation always
originated a fresh swimming bout. Next, only one
very feeble contraction was given at long and

170 jELLY-nsn, star-fish, and sea-urchins.

irregular intervals, a contraction so feeble that it
was restricted to the immediate vicinity of the
lithocyst in which it originated. Soon after this
stage irritability towards all kinds of stimuli entirely
ceased, including even strong spirit dropped on the
under surface of the animal when taken momentarily
out of the water. All these stages thus described
were passed through rapidly, the whole series occu-
pying rather less than five minutes. On now leav-
ing the specimen for ten minutes and then restoring
it to its original water at 45°, all the above-men-
tioned stages were passed through in reverse order.
The first faint marginal contraction was confined to
the immediate vicinity of the prepotent lithocyst,
and all subsequent contractions continued to be so
for the next three minutes. Rhythm very slow.
Contractions now began to penetrate round the
margin, and in eight minutes from the restoration
had gone all the way round, the rate of their
rhythm meanwhile increasing. In two minutes
more all the umbrella was contracting at the rate
of fifteen per minute.

In another specimen, subjected to the same con-
ditions, the rate of recovery was even more rapid,
occupying only two minutes altogether ; but in
every case the process of recovery is a gradual one,
and differs only in the time it occupies in passing
through the various stages.

Effects of Freezing Meduscs.

In conclusion, I will describe some rather interest-
ing experiments that consisted in freezing some

NATUKAL RHYTHM. 171

specimens of Aurelia into a solid block of ice. Of
course, as sea-water had to be employed, the cold
required was very considerable ; but I succeeded in
turning out the Medusae encased on all sides in a
continuous block of sea- water. By now immersing
this block in w^arm water, I was able to release the
contained specimens, which then presented a very
extraordinary appearance. The thick and massive
gelatinous bell of a Medusa is, as every one knows,
chiefly composed of sea-water, which everywhere
enters very intimately into the structure of the
tissue. Now, all this sea-water was, of course,
frozen in situ, so that the animals were every-
where and in all directions pierced through by an
innumerable multitude of ice-crystals, which formed
a very beautiful meshwork, pervading the whole
substance of their transparent tissues.

These experiments were made in order to ascertain
whether the Medusae, after having been thus com-
pletely frozen, would survive on being again thawed
out, and, if so, whether the freezing process would
exert any permanent influence on the rate of their
rhythm. Now in all the cases the Medusae, after
having been thawed out, presented a ragged ap-
pearance, which was due to the disintegrating
eflfect exerted by the ice-crystals while forming in
the tis^es ; yet notwithstanding this mechanical
injury superimposed on the physiological effects of
such extreme cold, all the Medusre recovered on
being restored to sea-water of the normal tem-
perature. The time occupied by the process of
recover}^ varied in different individuals from a few

172 JELLY-FISH, STAR- FISH, AND SEA-URCHINS.

minutes to half an hour or more, and it was observ-
able that those specimens which recovered soonest
had the rate of their rhythm least affected by the
freezino-. In no case, however, that I observed did
tlie rate of the rhythm after the freezing return
fully to that which had been manifested before the
freezing.

Effects of Certain Gases on the Rhythn.

Oxygen. — I will now conclude my remarks on
rhythm by very briefly describing the effects of
certain gases. Oxygen forced under pressure into
sea- water containing Sarsire has the effect of greatly
accelerating the rate of their rhythm. The follow-
ing observation on a single specimen will serve to
render this apparent.

Number of pulsations given by Sarsia in succes-
sive five-minute intervals.

In ordinary sea-water . . . 472, 527, 470

In oxygenated sea-water . . . 800

]u ordinary sea- water . . . 268, 350, 430

It will be seen from this observation that the
acceleration of the rhythm due to the oxygenation
was most marked ; indeed, the pulsations followed
one another so rapidly that it was no easy matter
to count them. It must also be stated that while
the animal was under the influence of oxygen, the
duration of the natural pauses between the swim-
ming bouts was greatly curtailed, the swimming
motions, in fact, being almost quite continuous
throuo-hout the five minutes tliat the Medusa was

NATURAL RHYTHM. 173

exposed to such influence. Lastly, it will be ob-
served from the above table that the unnatural
amount of activity displayed by the organism while
in the oxygenated water entailed on it a consider-
able degree of exhaustion, as shown by the fact
that even a quarter of an hour after its restoration
to normal water its original degree of energy had
not quite returned.

Carbonic acid. — As might be expected, this gas
has the opposite effects to those of oxygen. It is
therefore needless to say more about this agent,
except that if administered in large doses it destroys
both spontaneity and irritability. Nevertheless, if
its action is not allowed to last too long, the Medusae
will fully recover on being again restored to normal
sea-water.

Nitrous oxide. — This gas at first accelerates the
motions of Sarsia, but eventually retards them.
I omitted, however, to push the experiment to the
stage of complete anaesthesia, which would doubt-
less have supervened had the pressure of the gas
been sufficiently great.

Deficient aeration. — It may now be stated that
the Medusae are exceedingly sensitive to such slight
carbonization of the water in which they are con-
tained as results from their being confined in a
limited body of it for a few hours. The rhythm
becomes slowed and the contractions feeble, while
the pauses between the swimming bouts become
more frequent and prolonged. If the water is not
changed, all these sym[)toms become more marked,
and, in addition, the rhythm becomes very irregular.

174 JELLY-FJSH, STAll-FlSlI, AND SEA-URCHINS.

Eventually the swimming motions entirely cease ;
but almost immediately after the animals are
restored to normal sea-water, they recover them-
selves completely, the rate and regularity of their
rhythm being then quite natural. The suddenness
with which this return to the normal state of
things is effected cannot but strike the observer as
very remarkable, and I may menti(m that it takes
place with equal suddenness at whatever stage in
the above-described process of asphyxiation the
transference to normal sea- water is accomplished.

CHAPTER VIII.

ARTIFICIAL RHYTHM.

If the umbrella of Aurelia aurita has been para-
lyzed by the removal of its lithocysts, and if it is
then subjected to faradaic stimulation of minimal
intensity, the response which it gives is not tetanic,
but rhythmic. The rate of this artificial rhythm
varies in different specimens, but the limits of
variation are always within those which are ob-
served by the natural rhythm of diff*erent specimens.
The artificial rhythm is not in every case strictly
regular; but by carefully adjusting the strength of
the current, and by shifting the electrodes from one
part of the tissue to another until the most appro-
priate part is ascertained, the artificial rhythm
admits in most cases of being rendered tolerably
regular, and in many cases as strictly regular as is
the natural rhythm of the animal. To show this,
I append a tracing of the artificial rhythm (Fig.
25), which may be taken as a fair sample of the
most perfect regularity that can be obtained by
minimal faradaic stimulation.*

* This and all the subscqujut tracings I obtained by the
method already described.

ARTIFICIAL RHYTHM. 177

This artificial rhythm may be obtained with a
portion of in-itable tissue of any size, and whether
a large or small piece of the tissue employed be
included between the electrodes.

As the fact of this wonderfully rhythmic response
to faradaic irritation was quite unexpected by me,
and as it seemed to be a fact of great significance,
I was led to investigate it in as many of its bearings
as time permitted. First, I tried the etfect on the
rhythm of progressively intensifying the strength
of the faradaic current. I found that with each
increment of the current the rate of the rhythm
was increased, and this up to the point at which
the rhythm began to pass into tetanus due to sum-
mation of the successive contractions. But between
the slowest rhythm obtainable by minimal stimula-
tion and the most rapid rhythm obtainable before
the appearance of tetanus, there were numerous
degrees of rate to be observed. I here append
another tracing, to show the effect on the rate of
the rhythm of alterations in the strength of the
current (Fig. 20).

It will also be observed from this tracing that, in
consequence of the current having been strengthened
slightly beyond the limit within which strictly
rhythmic response was attainable, the curves in the
middle part of the tracing, where the current was
strengthened, are slightly irregular. This irregu-
larity is, of course, due to the first appearance of
tumultuous tetanus. If the faradaic stimulation
had in this case been progressively made still
stronger, the irre;rularity would have become still

178 JELLr-FlSII, STAR-FISn, AND SEA-URCHINS.

more pronounced up to a certain point, when it
would gradually have begun to pass into more
persistent tetanus. But as in this case, instead of
streno^thenino^ the current still further, I as^ain
weakened it to its original intensity, the rhythm
immediately returned to its original rate and regu-
larity.

Such being the facts, the question arises as to
their interpretation. At first I was naturally in-
clined to suppose that the artificial rhythm was
due to a periodic variation in the strength of the
stimulus, caused by some slight breach of contact
between the terminals and the tissue on each con-
traction of the latter. This supposition, of course,
would divest the phenomena in question of all
physiological meaning, and I therefore took pains
in the first instance to exclude it. This I did in
two ways : first, by observing that in many cases
(and especially in Cyanyea capillata) the rate of the
rhythm is so slow that the contractions do not
follow one another till a considerable interval of
total relaxation has intervened; and second, by
placing the terminals close together, so as to include
only a small piece of tissue between, and then
firmly pinning the tissue all round the electrodes to
a piece of wood placed beneath the Medusa. In
this way the small portion of tissue which served
as the seat of stimulation was itself prevented from
moving, and therefore the rhythmic motions which
the rest of the Medusa presented cannot have been
due to any variations in the quality of the contact
between the electrodes and this stationary scat of
stimulation.

A?.TIFICIAL RHYTHM. 179

Any such merely mechanical source of fallacj"
being thus, I think, excluded, we are compelled to
regard the facts of artificial rhythm as of a purely
physiological kind. The question, therefore, as to
the explanation of these facts becomes one of the
liighest interest, and the hypothesis which I have
framed to answer it is as follows. Every time the
tissue contracts it must as a consequence suffer a
certain amount of exhaustion, and therefore must
become slightly less sensitive to stimulation than
it was before. After a time, however, the ex-
haustion will pass away, and the original degree
of sensitiveness will thereupon return. Noav, the
intensity of faradaic stimulation which is alone
capable of producing rhythmic response, is either
minimal or but slightly more than minimal in
relation to the sensitiveness of the tissue when
fresh ; consequently, when this sensitiveness is
somewhat lowered by temporary exhaustion, the
intensity of the stimulation becomes somewhat less
than minimal in relation to this lower degree of
sensitiveness. The tissue, therefore, fails to perceive
the presence of the stimulus, and consequently fails
to respond. But so soon as the exhaustion is com-
pletely recovered from, so soon will the tissue again
perceive the presence of the stimulus ; it will there-
ibre again respond, again become temporarily ex-
hausted, again fail to perceive the presence of the
stimulus, and again become temporarily quiescent.
Now it is obviou.i tluit if this process occurs once,
it may occur an iudoiinite number of times; and
as the conditions of nutrition, as well as those of

180 JELLY-FISH, STAR-FISH, AND SEA-UllCHINS.

stimulation, remain constant, it is manifest that the
responses may thus become periodic.

In order to test the truth of this hypothesis,
I made the following experiments. Having first
noted the rate of the rhj^thm under faradaic stimu-
lation of minimal intensity, without shifting the
electrodes or altering the intensity of the current, I
discarded the faradaic stimulation, and substituted
for it single induction shocks thrown in with a key.
I found, as I had hoped, that the maximiimii num-
ber of these single shocks which I could thus throw
in in a given time so as to procure a response to
every shock, corresponded with the number of con-
tractions which the tissue had previously given
during a similar interval of time when under the
influence of the faradaic current of similar intensity.
To make this quite clear, I shall describe the whole
course of one such experiment. The degaiiglionated
tissue under the influence of minimal faradaic stimu-
lation manifested a perfectly regular rhythm of
thirty contractions per minute, or one contraction
in every two seconds. While the position of the
platinum electrodes and the intensity of the curi-ent
lemained unchancfed, single induction shocks were
now administered with a key at any intervals which
might be desired. It was found that if these single
induction stimuli were administered at regular
intervals of two seconds or more, the tissue re-
sponded to every stimulus; while if the stimuli
were thrown in more rapidly than this, the tissue
did not respond to every stimulus, but only to those
that were separated from one another by an interval

ARTIFICIAL RHYTHM. 181

of at least two seconds' duration. Thus, for in-
stance, if the shocks were thrown in at the rate of
one a second, the tissue only, but always, responded
to every alternate shock. And similarly, as just
stated, if any number of shocks were thrown in,
the tissue only responded once in every two seconds.
Now, as this rate of response precisely coincided
with the rate of rhythm previously shown by the
same tissue under the influence of faradaic stimula-
tion of the same intensity, the experiment tended to
verify the hypothesis which it was designed to test.
I may give one other experiment having the
same object and tendency. Employing single
induction shocks of slightly more than minimal
intensity, and throwing them in at twice the rate
that was required to produce a strong response to
every shock, I found that midway between every
two strong responses there was a weak response.
In other words, a stimulus of uniform intensity gives
rise alternately to a strong and to a weak contrac-
tion, as shown in the appended tracing (Fig. 27).
It will be observed that in this tracing^ each lar2:e
curve represents the whole time occupied by the
strong contraction, the latter beginning at the
, highest point of the curve on the left-hand side in
each case. The eiFect of the weak contraction is
that of momentarily interrupting the even sweep
of diastole after the strong contraction, and there-
fore the result on the tracing is a slight depression
in the otherwise even curve of ascent. Lest any
doubt should arise from the smallness of the curves
representing the weak contractions that the former
13

ARTIFICIAL RHYTHM. 183

are in some way accidental, I may draw attention
to the fact that the period of latent stimulation is
the same in the case of all the curves. To render
this apparent, I have placed crosses below the
smaller curves, which show in each case the exact
point where the depressing effect of these smaller
curves on the ascending sweeps of the larger curves
first become apparent — i.e. the point at which the
feeble contraction begins. Now, what I wish to be
gathered from the whole tracing is this. If the
strenofth of the induction shocks had been much
greater than it was, all the contractions would have
become strong contractions, and tetanus would have
been the result. But, as the strength of the in-
duction shocks was only slightly more than minimal,
the exhaustion consequent on every strong con-
traction so far diminished the irritability of the
tissue that when, during the process of relaxation,
another shock of the same intensity was thrown in,
the stimulus was only strong enough, in relation to
the diminished irritability of the partly recovered
tissue, to cause a feeble contraction. And these
facts tend still further to substantiate the hypothesis
whereby I have sought to explain the phenomena
of artificial rhythm.

Now, I think that the strictly rhythmic action
of the paralyzed swimming-bell of Aurelia in
answer to constant stimulation is a fact of the
highest significance ; for here we have a tissue
wholly, or almost wholly, deprived of its centres
of spontaneity, yet pulsating as rhythmically in
answer to artificial stimulation as it previously did

184 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

in answer to ganolionic stimulation.* Does not

O CD

this tend to show that for the production of the
natural rhythm the presence of the ganglionic
element is non-essential ; that if we merely suppose
the function of this element to be that of supplying
a constant stimulus of a low intensity, without in
addition supposing the presence of any special
resistance-mechanism to regulate the discharges,
the periodic sequence of systole and diastole would
assuredly result ; and, therefore, that the rhythmical
character of the natural swimming motions is
dependent, not on the peculiar relations of the
ganglionic, but on the primary qualities of the
contractile tissue ? Or, if we do not go so far as
this (and, as I may parentis etically observe, I am
not myself inclined to go so far), must we not at
least conclude that the natural rhythm of these
tissues is not exchisively due to any mechanism
whereby the discharges of the ganglia are inter-
rupted at regular intervals; but that whether these
discharges are supposed to be interrupted or
continuous, the natural rhythm is probably in a
large measure due to the same cause as the
artificial rliythm, viz. in accordance with our
previous hypothesis, to the alternate exhaustion
and recovery of the excitable tissues ? This much,
at least, must be allowed even by the most cautious

* It will not be forgotten that there are a mnltitnde of
ganglion-cells distributed throughout the contractile tissues of the
Medusae ; but forasmuch as these are comparatively rarely-
instrumental in originating stimulation, I think it is probable
that artificial stimulation acts directly on the contractile tissues,
and not through the medium of these scattered cells.

ARTIFICIAL RHYTHM. 185

of critics, viz. that if, as current views respecting
the theory of rhythm would suppose, it is ex-
clusively the ganglionic element which in the
unmutilated Aurelia causes the rhythm of the
swimming motions by intermittent stimulation,
surely it becomes a most unexpected and unaccount-
able fact, that after the removal of this element the
contractile tissues should still persist in their
display of rhythm under the influence of constant
stimulation. At any rate no one, I think, will
dispute that the facts which I have adduced justify
us in reconsidering the whole theory of ihythm as
due to ganglia.

As I have already said, I am not inclined to
deny that there is probably some truth in the
current theory of rhythm as due to ganglia; 1
merely wish to point out distinctly that this theory
is inadequate, and that in order to cover all the
facts it will require to be supplemented by the
theory which I now propose. The current theory
of rhythm as due to ganglia attributes the whole
of the effect to the ganglionic element, and thus
fails to meet the fact of a rhythm which is artifi-
cially produced after the ganglionic element has
been removed. It also fails to meet a number of
other facts of the first importance ; for it is be-
yond all doubt that rhythmic action of the strictest
kind occurs in an innumerable multitude of cases
where it is quite impossible to suppose anything
resembling ganglia to be present. Not to mention
such cases as the Snail's heart, where the most
careful scrutiny has failed to detect the least ves-

186 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

tige of ganglia, but to descend at once to the
lowest forms of animal and vegetable life, rhythmic
action may here be said to be the rule rather than
the exception. The beautifully regular motions
observable in some Alg?e, Diatomacese, and Ocilla-
torise, in countless numbers of Infusoria, Anthero-
zoids, and Spermatozoa, in ciliary action, and even
in the petioles of Hedysarum gyrano, are all in-
stances (to which many others might be added) of
rhythmical action where the presence of ganglia
is out of the question. Again, in a general way,
is it not just as we recede from these primitive
forms of contractile tissue that we find rhythmic
action to become less usual ? And, if this is so,
may it not be that those contractile tissues which
in the higher animals manifest rhythmic action are
the contractile tissues which have longest retained
their primitive endowment of rhythmicality ? To
my mind it seems hard to decide in what respect
the beating of a Snail's heart differs from that of
the pulsatile vesicles of the Infusoria; and I do
not think it would be much easier to decide in what
essential respect it differs from the beating of the
Mammalian heart. The mere fact that the presence
of ganglia can be proved in the one case and not
in the other, seems to me scarcely to justify the
conclusion that the rhythm is in the one case
wholly dependent, and in the other as wholly in-
dependent, of the ganglia. At any rate, this fact,
if it is a fact, is not of so self-evident a character
as to recommend to us the current theory of gang-
lionic action on d priori grounds.

ARTIFICIAL IllIYTHM. 187

Coming, then, to experimental tests, we have
already seen that in the deganglionated swimming
organ of Anrclia aiirita, rhythmic response is yielded
to constant faradaic stimulation of low intensity.
The next question, therefore, which presents itself
in relation to our subject is as to whether other
modes of constant stimulation elicit a similar re-
sponse. Now, in a general way, I may say that
such is the case, although I have chosen faradaic
stimulation for special mention, because, in the first
place, its effect in producing rhythmic action is the
most certain and precise; and, in the next place,
the effects of administering instantaneous shocks
at given intervals admit of being compared with
the effects of constant faradaic stimulation better
than with any other kind of constant stimulation.
Nevertheless, as just stated, other modes of con-
stant stimulation certainly have a more or less
marked effect in producing rhythmic response. The
constant current, during the whole time of its
passage, frequently has this effect in the case of
the paralyzed nectocalyx of Sarsia ; and dilute spirit,
or other irritant, when dropped on the paralyzed
swimming organ of Aurelia aurita, often gives rise
to a whole series of rhythmical pulsations, the sys-
toles and diastoles following one another at about
the same rate as is observable in the normal swim-
ming motions of the unmutilated animal.

From this it will be seen that, both in the case
of mechanical and of chemical stimulation, the same
tendency to the production of rhythmic response
on the part of the paralyzed tissues of Aurelia may

188 JELLY-FISir, STAR-FISH, AND SEA-URCHINS.

be observed as in the case of electrical stimulation.
The principal differences consist in the rhythm
being much less sustained in the former than in
the latter case. But, by experimenting on other
species of Medusae, I have been able to obtain,
in response to mechanical and chemical stimula-
tion, artificial rhythm of a much more sustained
character than that which, under such modes of
stimulation, occurs in Aurelia. I have no explana-
tion to offer why it is that some species, or some
tissues, present so much more readiness to manifest
sustained rhythm under certain modes of stimula-
tion, and less readiness to manifest it under other
modes, than do other species or tissues. Probably
these differences depend on some peculiarities in
the irritability of the tissues which it is hopeless
to ascertain; but, in any case, the facts remain,
that while Aurelia, Cyanaea, and the covered-eyed
Medusae generally are the best species for obtaining
artificial rhythm under the influence of faradaic
stimulation, some of the naked-eyed Medusae are
the best species for obtaining it under the influence
of the constant current, and also under that of
mechanical and chemical stimulation. I have
already spoken of this effect of the constant cur-
rent in the case of Sarsia; I shall now proceed
to describe the effects of mechanical and chemical
stimulation on the same species.

It is but rarely that artificial rhythm can be pro-
duced in the paralyzed nectocalyx of Sarsia by
means of mechanical stimulation, but in the case
of the manubrium, a very decided, peculiar, and

ARTIFICIAL RHYTHM. 189

persistent rh^^tlim admits of being produced by
this means. lu this particular species, the manu-
brium never exhibits any spontaneous motion after
the ganglia of the nectocalyx have been removed.
But if it be nijiped with the forceps, or otherwise
irritated, it contracts strongly and suddenly ; it
then very slowly and gradually relaxes until it has
regained its original k-ngth. After a considerable
interval, and without the application of any addi-
tional stimulus, it gives another single, sudden,
though slight contraction, to be again followed by
gradual relaxation and a prolonged interval of
repose, which is followed in turn by another con-
traction, and so on. These sudden and well-marked
contractions occur at intervals of many seconds,
and show a decided tendency to rhythmic periodi-
city, though the rhythm is not always perfectly
exact. This intensely slow rhythm, as the result
of injury, may continue for a long time, particu-
larly if the injury has been of a severe character.
There can be no doubt, therefore, that the mecha-
nical (or other) injury in this case acts as a source
of constant irritation ; so that here again we have
evidence of rhythmic action independent of ganglia,
and caused by the alternate exhaustion and re-
covery of contractile tissues.*

* We may pretty safely conclude that ganglia are altogether
absent in the manubrium of Sarsia, not only because Schultz
has failed to detect them in this organ microscopically, but also
because of the complete absence of spontaneity which it mani-
fests. I may here mention that this case of the manubrium of
Sarsia is precisely analogous to another which I have observed in
a widely different tissue, namely, the tongue of the frog. Here,

190 JELLY-FISH, STAR-FISH, AND SEA-UECHINS.

With regard to artificial rhythm caused by-
chemical stimuli, by far the most conspicuous
instance that I have observed is that of the para-
lyzed nectocalyx of Sarsia. This consists in a
highly peculiar motion of a flurried, shivering
character, which is manifested by this organ when
its marginal ganglia have been removed and it is
exposed to the influence of faintly acidulated water.
Now, when read in the light of the foregoing facts,
there can be no doubt that the present one falls
into its place very satisfactorily : it is an additional
and very valuable instance of the display of arti-
ficial rhythm under the influence of a constant
stimulus of low intensity ; for the shivering
motions of the mutilated nectocalyx under these
circumstances are most unmistakably of a rhythmic
nature. Viewed from a little distance, indeed, these
motions are not distinguishable from the natural
swimming motions of the unmutilated animal,
except that, not being of quite such a powerful
character, they are not so eftective for locomotion.
Viewed more closely, however, it may frequently be
seen that the whole bell does not contract simul-
taneously, but that, as it were, clouds of contraction
pass now over one part and now over another.
Still, whether the contractions are partial or uni-
versal, they are more or less rhythmical. As this
was the only case that had ever been observed of

too, the presence of ganglion-cells has never been observed micro-
scopically, though specially souglit for by Dr. Klein and others.
Yet, under the influence of mechanical and other modes of stimu-
lation, I find that I am able to make the excised organ pulsate as
rhythmically as a heart.

ARTIFICIAL RHYTHM. 191

rhythm as due to a constant chemical stimulus,
I studied it with much care, and shall now give
a full description of what appears to me an im-
portant body of physiological facts.

Ten to twenty drops of acetic acid having been
added to one thousand cubic centimetres of sea-
water, and the paralyzed bell of Sarsia having been
placed in the mixture, an interval of about half a
minute will elapse before any movement begins.
Sooner or later, however, the artificial rhythm is
6ure to be induced, and it will then continue for
a variable time — occasionally as long as an hour,
and generally for a considerable number of minutes.
After it ceases it may often be made to recommence,
either by adding a few more drops of acid to the
sea-water, or by supplying an additional stimulus
to the bell by nipping it with the forceps. Even-
tually, however, all movement ceases, owing to the
destruction of irritability by the action of the acid.
By this time the whole inner surface of the bell has
become strongly opalescent, owing to the destruc-
tive influence of the acid on the epithelial cells
which overspread the irritable tissues. The latter
fact is worth men'-ioning, because in no case does
the artificial rhythm set in until this opalescence
has begun to show itself ; and as this opalescence
is but an optical expression of the damage which
the epithelial coat is undergoing, the explanation of
the time which elapses after the first immersion
of the bell in the acidulated water and the com-
mencement of the artificial rhythm no doubt is,
that duri])g this time the acid has not obtained

192 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

sufficient access to the excitable tissues to serve as
an adequate stimulus.

During the soaking stage of the ex|)eriment — i.e.
before the artificial rhythm begins — the excitability
of the tissues may be observed progressively and
abnormally to increase ; for soon after the soaking
stage begins, in response to a single nip with the
forceps the bell may give two or three locomotor
contractions, instead of a single one, as is invariably
the case with a paralyzed bell of Sarsia in normal
water. Later on during the soaking stage, four or
five successive contractions may be yielded in
response to a single mechanical stimulus, and shortly
after this a whole bout of rhythmic contractions
may be started by the same means. Indeed, in
some cases the artificial rhythm in acidulated water
requires such a single additional stimulus for its
inauguration, the shivering movements failing to
begin spontaneously, but beginning immediately
upon the application of the additional stimulus.
Similarly, after the shivering movements have
ceased, a fresh bout may very often be started by
again giving the motionless nectocalyx a single
stimulation. The interpretation of these facts
would seem to be that the general irritability of
the excitable tissues is exalted by the universal and
constant stimulus supplied by the acid to an extent
that is just bordering on that which gives rise to
rhythmic movement, so that when the violent con-
traction is given in response to the mechanical
stimulus, the disturbance serves to start the rhythmic
movement.

ARTIFICIAL RHYTHM. 193

If a paral3^zed nectocalyx, while manifesting its
artificial rhythm in acidulated sea-water, be sud-
denly transferred to normal sea- water, the move-
ments do not cease immediately, but continue for
a considerable time. This fact can easily be ex-
plained by the very probable, and indeed almost
necessary, supposition that it takes some time after
the transference to the normal saa-water for the
acid to be washed out from contact with the ex-
citable tissues. Sooner or later, however, as we
should expect, in the normal sea-water the rhythmic
movements entirely cease, and the bell becomes
quiescent, with a normal irritability as regards
single stimuli. If it be now again transferred to
the acidulated water, after a short interval the
rhythmic movements will again commence, and so
on during several repetitions of this experiment,
until the irritability of the tissues has finally
become destroyed by the influence of the acid.

Other chemical irritants which I have tried pro-
duce substantially similar effects on the paralyzed
bell of Sarsia. I shall, therefore, only wait to
describe the influence of one of these irritants, the
action of which in some respects diflers from that
of acids, and which I have found to be one of the
most unfailing in its power to produce the rhythmic
movements in question. This irritant is glycerine,
and in order to produce its full effect it requires to
be added to the sea-water in about the proportion
of five per cent. The manifestation of artificial
rhythm in solutions of this kind is quite unfailing.
It begins after an exposure of from fifteen to thirty

194* JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

seconds, and continues for a variable number of
seconds. It generally begins with powerful con-
tractions, of a less shivering character than those
which are produced by acids, and therefore still
more closely resembling the normal swimming
motions of the unmutilated animal. Sometimes,
however, the first manifestation of the artificial
rhythm is in the form of a few gentle rhythmic
contractions, to be followed by a few seconds of
quiescence, and then by the commencement of the
sustained bout of strong contractions. In either
case, when the bout of strong contractions sets in,
the rate of the rhythm becomes progressively and
rapidly increased, until it runs up into incipient
tetanus. The rate of the rhythm still quickening,
the tetanus rapidly becomes more and more pro-
nounced, till at last the bell becomes quiescent in
tonic spasm.*

If the bell is still left in the glycerine solution
nothing further happens; the tissues die in this
condition of strong systole. But if the bell be
transferred to normal sea-water immediately after,
or, still better, slightly before the tonic spasm has
become complete, an interesting series of pheno-
mena is presented. The spasm persists for a long

* Sometimes, however, the order of events is slightly different,
the advent of the spasm being more sudden, and followed by a
mitigation of its severity, the bell then exhibiting what is more
usually the first phase of the series, namely, the occurrence of
the locomotor-like contractions. Occasionally, also, rhythmical
shivenng contractions may be seen superimposed on the general
tonic contraction, either in a part or over the whole of the con-
tractile tissues.

ARTIFICIAL RHYTHM. 195

time after the transference without undergoing any
change, the length of this time depending on the
stage in the severity and the spasm at which the
transference is made. After this time is passed,
the spasm becomes less pronounced than it was at
the moment of transference, and a reversion takes
place to the rhythmic contractions. The spasm
may next pass off entirely, leaving only the rhythmic
contractions behind. Eventually these too fade
away into quiescence, but it is remarkable that
they leave behind them a much more persistent
exaltation of irritability than is the case with acid.
For in the case of glycerine, the paralyzed bell
which has been exposed to the influence of the
irritant and afterwards become quiescent in normal
sea-water, Avill often continue for hours to respond
to single stimuli with a bout of rhj^thmic contrac-
tions. This effect of glycerine in producing an
extreme condition of exalted irritability is also
rendered apparent in another way ; for if, during
the soaking stage of the experiment — i.e. before the
first of the rhythmic contractions has occurred —
the bell be nipped with the forceps, the effect may
be that of so precipitating events that the whole of
the rhythmic stages are omitted, and the previously
quiescent bell enters at once into a state of rigid
tonic spasm. This effect is particularly liable to
occur after prolonged soaking in weak solutions of
glycerine.

As in the case of stimulation by acid, so in that
of stimulation by glycerine, the artificial rhythm
never begins in any strength of solution until the

196 JELLY-FISH, STAR-FISn, AND SEA-URCHINSw

epithelial surface has become opalescent to a con-
siderable degree.

In the case of stimulation by glycerine, the be-
haviour of the manubrium is more unequivocal
than it is in the case of stimulation by acid. I
have therefore reserved till now my description of
the behaviour of this organ under the influence of
constant chemical stimulation. This behaviour is
of a very marked though simple character. The
manubrium is always the first to respond to the
stimulation, its retraction preceding the first
movements of the bell by an interval ot several
seconds, so that by the time the bell begins its
rhythmic response the manubrium is usually re-
tracted to its utmost. The initial response of the
manubrium is also rhythmic, and the rhythm
which it manifests — especially if the glycerine
solution be not over-strong — is of the same slow
character which has already been described as
manifested by this organ when under the influence
of mechanical stimulation. The rhythm, however,
is decidedly quicker in the former than in the latter
case.

Lastly, with regard to the marginal ganglia, it is
to be observed that in the case of all the chemical
irritants I have tried, if unmutilated specimens of
Sarsia be immersed in a sea-water solution of the
irritant which is of a sufficient strength to evoke
artificial rhythm in paralyzed specimens, the spon-
taneity of the ganglia is destroyed in a few seconds
after the immersion of the animals, i.e. in a shorter
time than is required for the first appearance of

ARTIFICIAL RHYTHM. 197

artificial rhythm. Consequently, whether the
specimens experimented upon be entire or paralyzed
by removal of their margins, the phenomena of
artificial rhythm under the influence of chemical
stimulation are the same. But although the spon-
taneity of the ganglia disappears before the artificial
rhythm sets in, such is not the case with the reflex
activity of the ganglia ; for on nipping a tentacle of
the quiescent bell before the artificial rhythm has
set in, the bell will give a single normal response to
the stimulation.

Hence, in historical order, on dropping an unmuti-
lated specimen of Sarsia into a solution of glycerine
of the strength named, the usual succession of events
to be observed is as follows. First, increased
activity of the normal swimming motions, to be
quickly followed by a rapid and progressive decrease
of such activity, till in about fifteen seconds after
the immersion total quiescence supervenes. Four
or five seconds later the manubrium begins to re-
tract by rhythmical twitches, the rate of this
rhythm rapidly increasing until it ends in tonic
contraction. When the manubrium has just become
fully retracted — or very often a little earlier — the
bell suddenly begins its forcible and well-pro-
nounced rhythmic contractions, which rapidly in-
crease in their rate of rhythm until they coalesce
into a vigorous and persistent spasm. If the animal
be now restored to normal sea -water, spontaneity
will return in a feeble manner ; but there is always
afterwards a great tendency displayed by the bell
to exhibit shivering spasms instead of norma'

14

108 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

swimming movements in response to natural or
ganglionic stimulation. And, as already observed,
this peculiarity of the excitable tissues is also well
marked in the case of the artificial stimulation of
degangiionated specimens under otherwise similar
conditions.

One further experiment may here be mentioned.
Having split open the paralyzed bell of Sarsia along
the whole of one side from base to apex of the cone,
I suspended the now sheet-like mass of tissue by
one corner in the air, leaving the rest of the sheet
to hang vertically downwards. By means of a
rack-work support I now lowered the sheet of tissue,
till one portion of it dipped into a beaker filled
with a solution of glycerine of appropriate strength.
After allowing this portion to soak in the solution
of glycerine until it became slightly opalescent, I
dropped the entire mutilated bell, or sheet of tissue,
into another beaker containing sea-water. If the
exposure to the glycerine solution had been of
sufficient duration, I invariably found that in the
normal sea-water the rhythmic movements were
performed by the whole tissue-mass quite as
efficiently as was the case in my other experiments,
where the whole tissue-mass, and not merely a por-
tion, had been submitted to the influence of the
irritant. But on now suddenly snipping ofl[' the
opalescent portion of the tissue-mass, i.e. the por-
tion which had been previously alone submitted to
the influence of the irritant, all movement in the
remainder of the tissue-mass instantly ceased. This
experiment I performed repeatedly, sometimes ex-

ARTIFICIAL RHYTHM. 199

posing a large and sometimes a small portion of the
tissue to the influence of the irritant. As I in-
variably obtained the same result, there can be no
doubt that in the case of chemical stimulation the
artificial rhythm depends for its manifestation on
the presence of a constant stimulus, and is not
merely some kind of obscure fluttering motion
which, having been started by a stimulus, is after-
wards kept up independently of any stimulus.

Such being the case, I naturally expected that if
I were to supply a constant stimulus of a thermal
kind, I should also obtain the phenomena of arti-
ficial rhythm. In this, however, my expectations
have not been realized. With no species of Medusa
have I been able to obtain the slightest indication
of artificial rhythm by immersing the paralyzed
animals in heated water. I can only explain this
fact by supposing that the stimulus which is sup-
plied by the heated medium is of too uniform a
character over the whole extent of the excitable
tissues; it would seem that in order to produce
artificial rhythm there must be a differential in-
tensity of stimulation in difTerent parts of the
responding tissue, for no doubt even the excitatory
influence of acidulated water is not of nearly so
uniform an intensity over the whole of the tissue-
area as is tbat of heated w^ater.

In now quitting the subject of artificial rhythm
as it is manifested by the paralyzed bell of Sarsia,
it is desirable again to observe that sustained
artificial rhythm cannot be produced by means of
chemical irritation in the case of any one of the

200 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

species of covered-eyed Medusae that I have met
with. In order to evoke any response at all,
stronger solutions of the irritants require to be em-
ployed in the case of the covered than in that of the
naked-eyed Medusa3, and when the responses do occur
they are not of so suggestive a character as those
which I thought it worth while so fully to describe.
Nevertheless, even in the covered-eyed Medusae
well marked, though comparatively brief, displays
of artificial rhythm may often be observed as the
result of constant chemical stimulation. Thus, for
instance, in the case of Aurelia, if the paralyzed
umbrella be immersed in a solution of glycerine
(ten to twenty per cent.), a few rhytlimic pulsa-
tions of normal rate are usually given ; but shortly
after these pulsations occur, the tissue begins to go
into a tetanus, which progressively and rapidly
becomes more and more pronounced until it ends in
violent tonic spasm. So that the history of events
really resembles that of Sarsia under similar cir-
cumstances, except that the stage of artificial
rhythm which inaugurates the spasm is of a
character comparatively less pronounced.

Thus far, then, I have detailed all the facts which
I have been able to collect with reference to the
phenomena of artificial rhythm, as produced by
different kinds of constant stimulation. It will not
be foro'otten that the interest attaching^ to these
facts arises from the bearing which they have on
the theory of natural rhythm. My belief is that
hitherto the theory of rhythm as due to ganglia has
attributed far too nuich importance to the ganglionic

ARTIFICIAL RHYTHM. 201

as distinguished from the contractile tissues, and I
have founded this belief principally on the facts
which have now been stated, and which certainly
prove at least this much : that after the removal of
the centres of spontaneity, the contractile tissues
of the Medus?e display a marked and persistent
tendency to break into rhythmic action whenever
they are supplied w^ith a constant stimulus of feeble
intensity. Without waiting again to indicate how
this fact tends to suggest that the natural rhythm
of the unmutilated organisms is probably in large
part due to that alternate process of exhaustion
and restoration of excitability on the part of the
contractile tissues, whereby alone the phenomena
of artificial rhythm can be explained,* I shall go
on to describe some further experiments which were
designed to test the question whether the influences
which affect the character of the natural rhythm
likewise, and in the same manner, affect the
character of the artificial rhythm. I took the
trouble to perform these experiments, because I felt
that if they should result in answering this question
in the affirmative, they would tend still further to

* It is of importance to point out the fact that some of my
previously stated experiments appear conclusively to prove that
the natural stimulation which is supplied by the marginal ganglia
of the Medusae resembles all the modes of artificial stimulation
which are competent to produce artificial rhythm in one im-
portant particular; the intensity of the stimulation which the
marginal ganglia supply is shown by these experiments to be
about the same as that which is required to produce artificial
rhythm in the case of artificial stimulation. In proof of this
point, I may allude particularly to the observations which are
detailed on pp. 134-136.

202 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

substantiate the view I am endeavouring to uphold,
viz. that the natural rhythm may be a function
of the contractile as distinguished from the gang-
lionic tissue. Of the modifying causes in question,
the first that I tried was temperature.

Having already treated of the effects of tem-
perature on the natural rhythm, it will now be
sufiicient to say that we have seen these effects to
be similar to those which temperature exerts on
the rhythm of ganglionic tissues in general. Now,
I find that temperature exerts precisely the same
influence on the artificial rhythm of deganglionated
tissue as it does on the natural rhythm of the un-
mutilated animal. To economize space, I shall only
quote one of my observations in a table which ex-
plains itself. I also append tracings of another obser-
vation, to render the difference in the rate of the
artificial rhythm more apparent to the eye (Fig. 28).

^rature of water

Number of contractions

(Fabr.).

per minute.

25°

24

45°

40

75°

60

During the whole progress of such experiments
the faradaic stimulation was, of course, kept of
uniform intensity; so that the progressive ac-
celeration is undoubtedly due to the increase of
temperature alone. With each increment of tem-
perature the rate of the artificial rhythm increases
suddenly, just as it does in the case of the natural
rhythm. Moreover, there seems to be a sort of
rough correspondence between the amount of in-

0 J _

10 -

E^ (

t/3

8

204 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

fluence that any given degree of temperature exerts
on the rate of the natural and of the artificial
rhythm respectively. Further, it will be remembered
that in warm water the natural rhythm, besides
being quicker, is not so regular as it is in cold
water; thus also it is with the artificial rhythm.
Again, water below 20° or above 85° suspends the
natural rhythm, i.e. stops the contractions; and
the artificial rhythm is suspended at about the
same degrees. Lastly, just as there are considerable
individual variations in the extent to which the
natural rhythm is affected by temperature, so the
artificial rhythm is in some cases more influenced by
this cause than in others, though in all cases it
further resembles the natural rhythm in showing
some considerable degree of modification under
such influence.

On the whole, then, it would be impossible to
imagine two cases more completely parallel than
are these of the effects of temperature on natural
and on artificial rhythm respectively; and as it
must be considered in the last degree improbable
that all these coincidences are accidental, I conclude
that the effects of temperature on the natural
rhythm of Medusae (and so, in all probability, on
the natural rhythm of other ganglio-muscular
tissues) are for the most part exerted, not on the
ffanHionic, but on the contractile element.

In order to test the effects of gases on the
artificial rhytlim, I took a severed quadrant of
Aurelia, and floated it in sea-water, with its
muscular surface just above the level of the water.

ARTIFICIAL RHYTHM. 205

Over the tissue I lowered an inverted beaker filled
with the gas the effects of which I desired to
ascertain, and by progressively forcing the rim of
the beaker into the water I could submit the tissue
to various pressures of the atmosphere of the gas
I was using. By an appropriate arrangement the
electrodes passed into the interior of the beaker,
and could then be manipulated from the outside, so
as to be properly adjusted on the tissue. In this
way I was able to observe that different gases
exerted a marked influence on the rate of the
artificial rhythm.

The following table gives the ratios in the case
of one experiment : —

Rate of artificial rhythm,
in air.

36 per minute.

In oxygen.
50 per minute.

In carbonic acid.
25 per minute.

It may here be observed that to produce these
results, both carbonic acid and oxygen must be
considerably diluted with air, for otherwise they
have the effect of instantaneously inhibiting all
response, even to the strongest stimulation. When
this is the case, however, irritability returns very
soon after the tissue is again exposed to air or to
ordinary sea-water. But I desire it to be under-
stood that the results of my experiments on the
influence of oxygen, both on the natural and on the
artificial rhythm, have proved singularly equivocal ;
so that as far as this gas is concerned further
observations are required before the above results
can be accepted as certain.

I have still one other observation of a very

206 JELLY-FISH, STAR-FISII, AND SEA-UKCHINS.

interesting character to describe, which is closely
connected with the current views respecting gan-
glionic action, and may therefore be more con-
veniently considered here than in any other part of
this treatise. I have already stated that in no case
is the manubrium of a Medusa affected as to its
movements by removal of the periphery of the
swimming-bell ; but in the case of Sarsia a very
interestino- chancre occurs in the manubrium soon
after the nectocal^^x has been paralyzed by excision
of its margin. Unlike the manubriums of most of
the other Medusce, this organ, in the case of Sarsia,
is very highly retractile. In fresh and lively speci-
mens the appendage in question is carried in its
retracted state ; but when the animals become less
vigorous — from the warmth or impurity of the
water in which they are confined, or from any
other cause — their manubriums usually become
relaxed. The relaxation may show itself in various
degrees in different specimens subjected to the same
conditions, but in no case is the degree of relaxa-
tion so remarkable as that which may be caused
by removing the periphery of the nectocalyx. For
the purpose of showing this effect, it does not
signify in what condition as to vigour, etc., the
specimen chosen happens to be in ; for whether
the manubrium prior to the operation be contracted
or partially relaxed, within half an hour after the
operation it is sure to become lengthened to a
considerable extent.

In order to shovv^ the surprising degree to which
this relaxation mr.y proceed, I insert a sketch of a

ARTIFICIAL RHYTHM.

207

specimen both before and after the operation. The
(^ketches are of life size, and drawn to accurate
measurement (Figs. 29 and 30).*

Fig. 29.

30.

With regard to this remarkable effect on the
manubrium of removing the margin of the necto-
calyx, it is now to be observed that in it we
appear to have very unexceptionable evidence of
such a relation subsisting between the ganglia
of the nectocalyx and the muscular fibres of
the manubrium as elsewhere gives rise to what
is known as muscular tonus. This inter])retation

* I may here mention that the fact of the manubrium of Sarsia
undergoing this extreme elongation after the removal of the mar-
ginal ganglia, serves to render the artificial rhythm of the organ
under the influence of injury, as previously described, all the more
conspicuous.

208 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

of the facts cannot, I think, be disputed ; and it
fully explains why, in the unmutilated animal, the
degree of elongation on the part of the manubrium
usually exhibits an inverse proportion to the degree
of locomotor activity displayed by the bell. I may
here state that I have also observed indications of
muscular tonus in some of the other Medusae, but
for the sake of brevity I shall now restrict myself
to the consideration of this one case.

To my mind, then, it is an interesting fact that
orano^lionic tissue, where it can first be shown to
occur in the animal kingdom, has for one of its
functions the maintenance of muscular tonus ; but
it is not on this account that I now wish to draw
prominent attention to the fact before us. Physio-
logists are almost unanimous in regarding muscular
tonus as a kind of gentle tetanus due to a persistent
ganglionic stimulation, and against this opinion it
seems impossible to urge any valid objection. But,
in accordance with the accepted theory of gan-
glionic action, physiologists further suppose that the
only reason why some muscles are thrown into a
state of tonus by ganglionic stimulation, while other
muscles are thrown into a state of rhythmic action
by the same means, is because the resistance to the
passage of the stimulation from the ganglion to
the muscle is less in the former than in the latter
case. Here, be it remembered, we are in the
domain of pure speculation : there is no experi-
mental evidence to show that such a state ot
differential resistance as the theory requires actu-
ally obtains. Hence we are quite at liberty to

ARTIFICIAL RHYTHM. 209

suppose any other kind of difference to obtain,
either to the exclusion of this one or in company
with it. Such a supposition I now wish to suggest,
and it is this — that all rhythmical action being
regarded as due (at any rate in large part) to the
alternate exhaustion and restoration of excitability
on the part of contractile tissues, the reason why
continuous ganglionic stimulation produces incipient
tetanus in the case of some muscles and rhythmic
action in the case of others, is either wholly or
partly because the irritability of the muscles in
relation to the intensity of the stimulation is greater
in the former than in the latter case. If this sup-
position as to differential irritability be granted,
my experiments on paralyzed Aurelia prove that
tetanus would result in the one case and rhythmic
action in the other. For it will be remembered that
in these experiments, if the continuous faradaic
stimulation were of somewhat more than minimal
intensity, tetanus was the result; while if such
stimulation were but of minimal intensity, the
result was rhythmic action. Now, that in the
particular case of Sarsia the irritability of the toni-
cally contracting manubrium is higher than that
of the rhythmically contracting bell is a matter,
not of supposition, but of observable fact ; for not
only is the manubrium more irritable than the bell
in response to direct stimulation of its own sub-
stance, but it is generally more so even when the
stimuli are applied anywhere over the excitable
tissues of the bell. And from this it is evident
that the phenomena of muscular tonus, as they

210 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

occur in Sarsia, tend more in favour of the exhaus-
tion than of the resistance theor}^*

I will now sum up this rather lengthy discussion.
The two theories of ganglionic action may be
stated antithetically thus : in both theories the
accumulation of energy by ganglia is supposed to
be a continuous process; but while the resistance
theory supposes the rhythm to be exclusively due
to an intermittent and periodic discharge of this
accumulated energy on the part of the ganglionic
tissues, the exhaustion theory supposes that the
rhythm is largely due to a periodic process of
exhaustion and recovery on the part of the respond-

* The evidence, however, is not aUoorefher exclusive of the
resistance theory, for it is quite possible that in addition to the
hi^h irritability of the manubrium there may be conductile lines
of low resistance connecting this organ with the marginal ganglia.
I entertain this supposition because, as explained in my Eoyal
Society papers, I see reason to believe that the natural swimming
movements of Sai'sia are probably in part due to an intermittent
discharge of the ganglia. I think, therefore, that in this par-
ticular case the ganglia supply a tolerably constant stimulation
to the manubrium, while it is only at intervals that their energy
overflows into the bell, and that the higher degree of irritability
on the part of the manubrium ensures the tonic response of this
organ at a small cost of nervous energy. How far the rhythm of
the nectocalyx is to be attributed to the resistance mechanism of
the ganglia, and how far to the alternate exhaustion and recovery
of the contractile tissues, I think it is impossible to determine,
seeing that it is impossible exactly to imitate the natural gan-
glionic stimulation by artificial means. But it is, I think, of
importance to have ascertained at least this much, that in Sarsia
the tonus of one organ and the rhythm of another, which appa-
rently both received their stimulation from the same ganglia,
must at any rate in part be attributed to a differential irrita-
bility of these organs, as distinguished from their dilierent ial
stimulation.

ARTIFICIAL RHYTHM. 211

ing tissues. Now, I submit that my experiments
have proved the former of these two theories inade-
quate to explain all the phenomena of rhythm as
it occurs in the Medusae ; for these experiments
have shown that even after the removal of the
only ganglia which serve as centres of natural
stimulation, the excitable tissues still continue to
manifest a very perfect rhythm under the influence
of any mode of artificial stimulation (except heat),
which is of a constant character and of an inten-
sity sufficiently low not to produce tetanus. And
as 1 have proved that the rhythm thus artificially
produced is almost certainly due to the alternate
process of exhaustion and recovery which I have
explained, there can scarcely be any doubt that in
the natural rhythm this process plays an important
part, particularly as we find that temperature and
gases exert the same influences on the one rhythm
as they do on the other. Again, as an additional
reason for recognizing the part which the con-
tractile tissues probably play in the production of
rhythm, I have pointed to the fact that in the great
majority of cases in which rhythmic action occurs
the presence of ganglia cannot be suspected. For
it is among the lower forms of life, where ganglia
are cei-tainly absent, and where the functions of
stimulation and contraction appear to be blended
and diffused, that rhythmic action is of the most
frequent occurrence; and it is obvious with how
much greater difficulty the resistance theory is here
beset than is the one I now propose. Granted a
dififused power of stimulation with a diffused power

212 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

of response, and I see no essential difference between
the rhythmic motions of the simplest organism and
those of a deganglionated Medusa in acidulated
water. Lastly, the facts relating to the tonus of the
manubrium in Sarsia furnish very striking, and I
think almost conclusive, proof of the theory which
I have advanced.

CHAPTER IX.

POISONS.

1. Chloroform. — My observations with regard to
the distribution of nerves in Sarsia led me to in-
vestio-ate the order in which these connections aie
destroyed, or temporarily impaired, by amiesthetics.
The results, I think, are worth recording. In
Sarsia the following phases always mark the
progress of antesthesia by chloroform, etc. — 1. Spon-
taneity ceases. 2. On now nipping a tentacle,
pulling the manubrium, or irritating the bell, a
single locomotor contraction is given in answer to
every stimulation. (In the unan?esthesiated animal
a series of such contractions would be the result of
such stimulation.) 3. After locomotor contractions
can no longer be elicited by stimuli, nipping a
tentacle or the margin of the bell has the effect of
causing the manubrium to contract. 4. After stimu-
lation of any part of the nectocalyx (including
tentacles) foils to pi-oduce response in any part of
the or^fanism, the manubrium will continue its re-
sponse to stiumli ap[)lied directly to itself.

2. Nitrite of Aniyl. — On Sarsia the effect of this
15

214 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

agent is much the same as that of chloroform — the
description just given being quite as applicable to
the effects of tlie nitrite as to those of chloroform.
Before the loss of spontaneity supervenes, the rate
of the rh^^thm is increased, while the strength of
the pulsations is diminished.

Tiaropsis diademata, from the fact of its present-
ing a very regular rhythm and being but of small
size, is a particularly suitable species upon which
to conduct many experiments relating to the effect
of poisons. On this species the nitrite in appro-
priate (i.e. in very small) doses first causes irregularity
and enfeeblement of the contractions, together with
quickening of the rhythm. After a short time,
a gradual cessation of the swimming motions be-
comes apparent — these motions dying out more
gradually, for example, than they do under the
influence of chloroform. Eventually each pulsation
is marked only by a slight contraction of the
muscular tissue in the immediate neighbourhood of
the margin. If the dose has been stronger, however,
well-marked spasmodic contractions come on and
obliterate such gradual working of the poison. In
all cases irritability of all parts of the animal
persists for a long time after entire cessation of
spontaneous movements — perhaps for three or four
minutes in not over-poisoned animals ; but eventu-
ally it too disappears. On being now transferred
to noi'inal sea- water, the process of recovery is
slower than it is after ansesthesiation by chloroform.
It is interesting, moreover, to observe, that just as
the power of co-ordination was the first thing to be

POISONS. 215

affected by the nitrite, so it is the last thing to
return during recovery.

3. Caff tin. — The eilects of caffein on Sarsia may
be best studied by immersing the animals in a
saturated sea-water solution of the substance. In
such solutions the Medusi^ float to the surface, in
consequence of their lower specific gravity. I
therefore used shallow vessels, in order that the
margins of the nectocalyces might rest in the level
of the water that was thoroughly saturated. The
immediate effect of suddenly immersing Sarsia in
such a solution is very greatly to increase the rate
of the pulsations, and, at the same time, to diminish
their potency. The appearance presented by the
swimmino- motions is therefore that of a flutterinof
nature ; and such motions are not nearly so effectual
for progression as are the normal pulsations in
unpois;<ned water. This stage, however, only lasts
for a few seconds, after which the spontaneous
motions begin gradually to fade away. Soon they
altogether cease, though occasionally one among
a number of Sarsioe confined in the same saturated
solution will continue, even for several minutes
after the first immersion, to give one or two very
feeble contractions at long intervals. Eventually,
however, all spontaneity ceases on the part of all
the specimens, and now the latter will continue for
a very long time to be sensitive to stimulation. At
first severed feeble locomotor contractions will be
given in response to each stimulus ; and as on the
one hand these contractions never originate spon-
taneously, while, on the other hand, paralyzed

21G JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

SarsiiB never respond to a single stimulus with
more than a single contraction, these multiple
responses must, I think, be ascribed to a state of
exalted reflex irritability. After a long exposure
to the poison, however, only a single response is
given to each stimulus ; and still later all irritability
ceases. On now transferring the Sarsise to un-
poisoncd water, recovery is effected even though
the previous exposure has been of immensely long
duration, e.g. an hour.

An interesting point with regard to caffein-
poisoning of Sarsia is, that as soon as spontaneity
ceases the tentacles and manubrium lose their tonus
and become relaxed to their utmost extent. This
is not the case with an^sthesiation by chloroform,
even when pushed to the extent of suspending
irritability. If, however, Sarsise which have been
auDOsthesiated to this extent in chloroform be
suddenly transferred to a solution of caffein, the
tentacles and manubrium may soon be seen to relax,
and eventually these organs lose their tonus as
completely as if the anaesthesia had from the first
been produced by the ca'Iein. Moreover in this
experiment the irritaljility, which had been de-
stro^^ed by the chloroform, returns in the solution
of caiFijin — provided the latter be not quite satu-
rated— though spontaneity of course remains sus-
pended throughout.

The eifects of graduating the doses of caffein may
be stated in connection with another species, viz.
Tiaropsis diademata. In a weak solution the effects
are a quickening of the pulsations (e.g. from C4 to

POISONS. 217

120 per minute) together with a lessening of their
force. On sliglitly increasing the dose, the pulsa-
tions become languid, and prolonged pauses super-
vene. If the dose is again somewhat strengthened,
the pulsations become weaker and weaker, till they
eventually cease altogether. The animal, however,
is now in a condition of exalted reflex irritability ;
for its response to a single stimulus consists not
merely, as in the unpoisoned animal, of a single
spasm, but also, immediately after this, of a series
of convulsive movements somewhat resembling
swimming movements destitute of co-ordination.
If the strength of the solution be now again
increased, a stage of deeper ansesthesiation may be
produced, in which the Medusa will only respond
to each stimulation by a single spasm. In still
stronger solutions, the only response is a single
feeble contraction ; while in a nearly saturated
solution the animal does not respond at all. But
even from a saturated solution Tiaropsis diade-
mata will recover when transferred to unpoisoned
water.

4. Strychnia. — The species of covered-eyed Medusa
which I shall choose for describing the action of
strychnia is C^'anasa capillata, which is most admir-
ably adapted for experiments with this and some
of the other alkaloid poisons, from the fact that in
water kept at a constant temperature its pulsa-
tions are as regular as are those of a heart. After
Cyana^a capillata has been allowed to soak for ten
minutes or so in a weak sea-water solution of
strychnia, unmistakable signs of irregularity in the

218 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

pulsations supervene. This irregularity then in-
creases more and more, till at length it groAvs into
well-marked convulsions. The convulsions manifest
themselves in the form of extreme deviations from
the rhythmical contractions so characteristic of
Cyan?ea capillata. Instead of the heart-like regu-
larity with which systole and diastole follow one
another in the unpoisoned animal, we now have
periods of violent and prolonged systole resembling
tonic spasm ; and when the severity of this spasm
is for a moment abated, it is generally renewed
before the umbrella has had time a!2'-ain to become
fully expanded. Moreover, the spasm itself is not
of uniform intensity throughout the time it lasts ;
but while the umbrella is in a continuously
contracted state, there are observable a perpetual
succession of extremely irregular oscillations in the
strength of the contractile influence. It is further
a highly interesting fact that the convulsions are
very plainly of a iiaroxysvial nature. After the
umbrella has suffered a prolonged period of con-
vulsive movements, it expands to its full dimensions,
and in this form remains for some time in a state
of absolute quiescence. Presently, however, another
paroxysm supervenes, to be followed by another
])eriod of quiescence, and so on for hours. The
periods of quiescence are usually shorter than are
those of convulsion; for while the former seldom
last more than forty seconds or so, the latter may
continue uninterruptedly for live or six minutes. In
short, Medusce, when submitted to the influence of
str^'chnia, exhibit all the syinptoms of strychnia

POISONS. 219

poisoning in the higher animals. Death, however,
is always in the fully expanded form.

It seems desira})le to supplement these remarks
with a few additional ones on the effects of this
poison on the naked-eyed Medusoe. In the case of
Sarsia the symptoms of strychnia poisoning are not
well marked, from the fact that in this species
convulsions always take the form of locomotor
contractions. The symptoms, however, are in some
respects anomalous. They are as follows. First
of all the swimming motions become considerably
accelerated, periods of quiescence intervening be-
tween abnormally active bouts of swimming.
By-and-by a state of continuous quiescence comes
on, during which the animal is not responsive to
tentacular irritation, but remains so to direct
muscular irritation, giving one response to each
direct stimulus. The tentacles and manubrium are
much relaxed. In a sea- water solution just strong
enough to taste bitter, this phase may continue for
hours ; in fact, till a certain opalescence of the con-
tractile tissues — which it is a property of strychnia,
as of most other reagents, to produce — has ad-
vanced so far as to place the tissues beyond recovery.
If the exposure to such a solution has not been very
prolonged, recovery of the animal in normal water
is rapid. In a specimen exposed for two and a half
hours to such a solution, recovery began in half an
hour after restoration to normal water, but was never
complete. In all cases, if the poisoning is allowed
to pass beyond the stage at Avhich response to direct
muscular irritation ceases, the animal is dead.

220 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

On Tiaropsis indicans this poison has the effect
of causing a general spasm, Avhich would be undis-
tinguishable from that which in this species results
from general stimulation of any kind, were it not
that there is a marked difference in one particular.
For in the case of strychnia poisoning, the spasm,
while it lasts, is not of uniform intensity over all
parts of the nectocalyx ; but now one part and now
another part or parts are in a state of stronger
contraction than other parts, so that, as a general
consequence, the outline of the nectocalyx is con-
tinually changing its form. Moreover, in addition
to these comparatively slow movements, there is a
continual twitching observable throughout all parts
of the nectocalyx. Each individual twitch only
extends over a small area of the contractile tissue ;
but in their sum their effect is to throw the entire
organ into a sort of shivering convulsion, which is
superimposed on the general spasm. After a time
the latter somewhat relaxes, leaving the former
still in operation, which, moreover, now assumes a
paroxysmal nature — the convulsions consisting of
strong shudders and frequent spasms with occasional
intervals of repose.

In the case of Tiaropsis diademata the action of
strychnia is very similar, with the exception that
there is no continuous spasm, although occasional
ones occur amid the twitching convulsions. After
a time, however, all convulsions cease, and the
animal remains quiescent. While in this condition
its reflex excitability is abnormally increased, as
shown by the fact that even a gentle touch will

POISONS. 221

bring on, not merely a single responsive spasm, as
in the impoisoned animal, but a whole series of
successive spasms, which are often followed by a
paroxysm of twitching convulsions. The condition
of exalted reflex irritability is thus exceedingly
well marked. Recovery in normal water at this
stage is rapid, the motions being at first characterized
by a want of co-ordination, which, however, soon
passes off.

5. Veratriiirti. — In Sarsia the first effect of this
poison is to increase the number and potency of the
contractions; but its later effect is just the con-
verse, there being then prolonged periods of quies-
cence, broken only by very short swimming bouts
consisting of feeble contractions. The feebleness
of the contractions gradually becomes more and
more remarkable, until at last it is with great
difficulty that they can be perceived at all ; indeed,
the progressive fading away of the contractions
into absolute quiescence is so gradual that it is
impossible to tell exactly when they cease. During
the quiescent stage the animal is for the first time
insensible both to tentacular and to direct stimula-
tion of the contractile tissues. That the gradual
dying out of the strength of the contractions is not
altogether due to the progressive advance of central
paralysis, would seem to be indicated by the fact
that contractions in response to direct stimulation
of the con Tactile tissues are no more powerful, at
any given stage of the poisoning, than ai"e either
responses to tentacular stimulation or the spon-
taneous contractions. Still, as we shall immediately

222 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

sec, in the various species of Tiaropsis, irritability
persists after cessation of the spontaneous contrac-
tions. In Sarsia the nervous connections between
the tentacles and manubrium, and also between the
tentacles themselves, are not impaired during the
time that the bell is motionless ; and even when
the irritability of the bell has quite disappeared as
regards any kind of stimulation, the manubrium
and tentacles will continue responsive to stimuli
applied either directly to themselves or to any
part of the neuro-muscular sheet of the bell.

The convulsions due to the action of veratrium
are well marked in the various species of the genus
Tiaropsis. They consist of violent fluttering
motions without any co-ordination ; but there are
no spasms, as in the case of strychnia poisoning.
After the convulsions have lasted for some time, a
quiescent stage comes on, during which the animal
remains responsive to stimulation, though not ab-
normally so. Recovery in unpoisoned water is
rapid, the movements being at first marked by an
absence of co-ordination.

6. Digitalin. — The first effect of this poison on
Sarsia is to quicken the swimming motions, and
then to enfeeble them progressively till they degene-
rate into mere spasmodic twitches. The manubrium
and tentacles are now strongly retracted, while the
nectocalyx is drawn together so as to assume an
elongated form. The latter is now no longer respon-
sive either to tentacular or to direct stimulation;
but the tentacles and manubrium both remain
responsive to stimuli applied either directly to

POISONS. 223

themselves or to the neiiro-muscular tissue of the
bell. Death always takes place in very strong
systole ; and as this is an exceedingly unusual thing
in the case of Sarsia, there can be no doubt that,
in this respect, the action of the digitalin is ditferent
on the MedusD3 from what it is on the heart.

On the various species of Tiaropsis, digitalin at
first causes acceleration of the swimming move-
ments, with great irregularity and want of co-
ordination. Next, strong and persistent spasms
supervene, which give the outline of the necto-
calyx an irregular form ; and every now and then
this unnatural spasm gives place to convulsive
SAvimming motions. Evidently, however, the spasm
becomes quite persistent and excessively strong.
The manubrium of Tiaropsis indicans crouches to
its utmost, and the animal dies in strong systole.

7. Atropin. — In the case of Sarsia atropin causes
convulsive swimming motions. The systoles next
become feeble, and finally cease. The nectocalyx
is now somewhat drawn together in persistent
systole, with the manubrium and tentacles strongly
retracted. Muscular irritability remains after ten-
tacular irritability has disappeared, but it is then
decidedly enfeebled.

In the various species of Tiaropsis the convulsions
are strongly pronounced. They begin as mere
accelerations of the natural swimming motions,
but soon grow into well-marked convulsions, con-
sisting of furious bouts of irregular systoles follow-
ing one another with the utmost rapidity, and
wholly without co-ordination. Occasionally these

224 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

movements are interrupted by a violent spasm,
on which strong shuddering contractions are super-
imposed.

8. Nicotin. — On dropping Sarsia into a sea-water
solution of nicotin of appropriate strength, the
animal iuimediately goes into a violent and con-
tinuous spasm, on which a number of rapidly suc-
ceeding minute contractions are superimposed.
The latter, however, rapidly die away, leaving the
nectocalyx still in strong and continuous systole;
tentacles and manubrium are retracted to the
utmost. Shortly after cessation of spontaneity,
the bell is no longer responsive to tentacular stimu-
lation, but remains for a considerable time respon-
sive to direct stimulation of its own substance;
eventually, however, all irritability disappears,
while the tentacles and manubrium relax. On
transferring tlie animal to normal w^ater, muscular
irritability first returns, and then central, as shown
by the earlier response of the bell to direct than to
tentacular stimulation ; but if the animal has been
poisoned heavily enough to have had its muscular
iri'itability suspended, it is a long time before
central irritability returns. Soon after central
irritability has returned, the animal begins to shoAV
feeble signs of spontaneit}^ the motions being
exceedingly weak, with long intervals of repose ;
but the degree of such feebleness depends on the
length of time during wdiich the animal has pre-
viously been exposed to the poison ; thus in a speci-
men which had been removed from the poison
immediately after the disappearance of reflex

POISONS. 225

irritability had supervened, recovery began in ten
minutes after rc-iunnersion, and was cumplete in
lialf an Lour.

In Tiaropsis the symptoms of nicotin poisoning
are also well marked. When gradually adminis-
tered, the first effect of the narcotic is a complete
loss of co-ordination in the swimming motions. A
sli!_dit increase of the dose brino-s about a tonic
spasm, which differs from the natural spasm of
these animals — (a) in being stronger, so that the
nectocalyx becomes bell-shaped rather than square,
(b) in being much more persistent, and (c) in under-
going variations in its intensity from time to time,
instead of being a contraction of uniform strength ;
thus the spasm temporarily affects some parts of
ijke nectocalyx more powerfully than other parts,
so that the organ may assume all sorts of shapes.
Such distortions proceed even further under the
influence of nicotin than under that of strychnine,
etc. Sometimes, for instance, one quadrant will
project in the form of a pointed promontory; at
other times two adjacent or opposite quadrants
will thus project, and occasionally all four will do
so, the animal thus becoming star-shaped. Some-
times, again, one quadrant will be less contracted
than the other three, while at other times more or
less slight relaxations affect numerous parts of the
bell, its margin being thus rendered sinuous, though
more or less violently contracted in all its parts.
This state of violent spasm lasts for several minutes,
when it gradually passes off, the nectocalyx relaxing
into the form of a deep bowl and remaining quite

226 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

passive, except that every now and then one part
or another of the margin is suddenly contracted in
a semilunar form. By-and-by, however, even these
occasional twitches cease, and the animal is now
insensible to all kinds of stimulation. Recovery in
noi-mal water is gradual, and marked in its first
stage by the occasional retractions of the margin
last mentioned. At about this stage also, or some-
times slightly later, the animal first becomes respon-
sive to stimulation ; and it is interesting to note
that the response is performed, not by giving a
general spasm as would the unpoisoned animal, but
by folding in the part irritated — an action which
very much resembles, on the one hand, the spon-
taneous couA^ulsive movements just described, and,
on the other, the response which is given to stimu-
lation by the unpoisoned bell when gently irritated
after removal of its margin. After these stages
there supervenes a prolonged period of quiescence,
during which the animal remains normally respon-
sive to stimulation. Spontaneity may not return
for several hours, and, after it does return, the
animal is in most cases permanently enfeebled.
Indeed, on all the species of Medusre, nicotin, both
during its action and in its subsequent effects, is
the most deadly of all the poisons I have tried.

9. Morphia. — The anjiesthesiating effects of mor-
phia are as decided as are those of chloroform. I shall
confine myself to describing the process of an53esthe-
siation in the case of Aurelia aurita in an extract
from my notes. "A very vigorous specimen, having
twelve lithocysts, was placed in a strong sea-water

POISONS. 227

sohition of morphia. Half a minute after being
introduced connuencemcnt of torpidity ensued,
shown by contractions becoming fewer and feebler
In one minute the feeble impulses emanating from
the prepotent lithocyst failed to spread far through
the contractile tissue, appearing to encounter a
growing resistance. Eventually this resistance
became so great that only a very small portion of
contractile tissue in the immediate neighbourhood
of the lithocyst contracted, and this in a very slow
and feeble way. Two minutes after immersion
even these partial contractions entirely ceased, and
soon afterwards all parts of the animal w^ere com-
pletely dead to stimulation. Recovery in normal
water slower than that after chloroform, but still
soon quite complete. Repeated experiment on this
individual four times without injury."

10. Alcohol. — The solution must be strong^ to
cause complete intoxication. The first effect on
Sarsia is to cause a great increase in the rapidity
of the swimming motions — so much so, indeed, that
the bell has no time to expand properly between
the occurrence of the successive systoles, which, in
consequence, are rendered feeble. These motions
gradually die out, leaving the animal quite motion-
less. The nectocalyx is now responsive to stimuli
applied at the tentacles, and sometimes two or
three contractions will follow such a stimulus, as if
the spontaneity of the animal were slightly aroused
by the irritation. Soon, however, only one contrac-
tion is given in response to every tentacular irrita-
tion, and by-and-by this also ceases — the Medusa

228 JELLY-FISH, STAR-FISH, AND SEA-URCHINS,

being thus no longer responsive to central stimula-
tion. It remains, liowever, for a long time responsive
to stimulation of the neuro-muscular sheet ; indeed,
the strength of the alcohol solution must be very
considerable before loss of muscular irritability
supervenes. It may thus be made to do so, how-
ever; and on then transferring the animal to normal
water, recovery begins in from three minutes to a
quarter of an hour. The first contractions are very
feeble, with long intervals of repose ; but gradually
the animal returns to its normal state.

The above remarks apply also to Tiaropsis. In
Tiaropsis indicans the manubrium recovers in normal
water sooner than the nectocalyx. Both in Sarsia and
Tiaropsis the manubrium and tentacles are retracted
while exposed to alcohol, and, after transference to
normal sea-water, the animals float on the surface,
presumably in consequence of their having imbibed
some of the spirit. The period during which flota-
tion lasts depends, {a) on the strength of the alcohol
solution used, and (6) on the time of exposure to its
influence. It may last for an hour or more ; but in
no case is recovery complete till some time after the
flotation ceases.

11. Curare. — Curare had already been tried npon
Medus?e, and was stated to have produced no eflfects ;
it is therefore especially desirable that I should
first of all describe the method of exhibiting it
which I employed.

Having placed the medusa to be examined in a
flat-shaped beaker, I filled the latter to overflowing
with sea-water. 1 next placed the beaker in a

POISONS. 229

large Imsln, into which I then poured sea-water
until the level was the same inside and outside the
breaker, i.e. until the two bodies of water all but
met over the brim. Having divided the medusa
across its whole diameter, with the exception of a
small piece of marginal tissue at one side to act as
a connecting link between the two resulting halves,
I transferred one of these halves to the water in the
basin, leaving the other half still in the beaker —
the marginal tissue which served to unite the two
halves being thus supported by the rim of the
beaker. Over the minute portion of the marginal
tissue which was thus of necessity exposed to the
air, I placed a piece of blotting-paper which dipped
freely into the sea- water. Lastly, I poisoned the
water in the beaker with successive doses of curare
solution.

The results obtained by thi,s method were most
marked and beautiful. Previous to the adminis-
tration of the poison both halves of the medusa
were of course contracting vigorously, waves oi
contractile influence now running from the half in
the beaker to the half in the basin, and now vice
versa. But after the half in the beaker had become
effectually poisoned by the curare, all motion in it
completely ceased, the other, or unpoisoned half,
continuing to contract independently. I now
stimulated the poisoned half by nipping a portion
of its margin with the forceps. Nothing could be
more decided than the result. It will be remem-
bered that when any part of Staurophora laciniata
is pinched with the forceps or otherwise irritated,

16

280 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

the motion of the whole body which ensues is
totally dilierent from that of an ordinary locomotor
conu^action — all parts folding together in one very
strong and long-protracted systole, after which the
diastole is very much slower than usual. Well, on
nipping any portion of the poisoned half of Stau-
rophora laciniata, this half remained absolutely
motionless, while the unpoisoned half, though far
away from the seat of irritation, immediately ceased
its normal contractions, and folded itself together in
the very peculiar and distinctive manner just de-
scribed. This observation was repeated a number
of times, and, when once the requisite strength of
the curare solution had been obtained, always with
the same result. The most suitable strenoth I found
to be 1 in 2500, in which solution the poisoned half
required to soak for half an hour.

I also tried the effect of this poison on the covered-
eyed Medusje, and have fairly well satisfied myself
that its peculiar influence is likewise observable in
the case of this group, although not in nearly so
well-marked a manner.

It has further to be stated that when the poisoned
half is ao'ain restored to normal sea-water, the effects
of curare pass olf with the same rapidity as is
observable in the case of tlie other poisons which
1 have tried. Thus, although an exposure of hall
an hour to the influence of curare of the strength
named is requisite to destroy the motor power in
the ease of Staurophora laciniata, half a minute is
sufficient to ensure its incipient return when the
animal is again immersed in unpoisoned water.

POISONS. 231

It is also to be observed that a very slight degree
of over-poisoning paralyzes the transmitting system
as well as the responding one ; so that if any one
should repeat my observaticm, I must warn him
ajfainst drawinor erroneous conclusions from this
fact. Let him use weak solutions with prolonged
soaking, and by watching when the voluntary
motions in the poisoned half first cease, he need
experience no difficulty in obtaining results as
decided as it is possil)le for him to desire.

12. Cyanide of Potassium. — On Sarsia the first
effect is to quicken the contractions and then to
enfeeble them. The animal assumes an elongated
form, as already described under atropin. Spon-
taneity ceases very rapidly even in weak solutions ;
and for an exceedingly short time after it has done
so, the bell continues responsive both to tentacular
and to direct stimulation. For a long time after
the bell ceases to respond to any kind of stimula-
tion, the nervous connections between the tentacles
and between the tentacles and manubrium remain
intact, as also do the nervous connections of these
organs with all parts of the bell. This interesting
fact is rendered apparent, first, by stimulating a
tentacle and observing that all the four tentacles
and the manubrium respond ; and, second, by irri-
tating any part of the neuro-muscular sheet of the
bell, and observing that while the latter does not re-
spond both the tentacles and the manubrium retract.
Recovery from this stage occupies several hours.

In the case of Tiaropsis the convulsions are, as
usual, more pronounced, being marked by the occur-

232 JELLY-FISH, STAR-FISH, AND SEA- URCHINS.

rence of a gradually increasing spasm, which differs
from a normal spasm in the respects already de-
scribed under stryclmia. In all the species both of
Sarsia and Tiaropsis, the manubrium and tentacles
are retracted during exposure to this poison.

BeriiarJcs.

The above comprises all the poisons which I have
tried, and I think that all the observations taken
too'ether show a wonderful des^ree of resemblance
between the actions of the various poisons on the
Med usee and on the hio-her animals — a c^eneral fact
which is of interest, when we remember that in
these nerve-poisons we possess, as it were, so many
tests Avherewith to ascertain whether nerve-tissue,
where it first appears upon the scene of lif'e, presents
the same fundamental properties as it does in the
hiojher animals. And these observations show that
such is the case. When the physiologist bears in
mind that in Sarsia w^e have the means of testing
the comparative inlluence of any poison on the
central, peripheral, and muscular systems respec-
tively,* he will not fail to appreciate the signifi-
cance of these observations. In reading over the
whole list he will meet with an anomaly here and

* The method of comparison consists, as will already have been
gather-ed from the perusal of the foregoing sections, in : — fir.-t,
sl.iinnlating the tentacles, and observing whether this is followed
by such a discharge of the attached ganglion as causes tlie bell to
contract ; next, stimulating the bell itself, to ascertain whether
the muscular irritability is impaired ; and, lastly, stimulating
either the tontacles or the bell, to observe whether the reciprocal
connections between tentacles, bell, and manubrium arenuiiiiured.

POISONS. 233

there; but, on the whole, I do not think he can
fail to be satisfied with the wondeiTully close adher-
ence which is shown by these elementary nervous
tissues to the rules of toxicology that are followed
by nervous tissues in general. In one respect,
indeed, there is a conspicuous and uniform devia-
tion from these rules ; for we have seen that in the
case of every poison mentioned more or less com-
plete recovery takes place when the influence of the
poison has been removed, even though this has
acted to the extent of totally suspending irritability.
In other Avords, there is no poison in the above list
Avliich has the property, when applied to the Medus?e,
of destroying life till long after it has destroyed
all signs of irritability. What the cause of this
uniform peculiarity may be is, of course, conjectural;
but I may suggest two considerations which seem
to me in some measure to mitigate the anomaly.
In the first place, we must remember that in the
Medusa there are no nervous centres of such vital
importance to the organism that any temporary
suspension of their functions is followed by im-
mediate death. Therefore, in these animals, the
various central nerve-poisons are at liberty, so to
speak, to exert their full influence on all the ex-
citable tissues without having the course of their
action interrupted by premature death of the organ-
ism, which in higher animals necessarily follows the
early attack of the poison on a vital neiwe-centre.
Again, in the second place, we must remember that
the method of administering the above-mentioned
poisons to the Medusae was very different from

234 JELLY-FISU, STAR-FISH, AND SEA-URCHINS.

that which we employ when administering them to
other animals ; for, in the case of the Medusie, the
neuro-muscular tissue is spread out in the form of
an exceedingly tenuous sheet, so that when the
animal is soaking in the poisoned water every por-
tion of the excitable tissue is equally exposed to its
influence ; and that the action of a poison is greatly
modified by such a difference in the mode of its
administration has been proved by Professor Gamgee,
who found that when a frog's muscle is allowed
to soak in a solution of vanadium, etc., it loses
its irritability, while this is not the case if the poison
is administered by means of the circulation.

I may farther observe that in the case of all
poisons I have tried, the time required for recovery
after the animal is restored to normal water varies
immensely. The variations are chiefly determined
by the length of time during which the animal has
been exposed to the influence of the poison, but
also, in a lesser degree, by the strength of the solu-
tion enployed. To take, for instance, tlie case of
caffein or chloroform, if Sarsicie are transferred to
normal water after they first cease to move, a few
seconds are enough to restore their spontaneity;
wdiereas, if they are allowed to remain in the
poisoned water for an hour, they may not move
for one or two hours after their restoration to un-
poisoned water. In consequence of such great varia-
tions occurring from these causes, I was not able
to compare the action of one poison with that of
another in respect of the time required for effects
of poisoning to pass away.

POISONS. 235

I shall conclucle all I have to say upon the subject
of poisons by stating the interesting fact, that if
any of the narcotic or anfiesthesiating agents be
administered to any portion of a contractile strip
cut from the umbrella of Aurelia aurita in the way
already described, the rate of the contraction-waves
is first progressively slowed, and eventually their
passage is completely blocked at the line where the
poisoned water begins. Upon now restoring the
poisoned portion of the contractile strip to normal
sea-water the blocking is gradually overcome, and
eventually every trace of it disappears.*

Tlie contractile wave may be blocked by poisons
in another way. A glance at Fig. 11 will show
that a circumferential strip cut from the umbrella
of Aurelia aurita is pervaded transversely by a
number of nutrient tubes, which have all been cut
through by the section. At the side of the strip,
therefore, fuithest from the margin there are situ-
ated a number of open ends of these nutrient tubes.
Now, on injecting any of the narcotic poisons into

* In conductincr this experiment, care must be taken not to exert
the slightest pressure on any part of the strip. The method I
adopted, therefore, was to have a vessel with a very deep furrow
on each of its opposite lips. Upon filling this vessel to the level
of these furrows with the poisoned water, and then immersing
the whole vessel in ordinary sea- water up to the level of its brim,
some of the poisoned water of course passed through the open
furrows. The external body of water {i.e. the normal sea-water
containing the animal) was therefore made proportionally very
large, so that the slight escape of poison into it did not affect
the experiment. On now passing the portion of the strip to be
poisoned throngh the opposite furrows, it was allowed to soak in
the poison while freely fit ating, and so without suffering pressui-e
in any of its parts.

236 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

one of these open enrls, the fluid of course permeates
the ^vhole tube, and the contraction-wave becomes
blocked at tlie transverse line occupied by the tube
as effectually as if the contractile strip had been cut
through at that line.

A glance at Fig 10, again, will show that each
lithocyst is surrounded by one of these nutrient
tubes. Upon injecting this tube, therefore, in a
contractile strip, the effect of the poison may be
exerted on the lithocyst more specially than it
could be by j-ny other method of administration.
In view of recent observations concerning the effects
of curare on the ccntial nervous masses of higher
animals, it may be worth while to state that a dis-
charging lithocyst of Aurelia aurita, when thus
injected with curare, speedily ceases its discharges.
This fact alone, however, would not warrant any
very trustworthy conclusions as to the influence of
curare upon discharging centres ; for it is not im-
probable that the paralyzing effects may here be
due to the influence of the poison on the surround-
inor contractile tissue.

o

It is interesting to observe that if the discharging
lithocyst be injected with chloroform, or a not too
strong solution of morphia, it recovers in the course
of a ni'dit. With alcohol the first effects of , the in-
jection are considerably to accelerate the frequency
and to augment the potency of the discharges; but
the subsequent effects are a gradual diminution in
the frequency and the vigour of these discharges,
until eventually total quiescence supervenes. In the
course of a few hours, however, the torpidity wears

POISONS. 237

away, and finally the medusa returns to its normal
state.*

* Since the above results on the effects of poisons were pub-
lished in my Royal Society papers, Dr. Krukenberg has couducted
a research upon " comparative toxicology," in which he has de-
voted the larger share of his attention to the Medusae. While
expressing my gratification that when he adopted my methods he
succeeded iu confirming my results, I may observe that the
criticism which he somewhat bluntly passes upon the latter is not
merely unwarranted, but based upon a strange misconception of
a well-known principle in the physiology of nerves and muscles.
This criticism is tliat these results as published by me are
worthless and *'a dead chapter in science," because I failed to
prove that it was the nervous (as distinguished from the muscular)
elements which were effected by the various poisons. In his
opinion this distinction can only be made good by employing
electrical stimulation upon the sub-umbrella tissue when this has
lost its spontaneity under the influence of poisons : if a response
ensues wliich does not ensue when the tissue is stimulated
mechanically, he regards the fact as proof that the muscular
tissue remains unaffected while the nervuus tissue has been
rendered functionless.

Now, in the first place, I have here to show that there is, as I
have said, a fundamental error touching a well-known principle of
physiology. So far as there is any difference between the ex-
citability of nei"ve and muscle with respect to mechanical and
electrical stimulation, it is the precise converse of that which Dr.
Krukenberg supposes ; it is not muscle, but nerve, which is the
more sensitive to electrical stimulation — by which I understand
him to moan the induction shock. The remarkable transposition
of Dr. Krukenberg's ideas upon this matter does not affect the
results of his observations upon tlie action of the various poisons;
it only renders fatuous his criticisai of these same results as
previously published by me.

In the next place, I have to observe that in all my experiments
I tried, as he subsequently tried, both kinds of stimulation, and
also the constant current; but I soon found that even when one
went to work with one's ideas upon the subject in a non-inverted
position, no trustworthy inference could be drawn in favour of
the muscular clcaicuts alone remaining uninjured from the bare

238 JELLY-FISH, STAR-FISH, AND SEA-UHCHINS.

Physiological Effects of Fresh Water on the Mecliiscc

As fresh water exerts a very deadly int^ucnce on
the MedusfB, this seems the most apj)ropriate place
for describing its action. Such a description has
already been given by Professor L. Agassiz, but it
is erroneous. He writes, "Taking up in a spoon-
ful of sea- water a fresh Sarsia in full activity, when
swimming most energetically, and emptying it into
a tumbler full of fresh water of the same tempera-
ture, the little animal will at once drop like a ball

fact that after the poisonino: the neuro-muscnlar tissue oftec
behaved diffi-rontly towards different kinds of stimulation.

Fui'ther, in the particular case of my experiments with curare —
against which Dr. Krukenberg's remarks are chiefly dii-ected on
the ground tliat I did not prove the paralysis to be a merely mus-
cular effect — I succeeded in obtaining very much better proof of
the poison acting on the nervous elements, to the exclusion of the
muscular, than I could have obtained by any process of inference,
however goot] ; that is to say, I obtained direct proof. It appears
to me that Dr. Krukenberg must have failed to understand the
English of the following sentences : " On nipping any portion of
the poisoned half of Staurophora laciniata, this half remained
absolutely motiotiless, while the uniioisoned half, ''hough far away
from the seat of irritation, innnediately ceased its normal con-
tractions, and folded itself together in the very peculiar and dis-
tinctive manner just described," i.e. "in one very strong and
long-protracted systole." For the rest, see note on page 232.

Lastly, while again expressing my satisfaction that on all
matters of fact our results are in full harmony, I may be allowed
to remark that in my opinion his deductions, as embodied in his
schema of the inferred innervation of Medusaj, are very far in
advance of anything that is justified by observation. (See, for
this elaborate schema, in which there are represented volitional,
motor, reflex, and inhibitory centres, as well as a clearly defined
system of sensory and motor nerves, " Vergleichend-Physio-
logogische SLudieu, diitte Abtheiling," p. 141 : Ilcidelberg, 1880.)

POISONS. 239

to the bottom of the glass and remain for ever
motionless — killed instantaneously by the mere
difference of the density of the two media." * As
regards the appeaiance presented by Sarsia Avhcn
subjected to " this little experiment," the account
just quoted is partly correct; but Professor Agassiz
must have been over-hasty in concluding that, be-
cause the aTiimals seemed to be thus " killed instan-
taneously," such was really the case. Nothing,
indeed, could be more natural than his conclusion ;
for not only is the contrast between the active
swimming motions of the Sarsia in the sea-water
and their cessation of all motion in the fresh water
very suggestive of instantaneous death ; but a shoi t
time after immersion in the latter their contractile
tissues, as Professor Agassiz observed, become
opalescent and whitish. Nevertheless, if he had
taken the precaution of again transferring the
Sarsia to sea- water, he would have found that the
previous exposure to fresh water had not had the
effect which he ascribes to it. After a variable
time his specimens would have resumed their swim-
ming motions ; and although these might have had
their vigour somewhat impaired, the animals would
have continued to live for an indefinite time — in
fact, quite as long as other specimens which had
never been removed from the sea-water. Even
after fivQ minutes' immersion in fresh water,
Sarsige will revive feebly on being again restored
to sea- water, although it may be two or three
hours before they do so ; they may then, how-
* *' Mem. American Acad. Arts and Sciences," 1800, p. 229.

240 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

ever, live as long as other specimens. In many
cases Savsiie will revive even after ten minutes'
exposure; bat tlie time required for recovery is
then very long, and the subsequent pulsations are
of an exceedingly feeble character. I never knew a
specimen survive an exposure of fifteen minutes.*
In not a few cases, after immersion in fresh water,
the animal continues to pulsate feebly for some little
time ; and, in all cases, irritability of the contractile
tissues peisists for a little while after spontaneity
has ceased. The opalescence above referred to
principally affects the manubrium, tentacles, and
margin of the nectocalyx. While in fresh w^ater
the manubrium and tentacles of Sarsia are strongly
retracted.

Thinking it a curious circumstance that the mere
absence of the few mineral substances w^hich occur in
sea-water should exert so profound and deadly an
influence on the neuro-muscular tissues of the
Medusa?, I was led to try some further experiments
to ascertain whether it is, as Agassiz affirms, to the
mere difference in density between the fresh and
the sea Avater, or to the absence of the particular
mineral suljstances in question, that the deleterious
influence of fresh water is to be ascribed. Although

* The covered-eyed MedusiB survive .a longer immersion than
the naked-eyed — Aiirelia aurita, for in.stauce, requiring from a
quarter to half an hour's exposure before being placed beyond
I'ecovery. Moreover, the cessation of spontaneity on the first
ioimersion is not so sudden as it is in tho case of the naked-eyed
Medusae — tlie pulsations continuing for about five minute?, during
which time they become weaker and weaker in so gradual a
rnauuer that it is hard to toll exactly when they first ceage.

POISONS. 241

my experiments lead to no very instructive con-
clusion, they are, I think, worth stating.

I first tried dissolving chloride of sodium in fresh
water till the latter was of the same density as sea-
water. Sarsiie dropped into such a solution con-
tinued to live for a great number of Ik urs ; but
they were conspicuously enfeebled, keeping for the
most part at the bottom of the vessel, and having
the vigour of their swimming motions greatly im-
paired. The tentacles and manubrium w^ere strongly
retracted, as in the case of exposure to fresh water,
and the tissues also became slightly opalescent.
Thinking that perhaps a fairer test would be only
to add as much chloride of sodium to the fresh
water as occurs in sea- water, I did so ; but the re-
sults were much the same. On now adding sulphate
of magnesium, however, to the amount normally
])resent in sea- water, the Sarsise became more active.
1 next tried the effects of chloride of sodium dis-
solved in fresh water to the point of saturation, or
nearly so. The Sarsi?e, of course, floated to the
surface, and they immediately began to show
vsymptoms of torpidity. The latter became rapidly
more and more pronounced, till spontaneity was
quite suspended. The animals, however, were not
dead, nor did they die for many hours, their irrita-
bility continuing unimpaired, although their spon-
taneity had so cinnpletely ceased. The tentacles and
manubrium were exceedingly relaxed, which is an
interesting fact, as being the converse of that which
occurs in water containing too small a proportion of
salt. Lastly, to give the density hypothesis a still

24-2 JELLY-FISH, STAR-FJSH, AND SEA-URCHINS.

more complete trial, I dissolved various neutral
salts and other substances, such as sugar, etc., in
fresh water till it was of the density of sea- water ;
but in all cases, on immersing Sarsine in such solu-
tions, death was as rapid as that which followed
theii- immersion in fresh water.

The Fresh-iuater Medusa.

On June 10, 18S0, it Avas noticed that the
fresh water in the large tank of the lily-house of
the Royal Botanical Society, Regent's Park, was
swarming with a small and active species of Medusa,
previously unknown to science — it being, indeed, at
that time unknown to science that any species of
Medusa inhabited fresh water, altliough it was well
known that some of the other Hydrozoa do so.
Examination showed that the new species belonged
to the order TrachomedusiB, and the Petasidsp of
Jfaeckel's classification — its nearest known relative,
according to Professor Ray Lankester, being the genus'
Aglauropsis, which occurs on the coast of Brazil.
The Medusa was called Limnocodium (Xijuvri, a
pond, and kw^wv, a bell) sorbii by Professors All"
man and Lankester. I am indebted to the kindness
of Professor Allman for permission to reproduce his
drawing of the animal. Fig. 31.) It is remark-
able that, although this J.Iedusa has reappeared
every June in the same tank, no one has yet suc-
ceeded in tracing its life-history. Nor is it known
from what source the tank first became impregnated
with this organism. No doubt the germs must

POISONS.

243

have been conveyed by the roots or leaves of some
tropical plant that at some time was placed in the

Fig. 31.

tank{ but the Botanical Society has no record of
any plant which can be pointed to as thus having
probably served to import the organism.

I shall now proceed to give an account of my

'2H JELLY-FISH, STAU-FJSH, AND SEA-URCHINS.

observations on the pliysiology of this interesting
animal, by quoting in extenso my original paper
upon the subject {Nature, June 24, 1880). Before
doing so, however, I may state that Professors A.
Agassiz, Moseley, and others have since informed us
that sundry species of sea- water Medusae have been
observed by them living and thriving in the brackish
waters of estuaries — a fact which strongly corrobo-
rates the inference at the end of the present paper.

" The natural movements of the Medusa precisely
resemble those of its maiine congeners. More par-
ticularly, these movements resemble those of the
marine species wdiich do not swim continuous^,
but indulge in frequent pauses. In water at the
temperature of that in the Victoria lily-house (85°
Fahr.), the pauses are frequent, and the rate of the
rhythm irregular, suddenly quickening and suddenly
slowing even during the same bout, which has the
effect of giving an almost intelligent appearance to
the movements. This is especially the case wdth
young specimens. In colder water {Qb° to 75°) the
movements are more regular and sustained; so
that, guided by the analogy furnished by my ex-
periments on the marine forms, I infer that the
temperature of the natural habitat of this Medusa
cannot be so high as that of the water in the
Victoria lily-house. In water of that temperature
the rate of the rhythm is enoimously high, some-
times rising to three pulsations per second. But
by progressively cooling the water, this rate may
be progressively lowered, just as in the case of the
marine species ; and in water at 65°, the maximum

POISONS. 245

rate that I have observed is eighty y)ulsatlons per
minute. As the temperature at which the greatest
activity is displayed by the fresh- water species is
a temperature so high as to be fatal to all the
marine species which I have observed, the effects
of cooling are, of course, only parallel in the two
cases when the effects of a series of higher tem-
peratures in the one case are compared with those
of a series of lower temperatures in the other.
Sirailarl}^, while a temperature of 70° is fatal to
all the species of marine Medusos which I have
examined, it is only a temperature of 100'' that is
fatal to the fresh- water species. Lastly, while the
marine species will endure an}' degree of cold with-
out loss of life, such is not the case with the fresh-
water species. Marine Medusip, after having been
frozen solid, Avill, when gradually thawed out, again
resume their swimming movements; but this fresh-
water Medusa is completely destro^^ed by freezing.
Upon being thawed out, the animal is seen to have
shrunk into a tiny ball, and it never again recovers
either its life or its shape.

" The animal seeks the sunlight. If one end of
the tank is shaded, all the Medusae cono-reoate at
the end which remains unshaded. Moreover, durino-
the daytime they swim about at the surface of the
water ; but when the sun goes down they subside,
and can no longer be seen. In all these habits
they resemble many of the sea-w^ater species. They
are themselves non-luminous.

*'I have tried on about a dozen specimens the

effect of excising ihe margin of the nectocalyx. In
17

246 JELLY-FISH, STAR-FISH, AND SEA-URCHIXS.

the case of all the specimens thus operated upon,
the result was the same, and corresponded precisely
with that which I have obtained in the case of
marine species ; that is to say, the operation pro-
duces immediate, total, and permanent paralysis of
the nectocalyx, while the severed margin continues
to pulsate for two or three days. The excitability
of a nectocalyx thus mutilated persists for a day or
two, and then gradually dies out, thus also resem-
bling the case of the marine naked-eyed MedusiB.
More particularly, the excitability resembles that
of those marine species which sometimes respond to
a sinoie stimulation with two or three successive
contractions.

" A point of specially physiological interest may
be here noticed. In its unmutilated state the fresh-
water Medusa exhibits the power of localizing with
its manubrium a seat of stimulation situated in the
bell; that is to say, when a part of the bell is
nipped with the forceps, or otherwise irritated, the
free end of the manubrium is moved over and
applied to the part irritated. So far the movement
of localization is precisely similar to that which I
have previously described as occurring in Tiaropsis
indicans {Phil. Trans., vol. clxvii.). But further
than this, I find a curious difference. For while
in Tiaropsis indicans these movements of localiza-
tion continue unimpaired after the margin of the
bell has been removed, and will be ineffectually
attempted even after the bell is almost entirely cut
away from its connections with the manubrium, in
the fresh-water Medusa these movements of localiza-

POISONS. 247

tion cease after the extreme margin of the bell has
been removed. For some reason or another the
integrity of the margin here seems to be necessary
forexciting the manubrium to perform its movements
of localization. It is clear that this reason must
either be that the margin contains the nerve-centres
which preside over these localizing movements of
the manubrium, or, much more probably, that it
contains some peripheral nervous structures which
are alone capable of transmitting to the manubrium
a stimulus adequate to evoke the movements of
localization. In its unmutilated state this Medusa
is at intervals perpetually applying the extremity
of its manubrium to one part or another of the
margin of the bell, the part of the margin touched
always bending in to meet the approaching ex-
tremity of the manubrium. In some cases it can
be seen that the object of this co-ordinated move-
ment is to allow the extremity of the manubrium —
i.e. the mouth of the animal — to pick off a small
particle of food that has become entangled in the
marginal tentacles. It is therefore not improbable
that in all cases this is the object of such move-
ments, although in most cases the particle which
is caught by the tentacles is too small to be seen
with the naked eye. As it is thus no doubt a
matter of great importance in the economy of the
Medusa that its marginal tentacles should be very
sensitive to contact with minute particles, so that a
very slight stimulus applied to them should start
the co-ordinated movements of localizati(<n, it is not
surprising that the tentacular rim should present

248 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

nerve-enrliiigs so far sensitive that only by tlieir
excitation can the reflex mechanism be thrown
into action. But if such is the expUmation in
this case, it is curious that in Tiaropsis indicans
eveiy part of the beli should be equally capable of
yielding a stimulus to a precisely similar reflex
action.

" In pursuance of this point, I tried the experi-
ment of cutting off ^portions of the margin, and
stimulating the bell above the portions of the mar-
gin which I had removed. I found that in this
case the manubrium did not remain passive as it
did when the ivhole margin of the bell was re-
moved ; but that it made ineflTectual efforts to find
the oflPending body, and in doing so always touched
some part of the margin which was still unmuti-
lated. I can only explain this fact by supposing
that tlie stimulus su})plied to the mutilated part is
spread over the bell, and falsely referred by the
manubrium to some part of the sensitive — i.e. un-
mutilated — margin.

"But to complete this account of the localizing
movements, it is necessary to state one additional
fact which, for the sake of clearness, I have hitherto
omitted. If any one of the four radial tubes is
irritated, the manubrium will correctly localize the
seat of irritation, whether or not the margin of the
bell has been previously removed. This greater
ease, so to speak, of localizing stimuli in the course
of the radial tubes than anywhere else in the
nectocalyx, except the margin, corresponds with
what I found to be the case in Tiaropsis indicans.

POISONS. 249

and probably has a direct reference to the distribu-
tion of the principal nerve-tracts.

" On the whole, therefore, contrasting this case of
localization with the closely parallel case i)resented by
Tiaropsis indicans, I sliould say that the two chiefly
ditfer in the fresh-water Medusa, even when unmuti-
lated, not being able to localize so promptly or so
certainly, and in the localization being only per-
formed with reference to the maroin and radial

o

tubes, instead of with reference to the whole ex-
citable surface of the animal.

"All marine Medusse are very intolerant of fresh
water, and, therefore, as the fresh- water species must
presumably have had marine ancestors,* it seemed
an interesting question to determine how far this
species would prove tolerant of sea- water. For the
sake of comparison, I shall first briefly describe
the effects of fresh water upon the marine species. f
If a naked-eved Medusa which is swimmincr
actively in sea-water is suddenly transferred to
fresh water, it will instantaneously collapse, become
motionless, and sink to the bottom of the containina
vessel. There it will remain motionless until it
dies ; but if it be again transferred to sea- water it
\7ill recover, provided that its exposure to the fresh
water has not been of too long duration. I have
never known a naked-eyed Medusa survive an ex-
posure of fifteen minutes; but they may survive

* Looking to the enormous number of marine species of
Medusa?, it is much more probable that the fi-esh-water species
was derived from them tlian that they were derived from a
fresh -water ancestry.

t For full account, see P^uL Trans., voL clxvii. pp. 744, 745.

250 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

an exposure of ten, and generally survive an ex-
posure of live. But altliough they thus continue
to live for an indetinite time, their vigour is con-
spicuously and permanently impaired ; while in
the fresh water irritability persists for a short time
after spontaneity has ceased, and the tentacles and
manubrium are strongly retracted.

" Turning now to the case of the fresh-water
species, when tirst it is dropped into sea-water at
85° there is no change in its movements for about
fifteen seconds, although the tentacles may be re-
tracted. But then, or a few seconds later, there
generally occurs a series of two or three tonic
spasms, separated from one another by an interval
of a few seconds. During the next half-minute the
ordinary contractions become progressively weaker,
until they fade aw^ay into mere twitching convul-
sions, which affect different parts of the bell irregu-
larly. After about a minute from the time of the
first immersion all movement ceases, the bell re-
maining passive in partial systole. There is now
no vestige of irritability. If transferred to fresh
water after five minutes' exposure, there immediately
supervenes a strong and persistent tonic spasm,
resembling rigor mortis, and the animal remains
motionless for about twenty minutes. Slight
twitching contractions then begin to display them-
selves, which, however, do not affect the whole bell,
but occur partially. The tonic spasm continues
progressively to increase in severity, and gives the
outline of the margin a very irregular form ; the
twitching contractions become weaker and less fre-

POISONS. 251

quent, till at last they altogether die away. Irrita-
bility, however, still continues for a time — a nip
with the forceps being followed by a bout of rhyth-
mical contractions. Death occurs in several hours
in strong and irregular systole.

" If the exposure to sea- water has only lasted two
minutes, a similar series of phenomena is presented,
except that the s})ontaneous twitching movements
supervene in much less time than twenty minutes.
But an exposure of one minute may determine a
fatal result a few hours after the Medusa has been
restored to fresh water.

"Contact with sea- water causes an opalescence
and eventual disintegration of the tissues, which
precisely resemble the effects of fresh water upon
the marine Medus^^. When immersed in sea-water
this Medusa floats upon the surface, owing to its
smaller specific gravity.

" In diluted sea-water (fifty per cent.) the pre-
liminary tonic spasms do not occur, but all the
other phases are the same, though extended through
a longer period. In sea- water still more diluted
(I in 4 or 6) there is a gradual loss of spontaneity,
till all movement ceases, shortly after which irri-
tability also disappears ; manubrium and tentacles
expanded. After an hour's continued exposure,
intense rigor mortis slowly and progressively de-
velopes itself, so that at last the bell lias shrivelled
almost to nothing. An exposure of a few minutes
to this strength [)laces the animal past recovery
when restored to fresh water. In still weaker mix-
tures (1 in 8, or 1 in 10) spontaneity persists for a

252 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

longtime; but the aniinal gradually becomes less
and less energetic, till at last it will only move in
a bout of feeble pulsations v.-hen irritated. In still
weaker solutions (1 in 12, or 1 in 15) spontaneity
continues for hours, and in solutions of from 1 in 15,
or 1 in IS, the Medusa will swim about for days.

" It will be seen from this account that the fresh-
water Medusa is even more intolerant of sea-water
than are the marine species of fresh water. More-
over, the fresh- water Medusa is beyond all comparison
more intolerant of sea-water than are the marine
species of brine ; for I have previously found
that the marine species will survive many hours'
immersion in a saturated solution of salt. While
in such a solution they are motionless, with manu-
brium and tentacles relaxed, so resembling the
fresh-water Medusa shortly after being immersed
in a mixture of one part sea- water to five of fresh ;
but there is the great difference that, while this
small amount of salt is very quickly fatal to the
fresh-water species, the large addition of salt exerts
no permanently deleterious influence on the marine
species.

" We have thus altogether a curious set of cross
relations. It would appear that a much less pro-
found ph3'siological change would be required to
transmute a sea-water jelly-fish into a jelly-fish
adapted to inhabit brine, than would be required to
enable it to inhabit fresh water. Yet the latter is
the direction in which the modification has taken
place, and taken place so completely that the sea-
water is now more poisonous to the modified species

POISONS. 253

than is fresh water to the nnmoclified. There can
be no doubt that the modification was p-radual —
probably brought about by the ancestors of the
fresh-water INIedusa penetrating higher and higher
through the brackish waters of estuaries into the
fresh water of rivers — and it would, I think, be
hard to point to a more remarkable case of pro-
found physiological modification in adaptation to
changed conditions of life. If an animal so exceed-
ingly intolerant of fresh water as is a marine jelly-
fish may yet have all its tissues changed so as to
adapt them to thrive in fresh water, and even die
after an exposure of one minute to their ancestral
element, assuredly we can see no reason why any
animal in earth or sea or anywdiere else may not in
time become fitted to change its element." *

* While these sheets are passing through the press, a paper
has been read before the Rojal Society by Mr. A. G. Bourne,
describing the hydroid stage of the fresh-Avater Medusa {Proc.
Roy. Soc, Dec. 11, 1884). lie has discovered the hydroids on the
roots of the Pontedcria, which have been growing in the Lily,
lack for several years, and which are therefore probably the
source from wliich the tank became impregnated with the
Medu8a3.

CHAFTER X.

STAR-FISH AND SEA-UIICHINS.

Structure of Star-fish and Sea- Urchins.

We shall now proceed to consider in tlie organization
of the Echinodermata a type of nervous system
which is more highly developed than that of the
Medusre. In conducting this research, I was joined
by my friend Professor J. Cossar Ewart, to whose
unusual skill and untiring patience the anatomical
part of the inquiry is due. But here, as formerly,
I shall devote myself to the physiology of the sub-
ject, as it is not possible within the limits assigned
to this volume to travel further into morphology
than is necessary for the purpose of rendering the
experiments intelligible. I shall therefore begin by
seeking to give merely such a general idea of the
structure of the Echinodermata as is necessary for
this purpose.

As we all know, a Star-fish consists of a central
disc and five radiating arms (Fig. 82 \ Upon the
whole of the upper surface there occur numerous
calcareous nodules embedded in the soft tiesh, and
supporting short spines. One of these nodules is
much larger than any of the others, is constant in

STAR- FISH AND SEA-URCHINS.

255

position, and is called the madre]:>oric tubercle
(Fig 32, 771). Continuing our examination of the
upper surface, we may observe, when we use a lens,
a number of small pincer-like organs scattered about
between the calcareous nodules, or attached to the
spines ; these are known as the pedicellariae. Each

Fig. 32. Upper surface of a Star-fish {Astropeckn).
Hist.")

(From Cassell's " Nat.

consists of a stalk serving to support a pair of
forceps or pincers, and the whole being provided
with muscles, the stalk is able to sway about and
the pincers to open and shut (Fig. 33). The entire
mechanism is therefore clearly adapted to seizing
and holding on to something ; but what it is that
these curious orcjans ai-e thus adapted to seize, and

256 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

therefore of what use they are in the economy of
the animal, has long been a standing puzzle to
naturalists. I hope presently to be able to show-
that we have succeeded in doing something towards
the solution of this puzzle.

Fig. 33.— redicellariae (magnified). (From Cassell's «• Nat. Hist.";

Turninir now to the under surface of our Star-fish
(Fig. 34), %^e observe that the mouth is situated in
the centre of the disc, and that from this mouth as
a centre there radiate five grooves or furrows, Avhich
severally extend to the tips of each of the five rays.
On each side of these grooves there are numerous
actively moving membraneous tubes, which may be
protruded or retracted by being filled or em[)tied
w^ith fluid. These are used for crawding, and I
shall therefore call them the feet, or pedicels.

So much, then, for the external surface of a Star-
fish. If, now, we examine the internal stincture, we

STAR-FISH AND SEA-UKCHINS.

257

find that the central mouth leads by a short oeso-
plia<njs into a central stomach, and that tliis in turn

i o '

communicates with the intestine, which terminates
in an orifice on the dorsal surface. Springing
from the intestine at its origin, there are five tubes,
each of wdiich divides into two, and the five pairs
of tubes thus formed extend into the five rays ;

Fig. 34.— Lower suifacp of common Star-fish.

numerous blind processes gi-ow out from these tubes,
and give rise to glandular structures, which pro-
bably perform the functions of a liver.

When a section is made across the base of one of
the arms, the furrows or grooves before mentioned
are seen to be formed of two rows of plates con-

258 JELLY-FISH, STAR-FISH, AND SEA-UKCHINS.

nccted together so as to compose a series of struc-
tures not unlike the couples of an ordinary roof.
These so-called ambulacral plates rest on liorizontal
spine bearing plates, from which other larger plates
extend u[)\vards to form the sides of the arms.

In a living Star-fish the tube-feet or pedicels
already mentioned are seen projecting from each
side of the ambulacral groove ; and, Avith the excep-
tion of a few at the tip of each arm, all the tube-

Fig. 35. — The terminal portion of a tube foot (in.Tgnified).

feet terminate in a well-formed sucker, by means of
which they can be firmly fixed to a flat surface
(Fig. 35).

If we wish to understand the structure and
mechanism of this locomotor or ambulacral system
— which, I may observe in passing, is of special
interest from the fact that as a mechanism it is
unique in the animal kingdom — w^e must resort to
dissection. We then find that each of the tube-feet

STAR-FISH AND SEA-URCHINS. 259

is provided in its membraneous walls with a number
of annular or ring-shaped muscular fibres ; when
these fibres contract, the fluid contained in the tube
is forced back, Avliile, conversely, when these fibres
relax, the fluid runs into the tube. If the contrac-
tion of these fibres is strong, the tube shrinks up
entirely, i.e. is retracted within the body of the
animal ; but if the contraction of the fibres is not
so strong, the tube is only shortened. If, before its
shortening, its terminal expansion, or sucker, has
been applied to any flat surface, the effect of the
shortening is to cause the sucker to adhere to the
flat surface, in consequence of the pressure of
the surrounding sea-water being greater than that
of the fluid within the shortened tube. In this
way, by alternately contracting and relaxing the
muscular fibres in the walls of a tube-foot, a Star-
fish is able alternately to cause the terminal sucker
to fasten upon and to leave go of any flat surface
upon which the animal may be crawling. In other
words, when the tube-foot is about to form its
attachment to a flat surface, it is fully distended
wdth fluid ; but when the terminal sucker touches
the flat surface, this fluid is partly withdrawn, so
causing the sucker to adhere.

When we dissect out one of these tube-feet, wo
find that at its base, within the body of the animal,
it bifurcates into two branches. One of these branches
passes immediately into a closed sac (Fig. 3C, /),
while the other passes into a large tube (Fig. 3G, k),
which runs all the way from base to tip of the ray,
receivinjx in its course similar branches from all the

260 JELLY-FISH, STAR-FISII, AND SEA-URCHINS.

tube-feet in the ray. This common or radial tube
itself opens into a circular tube (Fig, 30, e) sur-
rounding the mouth of the animal (Fig. 86 m). This
circular tube therefore receives five radial tubes —
one from each of the live rays — and is likewise in
communication with a number of membraneous sacs
(Fig. 36, c, d), resembling in their structure (though

Fig. 36. — Dagram of ambuldcral sv^lem of a Star-fish : a, madreporic canal; h,
inner end; g. outer end ot sums leadinc; to tircular neural vessel , h, from which
radial neural vessels, I, .irise ; c d, Folun vehicles ^/, ampulhc •, m, oval aperture;
n. madreporic plate.

larger in size) those which occur at the base of each
of the tube-feet. The function both of these sacs
and of those at the base of each tube-foot is the
same, namely, that of acting as reservoirs of the
fluid when this is expelled from the tube-feet.

STAR-FISH AND SEA-URCHINS. 2G1

Moreover, all these membraneous sacs are provided
with ring-shaped muscular fibres in their mem-
braneous walls, which therefore serve as antagonists
to the ring-shaped muscles which occur in the
membraneous Avails of the tube-feet ; that is to
say, when the muscles of the reservoirs contract
(Fig. 3G, c, d,f\ ), the pressure in the tube-feet is in-
creased, and when these muscles relax, that pressure
is diminished. The animal is thus furnished with
the means of varying the head of pressure in its
tube-feet, either locally or universally.

The circular tube surrounding the mouth com-
municates at one point with a calcareous tube
(Fig. 36, a), which runs straight to the dorsal surface
of the animal, and there terminates in the madre-
poric tubercle, to which I have already directed
attention (Fig. 82, m, and Fig. r3G, m). Thus it will
be seen that all the pedicels of all the rays are in
communication, by means of a closed system of
tubes, w^ith this madreporic tubercle. It has there-
fore been surmised that the function of this tubercle
is that of acting as a filter to the sea-water wdiich
in large part constitutes the fluid that fills the
ambulacral system. We have been able to prove
that this surmise is correct ; for we found that if
we injected any part of the ambulacral system with
coloured fluid — maintaining the injection for several
hours at as great a pressure as the tubes would
stand without rupturing — the coloured fluid found
its way up the calcareous tube to the ma Ireporic tu-
bercle, on arriving at which it slowly oozed through
the porous substance of whicli that tubercle consists.

18

262 JELLY-FISH, STAR-FISH, AND SEA URCHINS.

Such, tlien, is tlie so-called ambulacral system of
the Star-fish. Passing over anotlicr system of vessels
which I need not wait to describe (Fig. 06, g, h, I),
we come next to the nervous system. Tliis is dis-
posed on a very simple plan. It consists of a penta-
gonal ring surrounding the mouth, from which a
nerve-trunk passes into each of the five rays, to
run along the ambulacral groove as far as the ex-
treme tip of the ray, where it ends in a small red
pigmented spot, about which I shall have more to
say presently. Each of these five radial nerves
gives off in its course a number of delicate branches
to the tube-feet.

Modifications of the Starfish Type.

So much, then, for the structure of the common
Star-fish. I must next say a few words on the re-
markable modifications which this structure under-
goes in different members of the Star-fish group.

In some species tho size of the central disc is
increased so as to fill up the interspaces between
the rays, the whole animal being thus converted
into the form of a pentagon. In other species,
again, the reverse process has taken place, the rays
having become relatively longer, and being at the
same time very active; they look like five little
snakes joined together by a circular disc (Fig. 37).
Again, in another species the ra3\s have begun to
branch, these branches again to branch, and so on
till the whole animal looks like a mat. But the
mo.^t exticiue modifications are attained in the

STAn-FISH AND SEA-URCHINS.

263

sea cucumbers and lily-stars (Fig. 38). Without,
however, waiting to consider these, I shall go a
little more particularly into the modification of
Star-fish structure which is ]ircscntcd by the
sea-urchin, oi- Echinus ,Fig. 30).

Fig 37.— A Brit'le-star. (From CasseH's "Nat. Hist.")

Externally, the animal presents the form of an
orange, and is completely covered with a large
number of hard calcareous spines, on which account
it derives its scientific name of Echinus, or hedge-
hog (the spines have l»een removed from the larger
portion of the specimen represented in Fig. 31i). In
the living animal these spines are fully movable
in all directions, each beino- mounted on a ball-and-

264 JELLV-FISH, STAR-FISH, AND SEA-URCHINS.

socket joint, and provided with muscles at its base.
On the external surface, besides the spines, we

Pfg. 38.— A Lily-star. (From CasseU's "Nat. Hist.")

meet with pedicellari?e (Fig. 33 magnified), and also
with the madreporic tubercle (Fig. 39, m). The
pedicellariaj in their niain features resemble those

STAR-FISH AND SEA-URCIUNS.

265

which occur in the Star-fish, though considerably
larger, and the ambulacial system is constructed

Fig. 39.— A.n Echinus, partly denuded of its spines. (From Cassell's "Nat.
Hist.")

upon the same plan. If we shave off the spines
and pedicellari'ce (Fig. 39), w^e find that we come to

Fig. 40.— Showing iiit> lior ul Echinus shell. (From Cassell's " Nat. Hist.")

a hard shell, which, if we break, we find to be
hollow^ and filled with fluid (Fig. 40\ The fluid

2G6 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

closely resembles sea-water, but is, nevertheless,
richly corpusculated ; it coagulates when exposed
to the air, and otherwise shows that it is something
more than mere sea- water. If we look closely into
the shell which has been deprived of its spines, we
find that it is composed of a great number of small
hexagonal j)lates (Fig. 41), the edges of which fit £0
closely together that the whole shell is converted
into a box, Avhich, when the animal is alive, is
water-tight, as we have proved by submitting the
contained fluid to hydrostatic pressure, under which

»-j3LV >

n .1 /

O 0 J

r" mQl

Fig. 41.— A portion of the external shell of an Echinus denuned of ppines and
slightly magnified, showing the arrangement of the plates, the balls in the ball-
and-socket joints of the spines, and the holes through which the ambulacral feet
are protruded. (From Cas.-ell's "Nat. Hist.")

circumstances there is no leakage until the pressui-e
is sufficient to burst the shell Nevertheless, if we
look closely at the dned shell of an Echinus, we
shall .see that it is not an absolutely closed box ; for
we shall see that the hexagonal plates are so arranged
as to give rise to five double rows of holes or pores
(Fig. 41), which extend symmetrically from pole to
pole of the animal (Fig. 39). It is through these
holes that the tube-feet are protruded ; so that if
we imagine a pentagonal species of Star-fish to be
curved into the shape of a hollow spheroid, and
then converted into a calcareous box with holes

STAR-FISH AND SEA-UKCHINS. 2C7

left for its feet to come through, we should have a
mental picture of an Echinus. It would only be
necessary to add the curious apparatus of teeth
(Figs. 40 and 42), which occurs in the Echinus, to
increase the size of tlie spines and pedicellariae, and
to make a few other such minor alterations ; but in
all its main features an Echinus is merely a Star-
fish with its five rays calcified and soldered together
so as to constitute a riicid box.

This echinoid type itself varies considerably
among its numerous constituent species as to size,
shape, length and thickness of the spines, etc. ; but

Fig. -12.— Teeth of Kcliiiiu^- (Irom CisseU's " Nat. Hist.")

I need not wait to go into these details. Again,
merely inviting momentary attention to the develop-
mental history of these animals, I may remark that
the phases of development through which an indi-
vidual Echinoderm passes are not less varied and
remarkable than are the permanent forms eventually
assumed by the sundry species.

Katura I Movem en fs.

Turning now to the physiology of the Star-fish
group, I shall begin by describing the natural
movements of the animals.

26S JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

Takinor the common Star-fish as our stavtingr-
point, I have ahxady explained the mechanism
of its ambulacral system. The animals usually
crawl in a determinate direction, and when in the
course of their advance the terminal feet of the
advancing ray — which are used, not as suckers, but
as feelers, protruded forwards — happen to come into
contact with a solid bod}^ the Star-fish may either
continue its direction of advance unchanged, or
may turn towards the body which it has touched.
Thus, for instance, while crawling along the floor ot
a tank, if the terminal feet at the end of a ray
happen to touch a perpendicular side of the tank,
the animal may either at once proceed to ascend
this perpendicular side, or it may continue its
progress along the floor, feeling the perpendicular
side with the end of its rays perhaps the whole way
round the tank, and yet not choosing, as it were, to
ascend. In the cases where it does ascend and
reaches the surface of the water, a Star-fish very
often performs a number of peculiar movements,
which we may call acrobatic (Fig. 43). On reaching
the surface, the animal does not wish to leave its
native element — in fact, cannot do so, because its
sucking feet can only act under water — and neither
does it wish again to descend into the levels from
which it has just ascendcJ. It, therefore, begins to
feel about for rocks or sea-weeds at the surface, by
crawlinof alon^' the side of the tank, and every now
and then throwing back its uppermost ray or rays
along the surface of the water to feel for any solid
support that may be within reach. If it finds one,

STAR-FISH AND SEA-URCHINS.

269

it may very likely attach its uppermost rays to it,
and then, letting go its other attachments, swing
from the one support to the other. The activity
and co-ordination manifested in these acrobatic
movements are surprising, and give to the animal
an almost intelligent appearance.

In Astropecten the ambulacral feet have become
partly rudnnentary, inasmuch as they have lost

Fig. 43.— Natural movements of a Star-fieh on reaching the surface of water.

their terminal suckers (Fig. 44). These Star-fish,
therefore, assist themselves in locomotion by the
muscular movements of their rpys, while they use
their suckeiiess feet to run along the ground some-
what after the manner of centipedes. It is to be
noticed, however, that altliough the feet have lost
their suckers, the Star-hsh is still able to make them
adhere io solid surfaces in a comparatively inefficient

270 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

manner, by constricting the tube on one side after
it has brought this side into opposition with the
solid surface (Fig. 45).

In the Brittle-stars the ambulacra! feet have been
still more reduced to rudiments, and are of no use
at all, cither as suckers or for assisting in locomotion.
These Star-fish have, therefore, adopted another
method of locomotion, and one which is a great

Fig. 44. — .\ pedicel of Astropecten
(magnified), showing the absence
of any terminal sucker.

Fig. 45.— The same, showing the
method of extemporizing a
sucker.

improvement upon the slow crawling of other
members of the Star-fish group. The rays of the
Brittle-stars are very long, flexible, and muscular,
and by their combined action the animal is able
to shuffle along fiat horizontal surfaces. When it
desires to move rapidly, it uses two of its opposite
arms upon the horizontal floor with a motion like
46) ; at each stroke the animal

swimming (Fi

STAR-FISH AND SEA-UPtCIIIXS. 271

adv^anccs with a leap or bound about the distance
of two inches, and as the strokes follow one another
rapidly, the Star-lish is able to travel at the rate of
six feet per minute. A common Star-lish, on the
other hand, with its slow crawling method of

Fig. 46.— Natunil movements of a Brittle-star when proceeding along a solid
horizontal surface.

progression, can only go two inches per minute.
Some of the Comatuhe, in which the muscularity
of the rays has proceeded still further, are able
actually to swim in the water by the co-ordinated
movements of their rays.*

* In this cas9 the locomotion of a Star-fish comes to be per-
formed on the same plan or method as that of a Jelly-fish — the
five rays performing, by their co-ordinated action, the same
function as a swimming-bell. It is a cnrionsly interesting fact,
that although no two plans or mechanisms of locomotion could
well bo imagined as more fundamentally distinct than those
which are respectively characteristic of these two groups of

272 JELLY-FISH, STARFISH, AND SEA-URCHINS.

The Ecliiniis crawls in the same way as the
common Star-fish; but besides its long suckers it
also uses its spines, wdiich by their co-ordinated
action push tlie animal along. The suckers, more-
over, in being protruded from all sides of a globe
instead of from the under side of a flat oi'ganism,
are of much more use as feelers than they are in the
Star-fish. Therefore, wdiile advancing, the feet
facing the direction of advance are always kept
extended to their fullest length, in order to feel for
any object which the animal may possibly be
approaching. When a perpendicular surface is
reached, the Echinus may either ascend it or not, as
in the case of the Star-fish. While walking, the
animal keeps pretty persistently in one direction
of advance. If it be partly rotated by the hand,
it does not continue in the same direction, but
continues its own movements as before ; so that,
for instance, if it is turned half round, it will
proceed in a direction opposite to that in which
it had previously been going. When at rest, some
of the feet are used as anchors, and others protruded
as feelers.

Regarded from the standpoint of the evolutionist,
we have here an interesting series of gradations.
At one end of the series we have the Echinus with
its rays all united in a box-like rigid shell. At
the other end of the series we have the Brittle-stars
and Comatuhie with their highly muscular and

animals, nevertheless in this particular case and in virtue
of special modilication, a Star-fish should have adopted the plan
or mechanism of a Jelly-fish.

STAR-FISH AND SEA-UllCIIINS. 2/3

mobile rays. J\[icl\vay in tlie series we have Astro-
pecten and the common Star-fish, where the rays
are flexible and mobile, though not nearly so much
so as in tlie Brittle-stars. Now, the point to observe
is, that in correlation with this graduated difference
in the mobility of the rays, there is a correspond-
ingly graduated difference in the development of
the ambulacral system of suckers. For in Echinus
this system is seen in its most elaborate and efficient
form ; in the common Star-fish the suckers are still
the most important organs of locomotion, though
the muscularity of the rays has begun to tell upon the
development of the specially ambulacral system,
the suckers not being so long or so powerful as
they are in Echinus. Lastly, the Brittle-stars and
ComatuhB have altogether discarded the use of
their sucking feet in favour of the much more
efficient organs of locomotion supplied by their
muscular rays ; and, as a consequence, their feet
have dwindled into useless rudiments, while the
rays have become limb-like in their activity.

There is only one other point in connection with
the natural movements of the Echinodermata which
it is necessary for me to touch upon. All the
species when turned upon their backs are able again
to right themselves ; but seeing, as I have just
observed, that tlie or!:»'ans of locomotion in the
different species are not the same, the methods to
which these species have to resort in executing the
righting manoeuvre are correspondingly diveise.
Thus, the Brittle-stars can easily perfoJ'm the need-
ful manoeuvre by wriggling some of their snake-

274 .IFXLY-FISH, STAR-FISH, AND SEA-URCHINS.

like arms under the inverted disc, and heaving the
whole bod}^ over by the mere muscularit}^ of these
organs. The common Star-fish, however, experiences
more difficult}', and executes the manoeuvre mainly
by means of its suckers. That is to say, it twists
round the tip of one or more of its rays (Fig. 47)
until the ambulacral feet there situated are able to

Fig. 47. — Natural righting rmvements of ronimon Star-fish.

get a firm hold of the floor of the tank (a) ; then, by
a successive and similar action of the ambulacral
feet further back in the series, the whole ray is
twisted round (b), so that the ambulacral surface
cf the end is applied flat against the floor of the
tank (c). The manoeuvre continuing, the semi-turn

STAR-FISH AND SEA-URCHINS. 275

or spiral travels ])rogressing all the way down the
ra}'. Usually two or three adjacent rays perform
this mantieuvre simultaneously ; but if, as some-
times ha])pens, two opposite rays should begin to
do so, one of them soon ceases to continue the
manoeuvre, and one or both of the ra3^s adjacent to
the other takes it up instead, so assisting and
not thwarting the action. The spirals of the co-
operating rays being invariably turned in the same
direction (Fig. 47, a, b, and c), the result is, when
they have proceeded sufficiently far down the rays,
to drag over the remaining rays, which then
abandon their hold of the bottom of the tank, so as
not to offer any resistance to the lifting action oi
the active rays. The whole movement does not
occupy moie than half a minute. As a general
rule, the rays are from the first co-ordinated to
effect the rIo*htin2f movement in the direction in
which it is finally to take place — the ra3^s which
are to be the active ones alone twistinof over, and
so twisting that all their spirals turn in the same
direction.

A Star-fish (Astropecten) which is intermediate
between the Brittle-star and the common Star-fish, in
that its ambulacral feet are partly aborted (having
lost their suckers, as shown in Fig. 44) and its
rays more mobile than those of the common Star-
fish, rio'hts itself after the manner shown in Fi^;. 48,
where the animal is represented as standing on the
tips of four of its rays, while the fifth one is just
about to bo thrown upwards and over the others, in
order to cai ry with it the two adjacent rays, and so

276 JELLY-FISH, STAR-FISH, AND SEA-URCHmS.

eventually to overbalance the system round the
fulcrum supplied by the tips of the other two rays,
and thus bring the animal down upon its ventral
surface.

But it is in the case of Echinus that these right-
ing movements become most interesting, from the
fact that they are so much more difficult to accom-

Fig 48. — Righting movements of Astr.'pecten.

plish than they are in the case of the Star-fishes.
For while a Star-tish is provided with flat, flexible,
and muscular rays, comprising a small and light
mass in relation to the motive power, an Echinus
is a rigid, non-muscular, and globular mass, whose
only motive power available for conducting the
mancEuvre is that which is supplied by its re-

STAR-FISH AND SEA-URCHIXS. 277

latively feeble ambulacral feet. It is, therefore,
scarcely surprisino- that unless the specimens chosen
for these observations are perfectly fresh and
vigorous, they are unable to riglit themselves at
all ; they remain permanently inverted till they
die. But if the specimens are fresh and vigorous,
they are sooner or later sure to succeed in right-
ing themselves, and their method of doing so is
always the same. Two, or perhaps three, adjacent
rows of suckers are chosen out of the five, as the
rows which are to accomplish the task (Fig. 49). As

iilll|lNII|lllil||![iiIplll|l||l|l|||||||iiill!ll|ilil!il|||l|i|illllllllllll|ll|i|lll|!|l|llll|l|||K^^^
Fig. 49.

many feet upon the rows as can reach the floor of

the tank are protruded downwards and fastened

firmly to the floor; their combined action then

serves to tilt the globe slightly over in their own

direction, the anchoring feet on the other or

opposite rows meanwhile releasing their hold of the

tank to admit of this tilting (Fig. 50). The effect

of this tilting is to enable the next feet in the

active ambulacral rows to touch the floor of the

tank, and, when they have established their hold,
19

2/8 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

tliev assist in increasing^ the tilt ; then the next feet
in the series lay hold, and so on, till the globe

Fig. 50.

slowly but steadily rises upon its equator (Fig. 51).
The difficulty of raising such a heavy mass into

Fig. 51.

this position by means of the slender motive power

STAR-FISH AND SEAUrtCHINS. 279

available can be at once appreciated on witnessing
the performance, so that one is surprised, notwith-
standing the co-ordination displayed by all the
suckers, that they are able to accomplish the work
assigned to them. That the process is in truth a
very laborious one is manifest, not only from the
extreme slowness with which it takes place, but
also because, as already observed, in the case of not
perfectly strong specimens complete failure may
attend the efforts to reach the position of resting on
the equator — the Echinus, after rearing up a certain
height, becoming exhausted and again falling back
upon its ab-oral pole. I\roreover, in some cases it
is interesting to observe that when the equator
position has been reached with difficulty, the
Echinus, as it were, gives itself a breathing space
before beginning the movement of descent — drawing
in all its pedicels save those which hold it securely
in the position to which it has attained, and
remaining in a state of absolute quiescence for a
prolonged time. It then suddenly begins to protrude
all its feet again, and to continue its manoeuvre.
At any time during such a period of rest, a stimulus
of any kind will immediately determine a recom-
mencement of the manoeuvre.

It will be perceived that as soon as the position
just described has been attained, gravity, which had
hitherto been acting in opposition to the righting
movement, now begins to favour that movement.
It might, therefore, be anticipated that the Echinus
would now simply let go all its attachments and
allow itself to roll over into its natural position

280 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

But an Echinus will never let go its attachments
without some uro^ent reason, seemingr to be above
all things afraid of being rolled about at the mercy
of currents ; and therefore in this case it lets itself
down almost as slowly as it raised itself up. So
gently, indeed, is the downward movement effected,
that an observer can scarcely tell the precise
moment at which the ricrhtins: is concluded. There-
fore, in the downward movement, the feet, which at
the earlier part of the manoeuvre were employed

lililllilillllllllllllli!llyiiniiii!,i'!'!!"i!!ill!!'l!'iiO

Fig. 52.

successfully in rearing the globe upon its equator,
are now employed successfully in preventing its too
rapid descent (Fig. 52).

Several interesting questions arise with reference
to these righting movements of Echinus. First of
all we are inclined to ask what it is that determines
the choice of the rows of feet which are delegated
to effect the movements. As the animal has a
geometrical form of perfect symmetry, we might
suppose that when it is placed upon its pole, all the

STAR-FISH AND SEA-URCHIXS. 281

five rows of feet would act in antag-onism to one
another; for there seems nothinix more to determine
either the action or the inaction of one row rather
than another. Indeed, if there were any moral
philosophers among the Echinoderms, they might
point with triumph to the fact of their being able
to right themselves as an irrefutable argument in
favour of the freedom of the Echinoderm will. " We
are in form," they might say, " perfectly geometrical,
and our feet-rows are all arranged with perfect
symmetry ; therefore there is no reason, apart from
the sovereign freedom of our choice, why we should
ever use one set of feet rather than another in exe-
cuting this important movement." And indeed, I
do not see how these Echinoderm philosophers could
be answered by any of the human philosophers, who,
with less mathematical data and with less physio-
logical reason, employ analogous arguments to prove
the freedom of the human will. Physiologists,
however, would give these Echinoderm philosophers
the same answer that they are in the habit of giving
to the human philosophers, viz. that although the
physiological conditions are very nicely balanced,
they are never so nicely balanced as to leave
positively nothing to determine which rows of feet
— that is to say, which sets of nerves — shall be
used. And in this connection I may observe that
on making a number of trials it becomes apparent
in the case of certain individual specimens that
they manifested a marked tendency to rotate
always in the same direction, or to use the same set
of foot-rows for the purpose of righting themselves.

282 JELLY-FISH, STAR-FISH, AND SEA-UUCIIINS.

In tliese individual specimens, therefore, we must
conclude tliat the foot-rows thus employed are
selected because of some slight accidental prepotency
or superiority over the others ; the animal has, as it
wore, thus much individual character as the result
of a slight prepotency of some of its nerve-centres
over the others.

Another question of still more interest arises out
of these righting movements, namely, that as to
their prompting cause. This question, however, I
shall defer till later on, since it cannot be answered
without the aid of experiments as distinguished
from observation.

Stmiulation.

In now quitting our observations on the natural
movements of the Echiiiodermata, and beo-innino^ an
account of the various experiments which we have
tried upon these animals, I shall first take the
experiments in stimulation.

All the Echinodermata seek to escape from
injury. Thus, for instance, if a Star-fish or an
Echinus is advancing continuously in one direc-
tion, and if it be pricked or otherwise irritated
on any part of an excitable surface facing the
direction of advance, the animal immediately
reverses that direction. There is one point of
special interest concerning these movements of
response to stimulation. The form of the animals
and the distribution of the nervous system being,
as I have before said, of geometrical regularity, it
follows that by applying two stimuli simultaneously

STAR-FISH AND SEA-URCHINS. 283

on two (lifrerent aspects of the animal, the combined
result uf these two stimuli is that of furnishing a
very pretty instance in physiology of the physical
principle of the parallelogram of forces. Thus, for
instance, if two stimuli of equal intensity be applied
simultaneously at the opposite sides of a globular
Echinus, the animal begins to walk in a direction
at right angles to an imaginary line joining these
two points. And, generally, wherever the two
points of simultaneous stimulation may be situated,
the direction of the animal's advance is the
diagonal between them. As showino- in more detail
how very delicate is the physiological balancing of
stimuli which may be produced in these organisms,
and consequently the manner in which we are able
to play, as it were, upon their geometrically
disposed nervous systems in illustration of the
mechanical principle of the composition of forces,
I shall quote a series of observations.

" 1. Scraped with a scalpel the equator of an
Echinus at two points opposite to each other —
animal crawled at right angles to the line of injury.

"2. Similarly scraped at the ab-oral pole — no
effect. There was no reason why injury here should
determine escape in one direction rather than in
another.

" 3. Scraped similarly near the oral pole, and
half-way between pole and equator — little or no
effect.

"4. Scraped in rapid succession five equatorial and
equidistant injuries — Echinus crawled actively in
one determinate direction; the equal and equi-

284 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

distant injuries all round the globe neutralized one
another.

** 5. Scraped a band of uniform width all the way
round the equator — same result as in 4.

"6. Band of injury in same specimen was then
widened in the side facing' the direction of crawlino^
— no effect. Still further widened — slii^ht chans^e
of direction, and, after a time, persistent cravvding
away from the widest part of the injured zone.
Repeated this experiment on other specimens by
scraping round the whole equator, and simultane-
ously making one part of the zone of injury wider
than the rest — same result; the animal crawled
away from the greatest aQnount of injury.

" 7. Scraped on one side of the equator, and, after
the animal had been cravv^ling in a direct line from
the source of irritation for a few minutes, similarly
scraped equator on the opposite side — animal re-
versed its direction of crawling ; it crawled away
from the stimulus supplied latest.

"8. Scraped a number of places on all aspects
of the animal indiscriminately — direction of ad-
vance uncertain and discontinuous, with a strons:
tendency to rotation upon vertical axis."

These observations show conclusively that the
whole external surface, not only of the soft and
fleshy Star-fish, but even of the hard and rigid
Echinus, is everj^where sensitive to stimulation.
Closer observation shows that this sensitiveness,
besides being so general, is highly delicate. For if
any part of the external surface of an Echinus is
lightly touched with the point of a needle, all the feet,

STAR-FISH AND SEA-URCHINS. 285

spines, and pedlcellari?e within reach of that part, and
even beyond it, immediately converge and close in
u[)on the needle, grasp it, and hold it fast. This simul-
taneous movement of sucli a little forest of prehensile
organs is a very beautiful spectacle to witness. In
executing it the pedicellarici3 are the most active,
the spines somewhat slower, and the feet very
much slower. The area affected is usually about
half a square inch, although the pedicellarise even
far beyond this area may bend over towards the
seat of stimulation, which, however, from their small
size they are not able to reach.

And here we have proof of the function of the
pedicellariie — proof which w^e consider to be im-
portant, because, as I have before said, the use of
these organs has so long been a puzzle to naturalists.
In climbing perpendicular or inclined surfaces of
rock, covered with waving sea-weeds, it must be of
no small advantage to an Echinus to be provided on
all sides with a multitude of forceps, all mounted
on movable stalks, which instantaneously bring
their grasping forceps to bear upon and to seize a
passing frond. The frond being thus arrested, the
spines come to the assistance of the pedicell arise,
and both together hold the Echinus to the support
furnished by the sea-weed. Moreover the sea-weed
is thus held steady till the ambulacral feet have
time also to establish their hold upon it w^th their
sucking discs. That the grasping and arresting of
fronds of sea- weed in this way for the purposes of
xocomotion constitute an important function of the
pedicellarige, may at once be rendered evident

286 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

experimentally b}^ drawing a piece of sea-weed over
the surface of a healthy Echinus in the water. The
moment the sea-weed touches the surface of the
animal, it is seen and felt to be seized by a number
of these little grasping organs, and — unless torn
away by a greater force than is likely to occur in
currents below the surface of the sea — it is held
steady till the ambulacral suckers have time to
establish their attachments upon it. Thus there is
no doubt that the pedicellarise are able efficiently
to perform the function which we regard as
their chief function. We so regard this function,
not merely because it is the one that we observe
these organs chiefly to perform, but also because
we find that their whole physiology is adapted
to its performance. Thus their multitudinous
number and ubiquitous situation all over the
external surface of the animal is suggestive of
their being adapted to catch something which may
come upon them from any side, and which may
have strings and edges so fine as to admit of being
enclosed by the forceps. Again, the instantaneous
activity with which they all close round and seize
a moving body of a size that admits of their seizing
it, is suggestive of the objects which they are
adapted to seize being objects which rapidly brush
over the surface of the shell, and therefore objects
which, if they are to be seized at all, must be ionized
instantaneously. Lastly, we find, on experiment-
ing upon pedicellaria^, whether in sitit or when
separated from the Echinus, that the clasping action
of the forccp.^ is precisely adapted to the function

STAR-FISH AND SEA-URCHINS. 287

which we are considering ; for not only is the force
exerted by the forceps during their contraction of
an astonishing amount for the size of the organ
(the serrated mandibles of the trident pedicelJaiia?
holding on with a tenacity that can only have
reference to some objects liable to be dragged away
from their grasp), but it is very suggestive that this
wonderfully tenacious hold is spontaneously relaxed
after a minute or two. This is to say, the pedi-
cellaripe tightly fix the object which they have
caught for a time sufficient to enable the ambulacral
suckers to establish their connections with it, and
then they spontaneously leave go ; their grasp is not
only so exceedingly powerful while it lasts, but it is
as a rule timed to suit the requirements of the
pedicels.*

Concerning the physiology of the pedicellariie
little further remains to be said. It may be stated,
however, that the mandibles, which are constantly

* A further proof that this is at least one of the functions of
the pedicellariae is furnished by a simple experiment. If an
Echinus is allowed to attach its feet to a glass plate held just
above its ab-oral pole, and this plate be then raised in the water
so that the Echinus is freelj suspended in the water by means of
its feet alone, the animal feels, as it were, that its anchorage
is insecure, and actively moves about its unattached feet
to seek for other solid surfaces. Under such circumstance?
it may be observed that the pedicellariae also become active, and
especially so near the surface of attachment, as if seeking for
pieces of sea-weed. If a piece is presented to them, they lay
hold upon it with vigour.

Of course the pedicellariae may also have other functions to
perform, and ia a Star-fish Mr. Sladen has seen them engaged in
cleaning the surface of the animal ,• but we cannot doubt that at
least in Echinus their main function is that which we have stated.

283 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

swaying about upon their contractile stalks as if
in search for something to catch, will snap at an
object only if it touches the inner surface of one
or more of the expanded mandibles. Moreover, in
the larger pediccllariiie, a certain part of the inner
surface of the mandibles is much more sensitive to
contact than is the rest of that surface; this part is
a little pad about one-third of the way down the
mandible : a delicate touch w^ith a hair upon this
part of any of the three mandibles is certain to
determine an immediate closure of all the three. It
is obvious that there is an advantage in the sen-
sitive area, or zone, being placed thus low enough
down in the length of the mandibles to ensui-e that
the whole apparatus will not close upon an object
till the latter is far enough within the grasp of the
mechanism to give this mechanism the best possible
hold. If, for instance, the tips of the mandibles
were the most sensitive parts, or even if their whole
inner surfaces were uniformly sensitive, the ap-
paratus would be constantly closing upon objects
when these merely brushed past their tips, and
therefore closing prematurely for the purpose of
grasping. But, as it is, the appaiatus is admirably
adapted to waiting for the best possible chance of
getting a secure hold, and then snapping upon the
object witli all the quickness and tenacity of a
spring- trap.

Another point w^orth mentioning is that if, after
closure, any one or more of the mandibles be gently
stroked on its outer surface near the base, all the
mandibles are by this stimulation usually, though

STAR-FISH AND SEA-UnCIIfNS. 289

not invariably, induced again to expand. This is
the only pait of the whole organ the stimulation of
which thus exerts an inhibitory influence on the
contractile mechanism. If there is any functional
purpose served by such relaxing influence of stimu-
lating this particular part of the apparatus, we
think it can only be as follows. When a portion of
sea-weed brushes this particular part, it must be
well below the tips of the mandibles, and therefore
in a position where it, or some over-lying portion,
may soon pass between the mandibles, if the latter
are open; hence when touched in this place the
mandibles, if closed, open to receive the sea-weed,
should any part of it come within their cavity.

Turning next to experiments in stimulation with
reference to the spines, I may observe that we have
found these organs to be, physiologically considered,
highly remarkable and interesting, from the fact
that they display co-ordinated action in a degree
which entitles them to be regarded as a vast multi-
tude of limbs. Thus, for instance, if an Echinus be
taken out of the water and placed upon a table, it
is no longer able to use its feet for the purpose of
locomotion, as their suckers are only adapted to be
used under water. Yet the animal is able to pro-
gress slowly by means of the co-ordinated action of
its spines, which are used to prop and push the
globe-like shell along in some continuous direction.
If, while the animal is thus slowly progressing, a
liojhted match be held near it, facinor the direction of
advance, as soon as the animal comes close enough
to feel tho heat, all the spines begin to make the

290 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

animal move away in the opposite direction. More-
over, as showing the high degree in which the action
of the spines is co-orJihated, I may mention that
there is an urchin-like form of Echinoderra, which is
called Spatangus, and wdiich differs fi om the Echinus
in having shorter feet and longer spines. When,
therefore, a Spatangus is inverted, it is unable to
right itself by means of its feet, as these are too short
to admit of being used for this purpose ; but, never-
theless, the animal is able to right itself by means
of the co-ordinated action of its long spines, these
being used successively and laboriously to prop
and push the animal over in some one definite
direction. The process takes a very Jong time
to accomplish, and there are generally numerous
failures, but the creature perseveres until it eventu-
ally succeeds.

Coming now to stimulation with reference to the
feet, we find that when a drop of acid, or other
severe stimulation, is applied to any part of a row
of protruded pedicels, the entire row is immediately
retracted, the pedicels retracting successively from
the seat of irritation— so that if the latter be in the
middle point of the series, two series of retractions
are started, proceeding in opposite directions simul-
taneously ; the rate at which they travel is rather
slow. This process of retraction, however, although
so complete within the ray irritated, does not extend
to the other rays. But if the stimulus be applied
to the centre of the disc, upon the oral surface of
the animal, all the feet in all the rays are more or
less retracted— the process of retraction radiating

stah-fish and sea-urchins. 291

serially fi-om the centre of stimulation. The influ-
ence of the stimulus, however, diminishes perceptibly
with the distance from the centre. Thus, if weak
acid be used as the irritant, it is only the feet near
the bases of the rays that are retracted ; and even
if very strong acid be so used, it is only the feet as
far as one-half or two-thirds of the way up the rays
that are fully retracted — the remainder only having
their activity impaired, wdiile those near the tip may
not be adected at all. If the drop of acid be placed
on the dorsal, instead of the ventral surface of the
disc, the effect on the feet is found to be just the
converse ; that is, the stimulus here applied greatly
increases the activity of the feet. Further experi-
ments show that this effect is produced by a stimu-
lus applied anywhere over the dorsal aspect of the
animal ; so that, for instance, if a drop of acid be
placed on the skin at the edge of a ray, and there-
fore just external to the row of ambulacral feet, the
latter will be stimulated into increased activity ;
whereas, if the drop of acid had been placed a very
small distance past the edge of the ray, so as to
touch some of the feet themselves, then the whole
row would have been drawn in. We have here
rather an interesting case of antagonism, which is
particularly well marked in Astropecten, on account
of the active writhing movements which the feet
exhibit when stimulated by an irritant placed on
the dorsal surface of the animal. It may be added
that in this antagonism the inhibitory function is
the stronger ; for when the feet are in active motion,
owin^i' to an irritant actino- on the dorsal surface.

292 JELLY-FISH, STAR-FISH, AXD SEA-URCHINS.

they may be reduced to immediate quiescence — i.e.
retracted — by placing another irritant on the ven-
tral surface of the disc. Similarly, if retraction has
been produced by placing the irritant on the ventral
surface of the disc, activity cannot be again induced
by placing another drop of the irritant on the dorsal
surface.

Now, if we regard all these facts of stimulation
taken together, it becomes evident that the external
organs of an Echinoderm — feet, spines, and pedicel-
lari?e — are all highly co-ordinated in their action ;
and therefore the probability arises that they are
all held in communication with one another by
means of an external nervous plexus. Accordingly
we set to work on the external surface of the
Echinus to see whether we could obtain any evi-
dence of such a plexus microscopically. This we
succeeded in doing, and afterwards found that Pro-
fessor Loven had already brietly mentioned such
a plexus as having been observed by him. The
plexus consists of cells and fibres, closely distri-
buted all over the surface of the shell, immediately
under the epidermal layer of cells (Figs. 53, 54, 5o),
and it sends fibres all the way up the feet, spines,
and pedicellarise. As it seemed to us important
to investigate the physiological properties of this
plexus. Professor Ewart and I made a number of
further experiments, an account of which will now
lead us on to the next division of our subject, or
that of section.

STAR-FISH AND SEA-URCHINS.

293

rig. 53. Exiciiiul neivj-plexusof Edifiius.

Fig. 54. Structure of a nerve-trunk of Eclnnus.

r^>-~.^

Fig. 55. Nerve-cells lying among the muscnlir fibres at the base of a spine in
Echiuus.
20 "

294« JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

Sidlon,

1. Slar-iish. — Single rays cletacliecl from the
organism crawl as fast and in as determinate a
direction as do the entire animals. They also
crawl up perpendicular surfaces, and sometimes
away from injuries ; but the}^ do not invariably, or
even generally, seek to escape from the latter, as is
so certain to be the case with entire animals.
Lastly, when inverted, separated rays right them-
selves as quickly as do the unmutilated organisms.

Dividing the nerve in any part of its length has
the effect, whether or not the ray is detached from
the animal, of completely destroying all physio-
logical continuity between the pedicels on either
side of the line of division. Thus, for instance, if
the nerve be cut across half-way up its length, the
row of pedicels is at once physiologically bisected,
one-half of the row becoming as independent of the
other half as it would were the whole ray divided
into two parts : that is to say, the distal half of the
row may crawl while the proximal half is retracted,
or vice versa; and if a drop of acid be placed on
either half, the serial contraction of the pedicels
in that half stops abruptly at the line of nerve-
division. As a result of tliis complete physiological
severance, when a detached ray so mutilated is
inverted, it experiences much greater difficulty in
righting itself than it does before the nerve is
divided. The line of nerve-injury lies flat upon
the floor of the tank, Avhile the central and distal
portions of the ray, i.e. the portions on either side

STAR-FISH AND SEA-URCHINS. 295

of that line, assume various movements and
shapes. The central portion is particularly apt to
take on the form of an arch, in which the central
end of the severed ray and the line of nerve-section
constitute the points of support (tetanus ?) (Fig. oQ),
or the central end may from the first show paralysis,
from which it never recovers. The distal end, on
the other hand, usually continues active, twisting
about in various directions, and eventually fasten-
ing its tip upon the floor of the tank to begin the
spiral movement of righting itself This movement

Fi g. 56. Movements performed by a detached ray of a Star-fish, in which the
central nerve-trunk is divided.

then continues as far as the line of nerve-injury,
where it invariably stops (Fig. oQ). The central
portion may then be dragged over into the normal
position, or may remain permanently inverted,
according to the strength of pull exerted by the
distal portion ; as a rule, it does not itself assist in
the righting movement, although its feet usually
continue protruded and mobile. Thus, the effect of
a transverse section of the nerve in a ray is that
of completely destroying physiological continuity
between the pedicels on either side of the section.

296 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

The only other experiments in nerve-section to
which the simple anatomy of a Star- fish exposes
itself is that of dividing the nerve-ring in the disc;
or, which is virtually the same thing, while leaving
this intact, dividing all the nerves where the}^ pass
from it into the rays. In specimens mutilated by
severino: the nerves at the base of each of the five
rays, or by dividing the nerve ring between all the
rays, the animal loses all power of co-ordination
among its rays. When a common Star-fish is so
mutilated it does not crawl in the same determinate
manner as an unmutilated animal, but, if it moves
at all, it moves slowly and in various directions.
When inverted, the power of effecting the righting
manoeuvre is seen to be gravely impaired, although
eventually success is ahvays achieved. There is a
marked tendency, as compared with unmutilated
specimens, to a promiscuous distribution of spirals
and doublings, so that instead of a definite plan of
the manoeuvre beino^ formed from the first, as is
usually the case with unmutilated specimens, such
a plan is never formed at all ; among the five rays
there is a continual change of un-coordinated move-
ments, so that the righting seems to be eventually
effected by a mere accidental prepotency of some of
the righting movements over others. Appended is
a sketch of such un-coordinated movement, taken
from a specimen which for more than an hour had
been twisting its rays in various directions (Fig. 57).
Another sketch is appended to show a form of
bending which specimens mutilated as described
are very apt to manifest, especially just after the

STAR-FISH AND SEA-URCHINS.

297

operation. When placed upon their dorsal surface,
they turn up ail their rays with a peculiar and
exactly similar curve in each, which gives to the
animal a somewhat tulip-lilvc form (Fig. 58). This
form is never assumed by unmutilated specimens,
and in mutilated ones, although it may last for a
long time, it is never permanent. In detached rays

Fig. 5/

Un-coordinated movcm':>nts of a vStar-fish, in which the nerves of all the
rays have been divided.

this peculiar curve is also frequently exhibited ; but
if the nerve of such a ray is divided at any point in
its length, the curve is restricted to the distal
portion of the ray, and it stops abruptly at the line
of nerve-section. When entire Star- fish are mutilated
by a section of each nerve-trunk half-way up each
ray, and the animal is then placed upon its back,
the tetanic contractiju of the muscles in the rays

298 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

before mentioned as occurring under this form of
section in detached rays, has the effect, when now
occurring in all the rays, of elevating the disc from
the floor of the tank. This opisthotonous-like
spasm is not, however, permanent ; and the distal
ends of the rays forming adhesions to the floor of
the tank, the animal eventually rights itself, though

Fig. 58. Form freqnentl}- assumed by Soar-fi^h under similar ciramistances.

much more slowly than unmutilated specimens.
After it has righted itself, although it twists about
the distal portions of the rays, it does not begin to
craAvl for a long time, and when it does so, it crawls
in a slow and indeterminate manner. Star-fish
so mutilated, however, can ascend perpendicular
surfaces.

STAR-FISII AND SEA-URCHINS. 299

Tl]c loss of co-ordination between the rays caused
by division of the nerve-ring in the disc is rendered
most conspicuous in Brittle-stars, from the circum-
stance that in locomotion and in righting so much
here depends upon co-ordinated muscular contrac-
tion of the rays. Thus, for instance, when a Brittle-
star has its nerve-ring severed between each ray,
an interesting series of events follows. First, there
is a long period of. profound shock — spontaneity,
and even irritability, being almost suspended, and
the rays appearing to be rigid, as if in tetanic
spasm. After a time, feeble spontaneity returns — ■
the animal, however, not moving in any determinate
direction. Irritability also returns, but only for
the rays immediately irritated, stimulation of one
ray causing active writhing movements in that
ray, but not affecting, or only feebly affecting, the
other rays. The animal, therefore, is quite unable
to escape from the source of irritation, the aimless
movements of the ra3's now forming a very marked
contrast to the instantaneous and vigorous leaping
movements of escape which are manifested by
unmutilated specimens. Moreover, un mutilated
specimens will vigorously leap away, not only from
stimulation of the rays, but also from that of the
disc ; but those with their nerve-ring cut make no
attempts to escape, even from the most violent
stimulation of the disc. In other words, the disc is
entirely severed from all physiological connection
witli the rays.

If the nerve-ring be divided at two points, one
on either side of a ray, that ray becomes physio-

300 JELLY-FISH, STAR-FISH, AND SEA-UKCHINS.

logically separated from the rest of the organism.
If the two nerve-divisions are so placed as to in-
clude two ailjacent rays — i.e. if one cut is on one
side of a ray and the other on the further side of
an adjacent ray — then these two rays remain in
physiological continuity with one another, although
they suffer physiological separation from the other
three. When a Brittle-star is completely divided
into two portions, one portion having two arms and
the other three, both portions begin actively to turn
over on their backs, again upon their faces, again
upon their backs, and so on alternately for an in-
definite number of times. These movements arise
from the rays, under the influence of stimulation
caused by the section, seeking to perform their
natural movements of leaping, which however end,
on account of the weight of the other rays being
absent, in turninor themselves over. An entire
Brittle-star when placed on its back after division
of its nerve-rino^ is not able to rig^ht itself, owinor to
the destruction of co-ordination among its rays.
Astropecten, under similar circumstances, at first
bends its rays about in various ways, with a pre-
ponderant disposition to the tulip form, and keeps
its ambulacral feet in active movement. But after
half an hour, or an hour, the feet generally become
retracted and the rays nearly motionless — the
animal, like a Brittle-star, remaining permanently
on its back. In this, as in other species, the eflect
of dividing the nerve-ring on either side of a ray
is that of destroying its physiological connection
with the rest of the animal, the feet in that ray,

STAR-FISH AND SEA-URCHINS. 301

although still remaining feebly active, no longer
taking part in any co-ordinated movement — that
ray, therefore, being merely dragged along by the
others.

Under this division it only remains further to be
said, that section of the nerve-ring in the disc, or
the nerve-trunks of the rays, although, as we have
seen, so completely destroying physiological con-
tinuity in the rows of ambulacral feet and muscular
system of the animal, does not destroy physiological
continuity in the external nerve-plexus ; for how-
ever much the nerve-ring and nerve- trunks may
be injured, stimulation of the dorsal surface of the
animal throws all the ambulacral feet and all the
muscular system of the rays into active movement.
This fact proves that the ambulacra! feet and the
muscles are all held in nervous connection with one
another by the external plexus, without reference
to the integrity of the main nerve-trunks.

2. Echini. — Section of external surface of shell.
— If a cork-borer be applied to the external surface
of the shell of an Echinus, and rotated there till
the calcareous substance of the shell is reached,
and therefore a continuous circular section of the
over-lying tissues effected, it is invariably found
that the spines and pedicellarias within the circular
area are physiologically separated from the con-
tiguous spines and pedicellarige, as regards local
reflex excitability. That is to say, if any part of
this circular area be stimulated, all the spines and
pedicellarice within that area immediately respond
to the stimulation in the ordinary way; while none

302 JELLY-FISII, STAR-FISH, AN^D SEA-URCHINS.

of the spines or pcdicellariaB surrounding the area
are affected. Similarly, if any part of the shell
external to the circumscribed area be stimulated,
the spines and pedicellarije within that area are not
affected. These facts prove that the function which
is manifested by those appendages of localizing
and gathering round a seat of stimulation, is exclu-
sively dependent upon the external nerve-plexus.
It is needless to add that in this experiment it does
not signify of what size or shape or by what means
the physiological island is made, so long as the
destruction of the nervous plexus by a closed curve
of injury is rendered complete. In order to ascer-
tain whether, in the case of an unclosed curve of
injury, any irradiation of a stimulus would take
place round the ends of the curve, we made sundry
kinds of section. It is, however, needless to describe
these, for they all showed that, after injury of a
part of the plexus, there is no irradiation of the
stimulus round the ends of the injury. Thus, for
instance, if a short straight line of injury be made,
by drawing the point of a scalpel over the shell, say
along the equator of the animal, and if a stimulus
be afterwards applied on either side of that line,
even quite close to one of its ends, no effect will be
exerted on the spines or pedicellarijB on the other
side of the line. This complete inability of a
stimulus to escape round the ends of an injury,
forms a marked contrast to the almost unlimited
degree in which such escape takes place in the more
primitive nervous plexus of the Medusse.

Although the nervous connections on which the

STAR- FISH AND SEA-URCHINS. 303

spines and pcdiccllarire depend for their function of
localizino- and closino- round a seat of stimulation
are thus shown to be completely destroyed by
injury of the external plexus, other nervous connec-
tions, upon which another function of the spines
depends, are not in the smallest degree impaired by
Buch injury. The other function to which I allude
is that which brings about the general co-ordinated
action of all the spines for the purposes of locomo-
tion. That this function is not impaired by injury
of the external plexus is proved by the fact that
if the area within a closed line of injury on the
surface of the shell be strongly irritated, all the
spines over the whole surface begin to manifest
their peculiar bristling movements, and by this co-
ordinated action rapidly move the animal in a
straight line of escape from the source of irritation ;
the injury to the external plexus, although com-
pletely separating the spines enclosed by it from
their neighbouring spines as regards what may be
called their local function of seizinn^ the instrument
of stimulation, nevertheless leaves them in undis-
turbed connection with all the other spines in the
organism as regards what may be called their
universal function of locomotion.

Evidently, therefore, this more universal function
must depend upon some other set of nervous con-
nections; and experiment shows that these are dis-
tributed over all the internal surface of the shell.
Our mode of experimenting was to divide the
animal into two hemispheres, remove all the internal
oigan« of both hemispheres (these operations pro-

304 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

ducing no impairment of any of the functions of
the pedicels, spines, or peflicellari?e), and then to
paint with strong acid the inside of the shell — com-
pletely washing out the acid after about a quarter
of a minute's exposure. The results of a number
of experiments conducted on this method may be
thus epitomized : —

The effect of painting the back or inside of the
shell with strong acid {e.g. pure HCl) is that of at
first strongly stimulating the spines into bristling-
movements, and soon afterwards reducing them to
a state of quiescence, in which they lie more or less
tiat, and in a peculiarly confused manner that
closely resembles the appearance of corn wdien
" laid " by the wind. The spines have now entirely
lost both their spontaneity and their power of
responding to a stimulus applied on the external
surface of the shell — i.e. their local reflex excita-
bility, or powder of closing in upon a source of irri-
tation. These effects may be produced over the
whole external surface of the shell, by painting
the whole of the internal surface ; but if any part
of the internal surface be left unpainted, the cor-
i-esponding part of the external surface remains
uninjured. Conversely, if all the internal surface
be left unpainted except in certain lines or patches,
it will only be corresponding lines and patches on
the external surface that suffer injury. It makes
no difference wdiether these lines or patches be
painted in the course of the ambulacral feet, or
anywhere in the inter-ambulacral spaces.

The above remarks, which have reference to the

STAR-FISH AND SEA-URCHINS. 305

spines, apply equally to the pedlcellarire, except
that their s[)ontaneity and reiiex irritability are not
destroyed, but only impaired.

Some hours alter the operation it usually happens
that the spontaneity and reiiex irritability of the
spines return, though in a feeble degree, and also
those of the pedicellari^B, in a more marked degree.
This applies especially to the reflex irritability of
the pedicellarise ; for while their spontaneity does
not return in full degree, their reflex irritability
docs — or almost in full degree.

These experiments, therefore, seem to point to
the conclusions — 1st, that the o'eneral co-ordination
of the spines is dependent on the integrity of an
internal nerve-plexus ; 2nd, tiiat the internal plexus
is everywhere in intimate connection with the ex-
ternal; and ord, that complete destruction of the
former, while profoundly influencing the functions
of the latter, nevertheless does not wholly destroy
them.

Professor Ewart therefore undertook carefully to
examine the internal surface of the shell, to see
whether any evidence of this internal nervous
plexus could be found microscopically, and, after a
great deal of trouble, he has succeeded in doing so.
But as he has not yet published his results, I shall
not forestall them further than to say that this
internal plexus spreads all over the inside of the
shell, and is everywhere in communication with the
external plexus by means of fibres which pass be-
tween tlie sides of the hexagonal plates of which
the shell of the animal is composed. Thus we can

o;)6 JELLY-FISH, STAR-FIGH, AND SEA-UKCHINS.

understand ho'vV it is that when a portion of the
external plexus is isolated from the rest of that
plexus as a residt of the cork-borer experiment, the
island still remains in communication with the
nerve-centres which preside over the co-ordination
of the spines, as proved by the fact of the Echinus
using its spines to escape from irritation applied to
the area included within the circle of injury to the
external plexus produced b}^ the cork-borer.

Now, where are these nerve-centres situated ?
We have just seen that we have evidence of the
presence of such centres somewhere in an Echinus,
seeing that all the spines exhibit such perfect
co-ordination in their movements. Where, then,
are these centres ?

Seeinor that in a Star-fish the ravs are co-ordinated
in their action by means of the pentagonal ring in
the disc, analogy pointed to the nervous ring round
the mouth of an Echinus as the part of the nervous
system which most probably presides over the
co-ordinated action of the spines. Accordingly, we
tried the effect of removing this nervous ring, and
immediately obtained conclusive proof that this was
the centre of which we were in search ; for as
soon as the nervous ring was removed, the Echinus
lost, completely and permanently, all power of co-
ordination among its spines. That is to say, after
this operation these organs were never again used
by the animal for the purposes of locomotion, and
no matter how severe an injury we applied, the
Echinus, when placed on a table, did not seek to
escape. But the spines were not wholly paralyzed,

STAR-FISH AND SEA-URCTIINS. 307

or motionless. On the contrary, their power of
spontaneous movement continued unimpaired, as
did also their power of closing round a seat of
irritation on the external surface of the sliell. The
same remark applies to the pedicellarine, and the
explanation is simple. It is the external nervous
plexus which holds all the spines and pedicellariee in
comnumication with one another as by a network;
so that when any part of this network is irritated,
all the spines and pedicellari?e in the neighbourhood
move over to the seat of irritation. On the other
hand, it is the internal plexus which serves to unite
all the spines to the nerve-centre which surrounds
the mouth, and which alone is competent to co-
ordinate the action of all the spines for the purposes
of locomotion.

It remains to consider whether the ambulacral
feet exhibit any general co-c^linated action, and, if
so, whether this likewise depends upon the same
nerve-centre.

The fact already mentioned, that during pro-
gression an Echinus uses some of its feet for crawl-
ing and others for feeling its way, is enough to
suggest that all the feet are co-ordinated by a
nerve-centre. But in order to be quite sure about
the fact of there being a general co-ordination among
all the feet, we tried the following experiments.

I have already described the rii-htino,- movements
which are performed by an Echinus when the
animal is inverted, and it will be remembered that
in this animal the manoeuvre is effected by means
of the fet;t alone. At first sicht this midit almost

308 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

seem suMlcient to prove the fact of a general co-
ordination among the feet ; but further reflection
will show that it is not so. For the feet being all
arranged in rec>u]ar series, when one row begins to
effect the rotation of the globe, it may very well be
that its further rotation in the same direction is due
only to the fact that the slight tilt produced by the
jmlling of the tirst feet in the series A, B, C gives
the next feet in the series D, E, F an opportunity
of reaching the floor of the tank; their adhesions
being established, they would tend by their pulling
to increase still furtlier the tilt of the globe, thus
giving the next feet in the series an oppoi'tunity of
fastening to the floor of the tank, and so on. In
order, therefore, to see whether these righting
movements were due to nervous co-ordination
among the feet, or merely to the accident of the
serial arrangement of the feet, we tried the experi-
ments which I shall now detail.

First of all we took an Echinus, and by means of
a thread suspended it upside-down in a tank of
water half-way up the side of the tank, and in such
a way that only the feet on one side of the ab-oral
pole were able to reach the perpendicular wall of
the tank. These feet as quickly as possible estab-
lished their adhesions to the pei-pendicular wall,
and, the thread being then removed, the Echinus
was left sticking to the side of the tank in an in-
verted position by means of the ab-oral ends of two
adjacent feet-rows (Fig. 50). Under these circum-
stances, as we should expect from the previous ex-
periments, the animal sets about righting itself as

STAR- FISH AND SEA-URCIIINS. 309

quicAly as possible. Now, if the righting action of
the Icct were entirely and only of a serial character,
the rigliiing would require to be performed by rear-
ing the animal upwards; the etfect of foot after
foot in the same rows being applied in succession to
the side of the tank, would require to be that of
rotating: the lobular shell ao-ainst the side of the
tank towards the surface of the Avater, and therefore
against the action of gravity. This is sometimes
clone, Avhich proves that the energy required to per-
form the feat is not more than a healthy P^chinus
can expend. But much more frequently the
Echinus adopts another device, and the only one by
which it is possible for him to attain his pui'pose
without the labour of rotating upwards: he rotates
laterally and downwards in the form of a spiral.
Thus, let us call the five feet-rows, 1, 2, 3, 4, and 5
(Figs. 59, 60, 61), and suppose that 1 and 2 are in
use near their ab-oral ends in holding the animal
inverted against the perpendicular side of a tank.
The downward spiral rotation would then be
eflected by gradually releasing the outer feet in row
1, and simultaneously attaching the outer feet in
row 2 (i.e. those nearest to row 3, and furthest from
row 1), as far as possible to the outer side of that
row. The eflcc' of this is to make the globe roll far
enough to that side to enable the inner feet of row^
o {i.e. those nearest to row 2), when fully protruded,
to touch the side of the tank. They establish their
adhesions, and the residue of feet in row 1, now
leaving go their hold, these new adhesions serve to
roll the globe still further round in the same

21

310 JELLY-FISH, STAR-

FISH, AND SEA-UKCHINS.

STAR-FISII AND SEA-URCHINS.

311

direction of lateral rotation, and so the process pro-
ceeds from row to row ; but the globe does not
merely roll along in a horizontal direction, or at the
same level in the water, for each new row that
comes into action takes care, so to speak, that the

Fig 61.
Figs. 59, 60, and 61 are righting movements of Echinns on a perpendicular suiface.

feet which it employs shall be tliose which are as
far below the level of the feet in the row last em-
ployed as their length wdien fully protruded (i.e.
their power of touching the tank) renders possible.
The rotation of the orlobe thus becomes a double

312 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

one, lateral and downwards, till the animal assumes
its normal position with its oral pole against the
perpendicular tank wall. So considerable is the
rotation in the downward direction, that the normal
position is generally attained before one complete
lateral, or equatorial, rotation is completed.

The result of this experiment, therefore, implies
that the righting movements are due to something
more than the merely successive action of the seiies
of feet to which the work of righting the animal
may happen to be given. The same conclusion is
pointed to by the results of the following experi-
ment.

A number of vigorous Echini were thoroughly
shaved with a scalpel over the whole half of one
hemispliere, i.e. the half from the equator to the
oral pole. They Avere then inverted on their ab-oral
poles. The object of the experiment Avas to see
what the Echini which were thus deprived of the
lower half of three feet-rows would do when, in
executing their righting manoeuvres, they attained
to the equatorial position and then found no feet
wherewith to continue the manoeuvre. The result
of this experiment was first of all to show us that
the Echini invariably chose the unmutilated feet-
rows wherewith to right themselves. Probably this
is to be explained, either by the general principle
to which the escape from injury is due — viz. that
injury inflicted on one side of an Echinoderm
stimulates into increased activity the locomotor
organs of the opposite side, — or by the consideration
that destruction of the lower half of a row very

STAR- FISH AND SEA-UllCHINS. 313

probaMy ineluces some degree of shock in the
remaining half, and so leaves the corresponding
parts of the unmutilated rows prepotent over the
mutilated one. Be tliis as it may, however, we
found that the difficulty was easily overcome by
tilting the animal over upon its mutilated feet-rows
sufficiently far to prevent the unmutilated rows
from reaching the floor of the tank. When held
steadily in this position for a short time, the muti-
lated rows established their adhesions, and the
Echinus was then left to itself Under these cir-
cumstances an Echinus will always continue the
manoeuvre along the mutilated feet-rows with
which it was begun, till the globe reaches the posi-
tion of resting upon its equator, and therefore
arrives at the line where the shaved area com-
mences. The animal then remains for hours in this
position, with a gradual but continuous motion
backwards, which appears to be due to the suc-
cessive slipping of the spines — these organs in the
righting movements being always used as props for
the ambulacral feet to pull against while rearing
the globe to its equatorial position, and in perform-
ing this function on a slate floor the spines are
liable often to slip. The only other motion ex-
hibited by Echini thus situated is that of a slow
rolling movement, now to one side and now to
another, according to the prepotency of the pull
exerted by this or that row of ambulacral feet.
Things continue in this way until the slow back-
ward movement happens to bring the animal
against some side of the tank, when the uninjured

3 14 JELLY-FISH, STAR-IISII, AND SEA-URCHINS.

rows of ainbulacral feet immediately adhere to the
surface and rotate the animal upwards or horizon-
tally, until it attains the normal position. But if
care be taken to prevent contact with any side of
the tank, the mutilated Echinus will remain propped
on its equator for days ; it never adopts the simple
expedient of reversing the action of its mutilated
feet- rows, so as to bring the globe again upon its
ab-oral pole and get its unmutilated feet- rows into
action.

From this we may conclude that the righting
movements of the pedicels are due, not to the merely
serial action of the pedicels, but to their co-ordina-
tion by a nerve-centre acting under a stimulus
so pplied by a sense of gravity ; for if the move-
ments of the pedicels were merely of a serial
character, we should not expect that the equatorial
position, having been attained under these circum-
stances, should be permanently maintained. We
should not expect this, because after a while the
pedicels, which are engaged in maintaining the
globe in its equatorial position, must become ex-
hausted and relax their hold, when those next
behind in the series would lay hold of the bottom
of the tank, and so on, the rotation of the globe
thus proceeding in the opposite direction to that
in which it had previously taken place. On the
other hand, if the righting movements of the pedi-
cels are due to co-ordination proceeding from a
nerve-centre acting under a sense of gravity, we
should expect the animal under the circumstajices
mentioned to remain permanently reared upon its

STAR-FISH AND SEA-URCHINS. 315

eqTiator; for this would show that the nerve-centre
was always persistently, though fruitlessly, endea-
vouring to co-ordinate the action of the absent feet.

Further, as proof that the ambulacral feet of
Echinus are under the control of some centralizinof
apparatus when executing the righting manoeuvre,
we may state one other fact. When the righting
maoenuvre is nearly completed by the rows engaged
in executing it, the lower feet in the other rows
become strongly protruded and curved downwards,
in anticipation of shortly coming into contact with
the floor of the tank when the riohtinoj manoeuvre
shall have been completed (see Fig. 52, p. 280).
This fact tends to show that all the ambulacral feet
of the animal are, like all the spines, held in mutual
communication with one another by some central-
izing mechanism.

But the best proof of all that the feet in executing
the righting manoeuvre are under the influence of
a co-ordinating centre, is one that arose from an
experiment suggested to me by Mr. Francis Darwin,
and which I shall now describe. Mr. Darwin
having kindlj^ sent the apparatus which his father
and himself had used in their experiments on
the geotropism of plants, it was employed thus.
A healthy Echinus was placed in a large bottle
filled to the brim with sea- water, and having been
inverted on the bottom of the bottle, it was allowed
in that position to establish its adhesions. The
bottle was then corked and mounted on an upright
wheel of the apparatus whereby, by means of clock-
work, it could be kept in continual slow rotation

016 JELLY-FISH; STAR-FJSrr, AND SEA-URCHINS.

in a vertical plane. The object of this was to
ascertain whether the continuous rotation in a
vertical plane would prevent the animal from right-
ing itseU' (because confusing the nerve-centres
which, under ordinary circumstances, could feci by
their sense of gravity wliich was up and which
was down), or would still allow the animal to right
itself (because not interfering with the serial action
of the feet). AVell, it was found that this rotation
of the whole animal in a vertical plane entirely
])re vented the righting movements during any
length of time that it might be continued, and that
tiiese movements were immediately resumed as
soon as the rotation was allowed to cease. This,
moreover, was the case, no matter what phase of
the righting manoeuvre the Echinus might have
reached at the moment when the I'otation began.
Thus, for instance, if the globe were allowed to
liave reached the position of resting on its equator
befoi-e the rotation was commenced, the Echinus
would remain motionless, holding on with its equa-
torial feet, so long as the rotation was kept up.

Therefore, there can be no question that the am-
bulacral feet are all under the influence of a co-
O'dinating nerve-centre, quite as much as are the
spines. But, on the other hand, experiments show
that the centre in this case is not of so localized a
character as it is in the case of the spines ; for
when the nerve-ring is cut out, the co-ordina-
tion of the feet, although impaired, is not Avholly
destroyed. Take, for instance, the case of the
righting manoiuvre. The effect of cutting out the

STAR- FISH AND SEA-URCHINS. 817

nerve-ling is that of entiicly destroying the ability
to peiforni this manoRiivre in the case of the majority
of specimens ; nevertheless about one in ten continue
able to perform it. Again, if an Echinus is divided
into two hemispheres by an incision carried from pole
to pole through any meridian, the two hemispheres
wiU live for days, crawling about in the same
manner as entire animals; if their ocular plates
are not injured, they seek the light, and when
inverted they right themselves. The same observa-
tions apply to smaller segments, and even to single
detaclied rows of ambulacral feet. The latter are,
of course, analogous to the single detached rays of
a Star-fish, so far as the S3^stem of ambulacral feet
is concerned ; but, looking to the more complicated
apparatus of locomotion (spines and pedicellariye),
as well as to the rigid consistence and awkward
shape of the segment — standing erect, instead of
lying flat — the appearance presented by such a seg-
ment in locomotion is much more curious, if not
surprising, than that presented by the analogous
part of a Star-fish under similar circumstances. It
is still more surprising that such a fifth-part seg-
ment of an Echinus will, when proj'jped up on its
ab-oral pole (Fig. 62), right itself (Fig. 03) after
the manner of larger segments or entire animals.
They, however, experience more difficulty in doing
so, and very often, or indeed generally, fail to
coujplete the manoeuvre.

On the whole, then, we may conclude that the
nervous system of an Echinus consists (1) of an
external plexus which serves to unite all the feet,

818 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

,iiii„Hiiiuiiiiiiiiiiiiiiiiiiiiiii||MMmiuiiiiiiiiiiiiiilllllllillllilllllllllliiiHW

Figs. 62 and 63.-Higbting and ambulacral movements of severed segments
of Ecliinuo.

STAR-FISH AND SEA-Ur.CIIINS. 319

spines, and pedicellarire together, so that they all
ai)proxiinate a point of irritation sifAiated anywhere
in that plexus ; (2) of an internal nervous plexus
which is everywlicre in communication through the
thickness of the shell with the external, and the
function of which is that of bringing the feet, spines,
and probably also the pedicellarise into relation
with the o'reat co-ordinatino^ nerve-centre situated

O CD

round the mouth ; (3) of central nervous matter
which is mainly gathered round the mouth, and
there presides exclusively over the co-ordinated
action of the spines, and in large part also over
the co-ordinated action of the feet, but which is
further in part distributed along the courses of the
main nerve-trunks, and so secures co-ordination of
ieet even in separated segments of the animal.

Special Senses.

Before concluding, I must say a few words on
the experiments whereby we sought to test for the
presence in Echinoderms of the special senses of
sight and smell.

We have found unequivocal evidence of the Star-
fish (with the exception of the Brittle-stars) and
the Echini manifesting a strong disposition to crawl
tow^ards, and remain in, the light. Thus, if a large
tank be completely darkened, except at one end
where a narrow slit of light is admitted, and if a
number of Star-fish and Echini be scattered over
the floor of the tank, in a few hours the whole
number, with the exception of perhaps a few per

320 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

coiit, will be found congfue^'.ated in the narrow slit
of light. The source we used was diffused day-
light, which was admitted through two sheets of
glass, so tliat the thciTiial rays might be considered
practically excluded. The intensit>j of the light
which the Echinoderms are able to perceive may be
very feeble indeed ; for in our first experiments we
boarded up the face of the tank with ordinary pine-
wood, in order to exclude the light over all parts
of the tank except at one narrow slit between two
of the boards. On takino- down the boards we
found, indeed, the majority of tlie specimens in or
near the slit of light; but we also found a number
of other specimens gatliering all the way along the
glass face of the tank that was immediately behind
the pine-boards. On repeating the experiment
with blackened boards, this was never found to be
the case ; so there can be no doubt that in the first
experiments the animals were attracted by the
faint glimmer of the white boards, as illuminated
by the veiy small amount of light scattered from
the narrow slit through a tank, all the other sides
of which were black slate. Indeed, towards the
end of tlie tank, where some of the specimens were
found, so feeble must have been the intensity of
this glimmer, that we doubt whether even human
eyes could have discerned it very distinctly. Owing
to the prisms at our command not having sufficient
dispersive power for the experiments, and not wish-
ing to rely on the uncertain method of employing
coloured glass, we were unable to ascertain how the
Echinoderms might be affected by different rays.

STAR- FISH AND SEA-URCHINS. 321

On removing with a pointed scalpel the eye-spots
from a nunber of Star-fish and Echini, without
othervvise injuring t1ie animals, the latter no longer
crawled towards the liifht, even thouo^h this were
admitted to the tink in abundance; but they
crawled promiscuously in all directions. On the
other hand, if only one oat of the five eye-spots were
left intact, the animals crawled towards the light
as before. It may be added that single detached
rays of Star-fish and fifth-part segments of Echini
crawl towards the light in the same manner as
entire animals, provided, of course, that the eye-spot
is not injured.

The presence of a sense of smell in Star-fish was
proved by keeping some of these animals for several
days in a tank without food, and then presenting
them with small pieces of shell-fish. The Star-fish
immediately perceived the proximity of food, as
shown by their immediately crawling towards it.
Moreover, if a small piece of the food were held in
a pair of forceps and gently withdrawn as the Star-
fish approached it, the Minimal could be led about
the floor of the tank in any direction, just as a
hungry dog could be led about by continually
withdrawing from his nose a piece of meat as he
continually follows it up. This experiment, how-
ever, was only successful with Star-fish which had
been kept fasting for several days ; freshly caught
Star-fish were not nearly so keen in their manifesta-
tions, and indeed in many cases did not notice the
food at all.

Desiring to ascertain whether the sense of smell

322 JELLY-FISH, STAR-FISH, AND SEA-URCHINS.

were localized in any particular organs, as we had
found to be the case with the sense of sight, I first
tried the effect of removing the five ocelli. This
produced no difference in the result of the above
experiment witli hungry Star-fish, and therefore I
next tried the effect of cutting oft* the tips of the
rays. The Star-fish behaving as before, I then pro-
gressively truncated the rays, and thus eventually
found that the olfactory sense was etjually dis-
tributed throughout their length. The question,
however, still remained whether it was equally dis-
tributed over both the upper and the lower sufifaces.
I therefore tried the eff"ect of varnishing the upper
surface. The Star-fish continued to find its food as
before, wdiich showed that the sense of smell was
distributed along the lower surface. I could not try
the converse experiment of varnishing this surface,
because I should thereby have hindered the action
of the ambulacral feet. But by another method
I was able nearly as well to show that the upper
surface does not participate in smelling. This
method consisted in placing a piece of shell-fish
upon the upper surface and allowing it to rest there.
When this was done, the Star-fish made no attempt
to remove the morsel of food by brushing it off" with
the tips of its rays, as is the habit of the animal
when any irritating substance is ^^pj^lied to this
surface. Therefore I conclude that the upper or
dorsal surface of a Star-fish takes no part in minis-
tering to the sense of smell, which by the experi-
inent of varnishing this sui-face, and also by that
of progressively truncating the rays, is proved to

STAR-FISH AND SEA-URCHINS. 323

be distributed over the whole of the ventral or
lower surface of the animal. For I must add that
severed rays behave in all these respects like the
entire organisms, although they are disconnected
from the mouth and disc.

As this chapter has already extended to so great
a length, I omit from it any account of some further
experiments which I tried concerning the effects of
nerve-poisons upon the Echinodermata. A full
record of these experiments may be found in the
publications of the Linnean Society.

FINIS.

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HE ICE AGE IN NORTH AMERICA, and its

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"The author has seen with his own eyes the most important phenomena of the Ice
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is combined with a broad, scientific, and philosophic method, without abandoning for
a moment the purely scientific character. Professor Wright has contrived to give tlie
whole a philosophical direction which lends interest and inspiration to it, and which in
the chapters on Man and the Glacial Period rises to something like dramatic intensity."
— The Indepcndefit.

". . . To the great advance that has been made in late years in the accuracy and
cheapness of processes of photographic reproduction is due a further signal advantage
that Dr. Wright's work possesses over his predecessors'. He has thus been able to
illustrate most of the natural phenomena to which he refers by views taken in the field,
many of which have been genciously loaned by the United States Geological Survey,
in some rases from unpublished material ; and he has admirably supplemented them by
numerous maps and diagrams." — 7 he Nation.

M

AN AND THE GLACIAL PERIOD. By G.
Frederick Wright, D. D., LL. D., author of "The Ice
Age in North America," " Logic of Christian Evidences," etc.
No. 69, International Scientific Series. With numerous Illus-
trations. i2mo. Cloth, $1.75.

Every one is interested in ancestry, yet the roots of family trees have not
struck down to the Glacial period, and we are left to wonder regarding the
manners and customs of our ancestors in the remote age of ice. Who and
what these ancestors were, is told us in simple, entertaining, popular style
by Professor Wright, and his fascinating narrative is re-enforced by a multi-
tude of illustrations.

New York : D. APPLETON & CO., i, 3, & 5 Bond Street.

E

D. APPLETON & CO.'S PUBLICATIONS.

SSAYS UPON SOME CONTROVERTED

QUESTIONS. By Thomas li. Huxley, F. R. S., author

of " Man's Place in Nature," etc. i2mo. Cloth, $2.00.

" Professor Huxley is one of the most vigorous and uncompromising polemics of
tlie age. He is admittedly also one of the very ablest. In tliat debatable land which
touches the confines of science on the one hand and the confines of religion on the
other, there is no living man who can be called his supeiior. Professor Huxley takes
n*) mysterious or incomprehensible position. He plants himself on facts. There is,
he contends, no other safe or solid position. . . . He has compelled attention to the
truths of scienje. He has made religion more intelligent. He lias helped us to see
that science and religion are not mutually destructive — that the God of Nature and the
God of the Bible are one God." — Ckristmn at Work.

' . . . Mr. Hu.\ley's literary style, also, is singularly lucid, polished, graceful, and
strong. There is no living writer of English more 'cunning offence' in dialectics;
none who has a better gift for clothing his ideas in perspicuous and elegant language.
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ness of a tUoroiigh scholar." — I Jiiladelphia BiiLetiyi.

T

'HE NATURALIST IN LA PLATA. By C.
H. Hudson, C. M. Z. S., joint author of " Argentine Ornithol-
ogy." With 27 Illustrations. 8vo, 388 pages. Cloth, $4.00.

" Mr. Hudson is not only a clever naturalist, but he po.ssesses the rare gift of in-
teresting his readers in whatever attracts him, and of being dissatisfied with mere ob-
servation unless it enables him to philosophize as well. With his lucid accounts of
bird, beast, and insect, no one will fail to be delighted." — Loiidoti Academy.

" Mr. Hudson is a scientist, it is true, but apparently not enough of a scientist to
have lost the faculty of wonder and the knack of making readers wonder with him.
He has worked on an ornithology of the Argentine States, but his case appears to be
that of Audubon, and the results of avoiding the drudgery of science the same. At
least, he has so many new and interesting and piquant things to tell about the insects,
birds, and beasts found on the pampas, that few books of the sort, if any, which have
been published smce the work of Belt appeared, can vie with it in charm." — New
York Times.

NEW EDITION OF

RAGMEN TS OF SCIENCE. By John Tyndall,

F. R.S., author of "Sound," "Heat as a Mode of Motion,"
etc. Revised and enlarged edition. 2 vols. i2mo. Cloth, $4.00.

The first edition of Professor Tyndall's "Fragments of Science" was
published some twenty years ago as a single volume, which was made up of
a score or more of his detached essays, addresses, and reviews. The book
was afterward revised, some of the papers recast, and from time to time new
ones added until, the size of the work becoming somewhat unwieldy, the
present two-volume edition was decided upon. This contains fifteen addi-
tional papers, and represents the author's latest changes and revisions. The
volumes are uniform with " New Fragments, recently issued, and the three
together include all the occasional writings which their author has decided to
preserve in permanent form.

F

New York . D. APPLETON & CO., i, 3, & 5 Bond Street.

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VOLUTION IN SCIENCE, PHILOSOPHY,

AND ART. A Series of Seventeen Lectures and Discussions

before the Brooklyn Ethical Association. With 3 Portraits.

466 pages. i2iriO. Cloth, $2.00. Separate Lectures, in pam=

phlet form, 10 cents each.

These popular essays, by some of the ablest exponents of the doctrine of

evolution in this country, will be read with pleasure and profit by all lovers

of good literature and suggestive thought. The principle of evolution, being

universal, admits of a great diversity of applications and illustrations ; some

of those appearing in the present volume are distinctively fresh and new.

CONTENTS.

1. Alfred Russel Wallace By Edward D. Cope, Ph. D.

2. Ernst Haeckel By Thaddeus B. Wakeman.

3. The Scientific Method By Francis E. Abbot, Ph.D.

4. Herbert Spencer's Synthetic Philosophy. By Benj. F. Underwood.

^. Evolution of Chemistry By Robert G. EccLES, M. D.

6. Evolution of Electric and Magnetic Physics.

By Arthur E. Kennelly.
'J. Evolution of Botany By Fred J. Wulling, Ph. G.

8. Zoology as related to Evolution ... By Rev. John C. Kimball.

9. Form and Color in Nature .... By William Potts.

10. Optics as related to Evolution . . . By L. A. W. Alleman, M. D.

11. Evolution of Art By John A. Taylor.

Y-z. Evolution of Architecture EyRev. John W. Chadwick.

XT,. Evolution of Sculpture By Prof. Thomas Davidson.

14. Evolution of Painting By Forrest P. Rundell.

15. Evolution of Mtisic By Z. Sidney Sampson.

16. Life as a Fine Art By Lewis G. Janes, M. D.

17. The Doctrine of Evolutiofi : its Scope and Influence.

By Prof. John Fiske.

"A valuable series." — Chicago Evening fournal.

'The addresses include some of the most important presentations and epitomes pii?>
lished in America. They are all upon important subjects, are prepared with preatcare,
and are delivered for the most part by highly eminent authorities " — Public Opiuiou.

" As a popular exposition of the latest phases of evolution this series is thorough and
authoritative. " — Cincinnati Times-Star.

New York : D. APPLETON & CO., i, 3, & 5 Bond Street.

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D. APPLETON /?: CO.'S PUBLICATIONS.

£IV FRAGMENTS. By John Tyndall, F. R. S.,

author of " Fragments of Science," " Heat as a Mode of Motion,"
etc. i2mo. 500 pages. Cloth, $2.00.

Among: the subjects treated in this volume are "The Sabbath," " Life in
the Alps," "The Rainbow and its Congeners," "Common Water," and
"Atoms, Molecules, and Ether- Waves." In addition to the popular treat-
ment of scientific themes, the author devotes several chapters to biographical
sketches of the utmost interest, including studies of Count Rumford and
Thomas Young, and chapters on " Louis Pasteur, his Life and Labors," and
" Personal Recollections of Thomas Carlyle."

"Tyndall is the happiest combination of the lover of nature and the lover of science,
and these fragments are admirable examples of his delightful style, and pioofs of his
comprehensive intellect " — 1 kiladclphia Evening Bulletm.

"The name of this illustrious scientist and lUleraieur\% known wherever the Eng-
lish language is the mother tongue, or is even freely spoken. Whatever he does or
says comes with a stamp of authority as from one who speaks with power, knowing
whereof he affirms. He is able and effective, both as a talker and writer, as scientist
or teacher. I'o those who know anything of Prof. Tyndall's life and labors, scientific
or literary, it is superfluous to say that his utterances bring his hearers or readers face
to face with the latest knowledge on the subject he discusses." — New York Commer-
cial A dvertiser.

M

M^-

ORAL TEACHINGS OF SCIENCE. By Ara-
bella B, Buckley, author of "The Fairy-Land of Science,"
" Life and her Children," etc. i2mo. Cloth, 75 cents.

" The book is intended for readers who would not take up an elaborate philosophical
work — those who, feeling puzzled and adrift in the present chaos of opinion, may
welcome even a partial solution, from a scientific point of view, of the difficulties which
oppress their minds." — Frotn the Preface.

''AX MULLER AND THE SCIENCE OF

-^^^ LANGUAGE. A Criticism. By William Dwight Whitney,

Professor in Yale University. i2mo. 79 pages. Paper cover,

50 cents.

This critique relates to the new edition of Prof. Muller's well-known work
on Language. " For many," says Prof. Whitney, in his preface, " the book
has been their first introduction to linguistic study ; and doubtless to a large
proportion of English-speaking readers, especially, it is still the principal and
most authoritative text-book of that study, as regards both methods and re-
sults. A work holding such a position calls for careful criticism, that it may
not be trusted where it is untrustworthy, and so do harm to the science
which it was intended to help."

"This caustic review of Max IMiiller's latest edition of his 'Science of Language*
will command attention for more and higher merits than its brilliant criticism. It up-
holds a theory of language and of its development which, though not taught by Max
Miiller, is held by the great masters of linguistic science. The reader not versed in the
science, nor well read in its controversial literature, will get from this brochure a con-
ception of the critical points of the subject which he might miss in the reading of many
larger and more systematic treatises."— 7^,^^ Jndependent, New York.

New York : D. APPLETON & CO., i, 3, & 5 Bond Street.

D. APPLETON & CO.'S PUBLICATIONS.

MODERN SCIENCE SERIES.
Edited by Sir John Lubbock, Bart., F. R S.

The works to be comprised in the " Modern Science Series" are primarily not for
the student, nor for the young, but for the educated layman who needs to know the
present state and result o! scientific investigation, and who has neither time nor inclina-
tion to become a specialist on the subject which arouses his interest. Each book will
be complete in itself, and, while thoroughly scientific in treatment, its subject will as
far as possible be j^resented in language divested of needless technicalities. Illustra-
tions will be given wheiever needed by the text. The following are the volumes thus
far issued. Others are in preparation.

T

HE CA USE OE AN ICE AGE. By Sir Robert
Ball, LL. D., F. R. S., Royal Astronomer of Ireland, author of
"Starland." i2mo. Cloth, $i.oo.

" Sir Robert Ball's book is, as a matter of course, admirably written. Though but a
small one, it is a most important contribution to geology." — Lofidon Saturday Review.

" A fascinating subject, cleverly related and almost colloquially discussed." — Phila-
delphia Public Ledger.

7^HE HORSE: A Study in Natural History. By
William H. Flower, C. B., Director in the British Natural
History Museum. With 27 Illustrations. i2mo. Cloth, $1.00.

" The author admits that there are 3,800 separate treatises on the horse already pub-
lished, but he thinks that he can add something to the amount of useful information
now before the public, and that something not heretofore written will be found in this
book. The volume gives a large amount of information, both scientific and practical,
on the noble animal of which it treats." — New York Coi7i})tercial Advertiser.

T

HE OAK: A Study in Botany. By H. Marshall
Ward, F. R. S. With 53 Illustrations. i2mo. Cloth, $i.co.

" \n excellent volume for young persons with a taste for scientific studies, becacre
it will lead them from the contemplation of superficial appearances and those gcnei alities
which arc so misleading to the immature mind, to a consideration of the methods of
systematic investigation." — Boston Beacofi.

" From the acorn to the timber which has figured so gloriously in English ships
and houses, the tree is fully described, and all its living and preserved be.tuties ; r.d
virtues, in nature and in construction, are recounted and pictured." — Brooklyn Ea^ie.

PTHNOLOGY IN EOIKLORE. By George

-^— ^ Lawrence Gomme, F. S. A., President of the Folklore Society,

etc. i2mo. Cloth, $1.00.

This book is an attempt to ascertain and set forth the principles upon
which folklore may be classified, in order to arrive at some of the results
which should follow its study, giving the subject the importance it deserves
in connection with researches in ethnology.

New York: D. APPLETON & CO., r, 3, c^- 5 Bond Street.

OL377.S4 R65 1893

hM^ hsi, s(,„ ),sl, ,n.|
Harvard MCZ Library

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