EE -STATEMENT OF THE CELL THEOKY,

WITH APPLICATIONS TO THE

MORPHOLOGY, CLASSIFICATION, AND PHYSIOLOGY OF
PROTISTS PLANTS, AND ANIMALS.

TOGETHER WITH AN

HYPOTHESIS OF CELL-STRUCTURE AND AN HYPOTHESIS

OF CONTRACTILITY. ' -

WITH PLATE

By PATRICK GEDDES.

Rrprivtcdfroiii the Proceedings oftii'e Royal Society of Juhul'inyh,
vol. Icif:, 1883-84.)

EE-STATEMENT OF THE CELL THEOEY,

WITH APPLICATIONS TO THE

M0KPH0L0GY, CLASSIFICATION, AND PHYSIOLOGY OF
PEOTISTS, PLANTS, AND ANIMALS.

TOGETHER WITH AN

HYPOTHESIS OF CELL-STRUCTURE, AND AN HYPOTHESIS
OF CONTRACTILITY.

WITH PLATE.

By PATEICK GEDDES.

(Reprinted from the Proceedings of the Royal Society of Edinburgh,
vol. xii, 1883-84.)

A Ke-Staternent of the Cell Theory, with Applications to
the Morphology, Classification, and Physiology of Protists,
Plants, and Animals. Together with an Hypothesis of
Cell-Structure, and an Hypothesis of Contractility.* By
Patrick Geddes. (Plate IV.)

(Communicated '3d December 1883.)

Position and Importance of the Cell Theory in Morphology. —
Vast though is the literature of vegetable and animal morphology,
it becomes more readily grasped than that perhaps of any other
science, when we classify it in relation to the few great works which
initiated and for ever mark the successive waves of advance. Thus
of the early pre-morphological or encyclopaedic stage, when materials
were being little more than heaped together, the works of Pliny or
Gesner may be taken as types, to which the other encyclopaedias of
Natural History by Jonston, &c, furnish at first mere supplements.
The Systema Natural of Linnaeus closes the old and marks a new
era, and initiates that systematic enumeration of the flora and fauna
of the globe which has since made such vast progress. All subse-
quent systematic literature, no matter how important, no matter how
much exceeding in quantity of new forms, involves no essential, no
qualitative advance : thus the greater part of the proceedings of such

* Prelim. Note in Zool. Amciger, No. 146, 1SS3.

RSI 4-^

Proceedings of the Royal Society. 267

Societies as the Zoological or the Linnean, such new and important
faunistic literature as that contained in the magnificent volumes of
the " Challenger" Expedition, or even the greatest systematic works,
find their highest place not as superseding, hut as supplementing
the fundamental classic of Linnaeus. Similarly all works of detailed
anatomical research united with exact comparison and clear gene-
ralisation, are in hotany simply to be regarded as supplementary
to the little work in which Antoine de Jussieu founded the Natural
System, or in zoology to the Eigne Animal of Cuvier, himself also
an intellectual heir of Vesalius. Embryological literature in like
manner finds its place in the appendix and commentary to the
works of Eohert Brown or Von Baer respectively; at the head of
all investigations of serial homologies stands Goethe's memorable
essay On the Metamorphoses of Plants; while all evolutionary
literature may be arranged round the works of Lamarck and Darwin.
The morphological investigator, unless claiming to initiate some
new line of thought, has thus to take his place simply as an
assistant to one or more of a few immortal masters.

But the cell theory? This is apt to be excluded from general
morphology altogether, and to have a separate subordinate province
— of histology — erected for it, a vicious tendency, which although
by no means fully adopted, still somewhat injures the continuity of
treatment in the writer's recent essay on Morphology.* To ascer-
tain its position, we must first briefly glance at its history.

Here the fundamental classic is undoubtedly the Anatomie Gene-
rale of Bichat, though in this the name of cell does not even occur,
the " tissue " being assumed as fundamental. The analysis of the
organism into definite structural components is, however, the main
idea ; after this the history of histology is little more than of accumu-
lating observations with improving optical and technical appliances,
until we come to Schleiden, who boldly referred all vegetable tissues
to the cellular type, and the plant embryo to a single nucleated
cell; while Schwann, by immediately extending the generalisation
to the animal world, fully constituted the cell theory. This idea
then is fundamental in morphology; for the innumerable species
and genera of plants and animals made known under the leadership

* Eney. Brit., xvi. p. 837 ; amended in German translation, Jcnaische
Zcitschr., 1884.

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of Linnceus, and the numberless anatomical resemblances and differ-
ences investigated by Cuvier and bis disciples, become reduced to
resemblances and differences in the details of structure and position
of f undameutally similar unit masses ; while the resemblances of
development made known by embryologists become the connecting
link between the cell theory aud these generalisations of adul
structure. It is not necessary to do more than merely allude to
such applications of the cell theory, or to that of the study of patho-
logical structure initiated by Goodsir and Virchow, or to that
brilliant confirmation of the unity of the animal and vegetable cell
which has lately been afforded by the detailed study of the processes
of cell multiplication. Agassiz* was fully justified in the opinion
that the most brilliant result of modern science was the ovum-theory,
and thus it is beyond dispute that " in our own day, as in those
of Bichat and Schwann, the labours of the histologist, when inspired
by higher aims than that of the mere multiplication of descriptive
detail, are of supreme morphological importance, and result in the
demonstration of a unity of organic structure deeper even than any
which we owe to Linnaeus or Cuvier, Goethe or Geoffroy." f

Cell— The position and importance of the cell theory being thus
defined, the fundamental necessity for a precise conception of the
cell itself will be sufficiently obvious. The early progress of this is
well known ; at first the vegetable cell-wall gave the type, while
Schwann's cells were essentially nucleated vesicles with fluid con-
tents. Dujardin described the " sarcode " of Foraminifera ; Von
Mohl discovered the " protoplasm " of the vegetable cell ; while Max
Schultze identified both as the same substance; showed it, and not
the membrane to be essential ; and gave an amended definition of
the cell as a unit mass of nucleated protoplasm. Lor working
purposes it is this conception which is generally accepted, and
almost every dissertation or treatise upon the general questions of
botany or zoology, histology or physiology, commences by postulat-
ing it, the amoeba being most frequently taken as the standard type.J
Unsolved Problems. — Such a conception of the fundamental

* Essay on Classification.

t "Morphology," Ency. Brit, xvi. sec. 3, p. 840.

% (If this no better instance can be afforded than the introduction to the
admirable Manual of Physiology of Dr Michael Foster.

of Edinburgh, Session 1883-84. 269

cellular unit, however valuable, yet throws no light upon a large
number of problems at present under dispute; and it is the aim of
the present paper to draw attention to some of these, and by the
aid of a re-statement of the ceU theory (a new appendix as it were
to the Anatomie Generate, or to the work of Schwann), to propose a

solution of them.

The problems then which it is proposed to discuss may be briefly
enumerated for convenience under separate heads, as follows : —

(1) The classification and affinities of the Protozoa.

(2) The classification and affinities of the Protophytes.

(3) The systematic position of the Myxoniycetes and other
peculiar forms.

(4) The acceptance or rejection of Hseckel's third intermediate
sub-kingdom Protista.

(5) The phylogeny of the lower plants and animals, and their
origin from one or several stocks.

(6) The relation of the Protophytes to the higher plants.

(7) The relation of the Protozoa to the higher animals.

(8) The morphological relations of plants to animals and their
origin from a common stock, or from separate ones.

(9) The classification of animal tissues.

(10) The physiological rationale of changes of cell-form.

(11) A theory of the origin of sexual reproduction, and its relation
to conjugation and other cases of cell union.

(12) The relation between normal and pathological tissues.

(13) The influence of the environment on the origin of organic
forms.

(14) A theory of cellular variation (since the theory of descent
involves a theory of variation, and all variations, normal and patho-
logical alike) must ultimately be expressible in terms of cellular ones.

1. Classification and Affinities of the Protozoa. — The Protozoa
have long been thrown into a few main groups, of which the Rhizp-
poda, embracing all essentially amceboid forms like the Protoplasta,
Foraminifera, Heliozoa, and Radiolaria, and the Infusoria, including
all those of permanent and usually ciliated type, are the oldest and
most important. The position of the Gregarinida, of the Monads,
and still more of forms like Chlamydomyxa and the Labyiinthulida,

270

Proceedings of the Royal Society

or Haeckel's Protomyxa, is still disputed, nor is that of Rkizopods to
Inf usors, despite their more or less intermediate forms, as yet settled.

But our current conceptions of the groups of Protista are based
upon their more prominent and permanent characters only. An
infusorian is constantly thought of as a permanently ciliated or
flagellate organism ; a radiolarian is constantly described as a highly
differentiated rhizopod, with two layers of protoplasm, a gelatinous
envelope, yellow cells, and siliceous skeleton ; or again its simpler
ally the heliozoon is seldom or never thought of without its radiat-
ing pseudopodia with their peculiar axial filaments.

Yet such conceptions involve a morphological fallacy of the most
serious kind. These are indeed the most highly differentiated, the
most frequent, the most permanent, and therefore the most striking
forms in which these organisms are known to us, but of late years
it has been becoming more and more obvious that each of these well-
known forms is at best but the most important stage of a life-history,
during which the organism passes through one or more other phases
of form, which may indeed be transitory, but thereby lose no whit
of their morphological distinctness or importance.

Thus, thanks to the researches of Dallinger and Drysdale,
Butschli, Savile Kent, and others,* we know that a monad is not a
permanently flagellate form, but appears at one time encysted, at
another becomes amoeboid ; the ciliated embryos of the Acinette
have long been known, f while more recent investigations have estab-
lished the multiplication of radiolarians by zoopores,J or the frequent
union of several individuals of various species of Heliozoa§ or of
Gregarines|| into a single mass. In short, the progress of recent
research among these forms has largely lain in revealing the exist-
ence in even the most highly differentiated forms of a life-cycle of
several distinct phases.

In lower forms more attention is paid to the whole life-cycle, yet
not sufficiently so. The Amceba is still constantly spoken of as if
its encysted stage were of no morphological interest, whereas no
permanently amoeboid form has ever been proved by continuous

* Savile Kent, Manual of the Infusoria. + Ibid.

X Brandt, Moivxtsb. d. Berlin Akad., 1881.

§ Gruber, Zool. Anzcigcr, No. 118, 1882.

|| Gabriel, " Z. Classif. d. Gregarinen," Zool. Anzcigcr, 1880.

of Edinburgh, Session 1883-84-. 271

observation to exist; in the Gregarine, on the other hand, the
amoeboid, state is often practically ignored by classifiers.

In tho remarkable Protomyxa of Hssckel, however, we have an
organism in which several phases of form are almost equally pro-
minent, so that its description as an amoeboid, or a ciliated or as an
encysted organism, has been alike impossible. For here is no per-
manent highly differentiated form ; but an eventful life-history in
which one protean mass of protoplasm passes through a cycle of
several distinct phases. Let us carefully examine then these phases,
since light may thus be thrown upon the life-histories of the higher
Protozoa already referred to.

Starting then from the encysted stage, in which a mass of proto-
plasm is surrounded by a dense envelope, we find that from this
after a time (in which division of the protoplasm has in this case
occurred), there issues a swarm of somewhat pear-shaped, naked,
motile, flagellate organisms. After a brief period of active locomo-
tion, these lose their flagellum and their permanent form alike,
extrude pseudopodia, in short, melt down into arncebse. After
some period of amoeboid life they flow together into a single proto-
plasmic mass — unite into a plasmodium, as it is termed, and this
after another brief but remarkable period of locomotion and pseudo-
podial activity, settles down into a spheroidal mass ; this re-encysts '
itself, and the whole cycle commences anew (Plate IV. fig. 1).

If now we make a diagrammatic representation of this life-history
(or rather form-history, as it should more accurately be termed), of
Protomyxa, exhibiting (1) the encysted, (2) the ciliated, (3) the
amoeboid, and (4) the plasmodial stages, we shall find that all those
temporary phases of form observed among the higher Protozoa may
at once be referred to one or other of these (figs. 3, 8). If this be
so, those curious phenomena of the exhibition of ciliated forms by
organisms usually of amoeboid type like the Eadiolarians, or of amoe-
boid forms by organisms almost permanently encysted or motile, like
Gregarines or Monads respectively, lose their anomaly, and come
under a generalisation at once simple and comprehensive, viz.,
that a form-history essentially similar to that of Protomyxa (with
blanks it is true, but blanks which the progress of discovery is
constantly filling up, and may not unlikely almost wholly fill),
may be sketched out for all the higher Protozoa; The same idea

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Proceedings of the Royal Society

may bo better expressed in the statement that the higher Protozoa
may be regardod as organisms of fundamentally Protomyxoid form-
history, in which, however, some one phase has attained compara-
tively high specialisation and differentiation, together with relatively
greator permanence. Or the same idea may be stated in the exactly
converse way, that the Protozoa may be viewed as organisms of
fundamentally Protomyxoid form-history, in which, however, one,
two, or three of the phases become abbreviated into merely em-
bryonic ones, or may even (by that shortening of development with
which embryologists are so familiar in the higher organism) become
completely suppressed.

Thus then, if illustration be needed, a Heliozoon differs from
Protomyxa merely * in the higher differentiation and relative per-
manence of the amoeboid phase of its life-cycle, since more or less
brief encysted, ciliated, and plasmodial phases have all been observed.
The more specialised but kindred Eadiolarian seems to have lost its
plasmodial phase j so too, perhaps, has the monad, while in the
Gregarine only the ciliated state is wanting.

2. Affinities of the, Protophyta.-Pa.ssmg now to the second
problem proposed at the outset, that of the affinities of the Proto-
phytes, the same conception may be at once applied. Too much
■ importance is here attached to the encysted phase, for the life-cycle
is clearly apparent in many forms. Treviranus, in 1811, made the
notable discovery that the spores of Confervse move like Infusoria, f
Many years later linger described the same phenomena in Vaucheria
clavata, as "the plant in the moment of transition to the animal," J
while Von Siebold and others argued against this essentially just
view, with more ingenuity than soundness. The wide prevalence
of this change is constantly being confirmed. Not only have we
a thoroughly well-defined and constant cycle between the resting
and the ciliated state, but we may fairly reckon the brief phase of
inactivity, which so often is observable between the loss of cilia and
the return to the encysted state (when the organism closely resembles

* The possession or non-possession of a nucleus is of course immatcriaf, so
far as the form-history is concerned.

t Treviranus, Beitr. z. Pfi. Physiol., Gott. 1811, p. 78.

% Unger, Vic. Pflanzc in Momcnte d. Thicrwcudumj, Wiett, 1S43. Sieboid,
Dissert, de finibus int. reg. an. dreg, constit., Eriangen, 1844.

of Edinburgh, Session 1883- 84. 273

a contracted amoeba), as representing the amoeboid form. A distinct
assumption of the amoeboid state at the close of the ciliated one, is
sometimes to be observed, — as lately by Reinke* in Bangia. And
thus the cycle is complete, save only for the plasmodial phase.

The importance of this view for the Protophytes then, is scarcely
less than for the Protozoa. With a tendency of the encysted state to
predominance, more marked even than in the Gregarines, the other
phases are by no means obliterated, and we thus — and only thus —
obtain an intelligible explanation of that alternation between the
resting and the motile phase which is so frequent and so charac-
teristic. The inevitable applicability of this to classification, and
the light it yields, will be sufficiently obvious. Without prematurely
proposing a detailed classification, it will be obvious that we must
regard those forms, which like Torula, exhibit only the resting state,
not as primitive, but as exceedingly specialised, and those which
exhibit more and more of the cycle as less so.

3. Affinities of the Myxomycetes. — Passing to the Myxomycetes,
it will at once be evident, that unless the present theory can be
entirely overturned, they have no place among the fungi proper —
where it is the encysted phase that predominates, the others being
greatly reduced or suppressed ; but are in fact morphologically as
remote from these as are the monads. The Myxomycetes must be
placed next Protomyxa ; in fact, Protomyxa is simply the least
differentiated known Myxomycete. Their higher forms are interest-
ing— first, in very frequently showing less of the ciliated stage, and
secondly (a more important character, since here they are unique
among living beings), in affording an enormous differentiation of
their plasmodial stage ; the complicated forms which many of them
exhibit being simply those of their plasmodial froth, to which per-
manent shape is then given by the formation of a cellulose envelope.
The resemblance to fungi is thus as purely superficial and adaptive
as that, for instance, of Hydroids to Polyzoa, and, like it, is of physio-
logical interest alone.

4. The " Protista."— The general non-adoption of Hseckel's pro-
posal of a third intermediate Reg mm Protisticum, has been due to
three main reasons,— of which the first is that the proposal seems only
to doubly the difficulty, since it does not enable us to distinguish

* Mitthcil. d. Zool. Stat, intfcapcl., 1883.

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Proceedings of the Royal Society

Protista from animals on the one hand, or plants on the other ; the
second, closely related to the first, that Protista are too heterogeneous,
and do not admit of exact definition ; but the third and most
potent reason has, however, simply been that excessive specialisation
which allows most otherwise competent students of the Protozoa to
remain in entire indifference to the Protophytes, and the even more
general and deplorable ignorance of the Protozoa which prevails
among microscopic botanists.

The present theory, however, does away with the apparent
heterogeneity of the Protista. On the view that Protozoa and
Protophytes alike exhibit more or less specialised and abbreviated
forms of a common life-cycle, the thirteen groups of Hteckel* are
seen to be but forms of one, and there remains absolutely no
morphological reason for their continued separation (nor for that
matter, any physiological reason either, were such considerations,
irrelevant as they are to morphological taxonomy, any longer
admissible). Nor is the objection of Huxley really valid. The
limit between Protista and Animalia remains simply that between
Protozoa and Metazoa ; and that between Protozoa and Protophytes
being given up, there remains no more difficulty of separating the
higher plants than there was before— a difficulty which, however
undoubted, is not increased by unitiug the lower forms.

The thorough unity and naturalness of the Protista being thus
obvious, they naturally fall into a series corresponding to the stages
of the life-cycle. In the Schizomycetes and the Palmellacere the
resting and motile stages are almost equally prominent, while in
Gregarines, and still more in Desmids and Diatoms, and especially
Saccharomycetes, the encysted stage predominates. The Protoplasta,
Foraminifera, Heliozoa, and Eadiolaria represent of course the
predominatingly rhizopod or amoeboid stage, while the Infusoria
represent the ciliated, and the Myxomycetes, as has been said, the
plasmodial.

It may at first sight seem as if the old grouping of Protophyt. s
and Protozoa were not seriously modified, since the Protophyta
always essentially corresponded to the series of generally encysted
forms. And so far true 5 the encysted series may still be termed
Protophytes without any serious harm. But it must be clearly

* Die Protistcn.

of Edinburgh, Session 1883-84. 275

observed that there remains not one morphological type merely, to
be discriminated as Protozoa, but three — the ciliated, amoeboid, and
plasmodial, — all, indeed, physiologically analogous in exhibiting
movements (a phenomenon of which pure morphology takes abso-
lutely no cognizance), but as distinct in form from each other as from
the encysted form. The utter confusion which has too long main-
tained as to the distinction of plant and animal life is thus seen to
be due to the want of that discrimination of morphological from
physiological considerations, which is now happily nearly complete
in the study of higher organisms. In short, though the encysted
and usually non-motile cells or cell-aggregates may be conveniently
termed plants by the physiologist, and though usually non-encysted
and motile cells or cell- aggregates may similarly be grouped as
animals, — yet the morphologist, distinguishing form-history from
life-history, must recognise among the Protista four main lines of
differentiation, or four series, which may perhaps conveniently be
termed Protophyta, Rhizopoda, Ciliales, and Plasmoddales. (See
Plate IV. figs. 1-13 in first series.)

5. Phylogeny of Protista. — On this view also there is no necessity
for the assumption lately coming into view of the origin of the
Protista from several distinct stocks, or for accepting, with Bergh,*
so specialised a form as Peridinium as a type of the primeval
Protozoon, for all are naturally derivable from a simple Myxomycete
or Protomyxoid ancestor. Of course, this view by no means excludes
the possibility of the remoter and simpler Protamceboid progenitor
assumed by Hseckel.

6. Relation of the Protophytes to the Higher Plants. — Transverse
division may of course occur in the encysted, amoeboid, or ciliated
stage of the life-cycle of a cell. When this takes place chiefly in
the encysted state the tough and coherent wall holds the resultant
cell-aggregate together ; this cell-aggregate soon becomes moulded by
the force of the environment into some definite form ; and what wo
term a vegetable organism (a Metaphyte corresponding to a Meta-
zoon) is the result.

Put the cells of our multicellular plant do not lose their tendency
to cycle. Alike in linear, superficial, or solid aggregates, the cycle is

* Bergh, "D. Org. d. Cilio-flagellata," Morph. Jahrb. vii. 2; Abstract
by T. J. Parker, N. Z. Jour. o/Sci., October 1882.

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Proceedings of the Royal Society

plainly seen : and it is scarcely necessary to remind the reader of the
zoospores of a confervoid Alga, or of the similar mode of reproduc-
tion of a'n Ulva. It may be objected that here only two stages of
the cycle are present ; but a third, the amoeboid, not uncommonly
occurs, for that the brief quiescent state of the zoospore before
re-encystment may fairly be considered amoeboid, is demonstrated by
such observations as those of Keinke,* who has lately figured a true
amoeboid stage in the settling zoospore of Bangia.

In Fucus, again, the ovum- cell has rejuvenesced, in other words
has gone through an amceboid stage, while other cells rejuvenesce
as antherozoids into the cibated phase. In the terrestrial Arche-
goniata, too, we have the same phenomena; even in the Phanerogams,
condemned as all their cells seem to perpetual incarceration, there
remains one fleeting and imperfect recapitulation of the cellular life-
cycle in the embryonic rejuvenescence of the pollen grain and ovum
cell (see fig. 15).

7. Relation of Protozoa to Higher Animals. — If transverse
division occur in the ciliated state, the new cells must necessarily
almost invariably separate, must row apart, and thus it is natural
that only comparatively few and transitory cases of ciliated aggre-
gates are known. In the amceboid state, however, the aggregate
produced by division remains much more readily in continuity, and
it would thus seem much more probable that the Metazoa should
originate from Protista in which the amceboid stage was somewhat
more permanent and more subject to division, than from the ciliated
forms, as has sometimes been suggested, particularly for the sponges.

8. Common or separate Descent and Affinities of Animalia mid
Vegetabilia. — If the preceding facts and deductions be accepted, it
need only be briefly pointed out, that the affinities of plants and
animals are far closer than botanists and zoologists are generally
accustomed to assume, since both are descended from a Protomyxoid
ancestor, and may, in fact, from our present point of view, be
described not merely, as the common phrase goes, as amoeboid or
encysted cell-aggregates, but as aggregates of Protomyxomycetes,
variously grouped and arranged indeed, but never so highly spe-
cialised as to lose all traces of their individual ancestral life-cycle.
The notion of three kingdoms of nature— animal, vegetable, and

* Op. cit.

of Edinburgh, Session 1883-84. 277

mineral — " that disastrous philosophic and scientific aberration "
bequeathed by the alchemists to the last cncyclopeedist of Gesner's
school, and unfortunately adopted and sanctioned by Linnaeus, has
not of course been seriously adopted by any philosophical biologist
of the century ; hardly the narrowest specialist among zoologists or
botanists any longer seriously doubts the validity of the classifica-
tion of natural objects into two groups only — inorganic and organic —
yet, at the same time, the vicious results of the earlier dogma still
everywhere survive, and indeed necessarily so. For the unity of
plant and animal life requires morphological demonstration, and that
more precise than has hitherto been afforded by merely separating
off the lowest plants and animals into a third still heterogeneous
group of Protista. This deficiency is supplied by the present argu-
ment, for if the Protista, the Vegetabilia and the Animalia have
indeed been correctly interpreted, as somewhat variously specialised
cell-aggregates derived from an ancestral Protomyxomycete, their con-
solidation into a single kingdom is a matter of course. In one edition
of the Systema Naturce, Linnseus clearly recognised the fundamental
unity of plants and animals, by uniting them in opposition to the
non-liviug world (Conserta) as Organisata, and this term it is accord-
ingly not only convenient but necessary forthwith to revive.

9. Morphological Classification of Animal Tissues. — Histologists
are accustomed to recognise three main groups of animal tissues.
Thus Cornil and Eanvier* distinguish (1) connective tissues, in
which the cells are united and separated by a substance of charac-
teristic form and properties; (2) muscular and nervous tissue, in
which the cells have undergone extraordinary modifications, both
structural and functional; (3) epithelial tissue, in which the cells
possess a regular and constant evolution.

In this classification, however, as in so many others, morphological
and physiological characters are not kept distinct. In briefly
glancing at morphological characters only, it is evident we may best
approach the problem by first noticing some of those cellular trans-
formations made known by the recent students of embryology.
Histogenesis must underlie histology.

An ovum is at first a naked amoeboid cell, then assumes the

encysted state, then segments into an aggregate of amoeboid cells ; this

* Manuel cV Histologic Pathologiquc, i. p. 11, Paris, 1881.
VOL. XII. T

278 Proceedings of the Royal Society

becomes perhaps a ciliated morula, this again a gastrula, with ciliated
ectoderm and amoeboid endoderm ; this may settle down as in sponges,
its cells re-cycling anew, the ectodermic layer becoming amoeboid,
the endodermic ciliated (fig. 18). The endodermic cells remain per-
manently more or less amoeboid, as the recently much investigated
phenomena of intercellular digestion have so clearly established.
The amoeboid ectodermic cells, on the other hand, may give rise to
muscle — and a muscle is but an amoeba elongated so as permanently
to contract along one line ; on the other hand, they may pass into
a quiescent state, or throw out encysting material, which may either
enclose them individually, as in Ascidians, or form a collective
external envelope, as in Arthropods. The mesodermic cells may
either remain unspecialised as amoeboid corpuscles, may specialise as
muscular tissue, or cycle into the resting state, i.e., develop into
connective tissue (see fig. 19).

And if the cell cycle persist thus long in the life-history of the
organisms, why should it disappear? In reality, it does not
disappear completely. The amoeboid corpuscles of the perivisceral
fluid of an invertebrate — say an Echinus— develop, largely at least,
from the ciliated epithelium lining of the ccelome — permanently
exhibit, that is to say, one of the most characteristic phenomena
of the cycle. And when under proper precautions we examine
a fresh drop of the fluid, we observe the corpuscles as they die
running together into a plasmodium,* so perfectly similar to that
of a Myxomycete as actually to have been described by a recent
observer as a new genus and species, f And this phase of the cycle
takes place, in the so-called Coagulation of corpusculate fluids of inver-
tebrates generally.:]: Numerous other instances of the occurrence of
some phase of the cell-cycle have been recorded, and have already
been collected by the writer in a series of papers which have led to
the present one ; it is unnecessary to call attention to others, save
perhaps the especially interesting announcement by Professor Had-
don,§ of the occurrence of a plasmodial union of cells during the
normal histolysis of Polyzoa.

* Geddes, "Observations s. 1. fluide perivisceral des Oursins," Arch. Zool.
Exp. VIII. + Comptcs Rcndus, t. lxxxii. No. 21.

•j- Geddes, " On the Coag. of Amoeb. Cells into Plasmodia," &c., Proc. Boy.
Soc. Lond.,'^o. 202, 1880, and Trans. Roy. Phys. Soc. Edin., 1S82.
§ Haddon, " On Budding in Polyzoa," Quart. Jour. Micros. Sci., 1883.

of Edinburgh, Session 1883-84.

279

Thus then it will be sufficiently evident that the morphological
classification of tissues must be based upon the cell-cycle, the various
permanent tissues being viewed as specialisations of one or other of
its fundamental forms, or perhaps sometimes as synthetic types
between them. And, finally, compressing the gist of several possible
papers into as many passing allusions, it is evident that the theory
affords us a basis for the criticism and compression of the recent
literature — (1) of intercellular digestion (natural to the amoeboid
phase); (2) of that long dispute respecting the origin of the sexual
elements of Hydrozoa, from ectoderm to endoderm (the cells of both
of which show the cycle, and either layer thus develop ova or sper-
matozoa) ; (3) of the ccelome theory.

10. Physiological Rationale of the Cell-Cycle. — It is now time to
demand some physiological rationale for this cycle, which has been
hitherto -regarded as of morphological interest alone. A mass of
protoplasm anywhere is under constantly varying conditions — at
one time receiving abundant energy from the environment, at
another little or none. These variations are at least of three main
kinds— (1) temperature, (2) light, (3) food. Thus, then a rhythm
of more or less vital activity in definite relation to these conditions
of the environment is inevitable.

It is unnecessary to remind the histological reader how often and
how easily the existence of this rhythm is verified by actual obser-
vation. Every student is shown the intensification of amoeboid or
ciliary movement by heat, and its depression by cold or electric
shock, and knows too the influences of various reagents or cases
(i.e., of modification of food in the general sense) in stimulating or
retarding activity. The dependence on climate of the cell-cycle of
the lower organisms, e.g., Protococcm or Amoeba, is familiar to every
microscopist. The amoeboid state varies widely with food and
temperature ; while the actual transition from the ciliated stage to
the amoeboid, and conversely, have been repeatedly observed ;
witness the papers of Haeckel, Lankester, and others including the
writer* They can only be viewed in fact as distinct from the
morphological point of view ; physiologically, they show but the
extremes of one motile state.

* "On the Morphology and Physiol, of the Cell," Trans, Roy. Phm. Soc.
Min., 1882.

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Vast importance has been attached to the cellulose wall, as an
assumed characteristic of plants, yet not only the cyst of a Myxo-
mycete, but that of an Amoeba, is now known to consist of cellulose.
How is this cellulose wall to be accounted for1? Why should the
resting phase possess a cyst ? What is the physiological rationale
of this morphological characteristic of the resting phase 1

Contracting muscle evolves carbonic acid and water, with evolu-
tion of heat; the quantity of heat and water products evolved
diminishes as contractile activity diminishes ; and this physiological
common-place must hold true of every contracting cell, ciliated or
amoeboid. But contractility implies waste of formed materials,
diminution of contractility therefore implies diminution of this dis-
integration of matter and dissipation of energy, of this combustion
which we term waste. Cessation of contractility, therefore, involves
cessation of the combustion of some product— of some fuel which
was formerly required to maintain the process. The cellulose
wall which appears on the assumption of the quiescent state is thus
the equivalent of the carbonic acid and ivater which were being
formed and excreted during the state of contraction. Being no
longer required as fuel, it becomes itself thrown out as a waste pro-
duct—which simply by reason of its chemical and physical proper-
ties its insolubility and coherence— acquires at once its morpho-
logical permanence and its protective use.*

°The applicability of this physiological conception to a new series
of problems can here only be briefly hinted at. Without more than
mentioning the discovery of Burin as to the formation of cellulose
from cane sugar,t it may be briefly pointed out (1) that the occurrence
of cellulose in Ascidians, or in pathological cases in the human brain,
&c , is by no means unintelligible-the difficulty is rather the
reverse-to explain why it is not invariably present in resting cells.
These are never destitute of external intercellular substance, and the

* A vivid confirmation of the preceding theory of the origin of the cellulose
wall h « been suggested to me since the reading of this paper by my friend l)i
JSC who reminds me that a quiescent muscle, instead of evolving
Milne Murray , w enormous store of muscle-sugar or inosite,

"fX 5! i an 'so of cellulose, O,H10O,. The same conception may

glycogen, starch, &c

f Ann. Sci. Nat. Bat., 1877.

of Edinburgh, Session 1883-81.

281

hypothesis thrown out many years ago by M. FriSiny, our leading
authority upon the chemistry of cellulose — that chitin and other
analogous bodies really consist of cellulose linked with a proteid,
seems well worth reviving. On this point the researches of Kruken-
berg,* especially are promising light, f

11. Origin of the process of Sexual Reproduction. — The plasmodial
stage which terminates the cycle, seems in the first place little more
than a mere mechanical union of cells exhausted by prolonged
activity ; in all normal cases it is soon followed by prolonged repose
in the encysted state, and in the experiment upon invertebrate cor-
puscles, by quiescence and death. In the plasmodia of Protomyxa,
Myxomycetes, and of invertebrate corpuscles alike, notably Echinus,
the union is followed by a brief but extraordinary intensification of
amoeboid activity % — the cause of which, as passing from cellular to
protoplasmic physiology, must be discussed in a subsequent paper.

Some years ago considerable weight was attached by Sachs § to
the hypothesis that the plasmodium formation of Myxomycetes might
be regarded as a process of multiple conjugation. This view he now,
however, withdraws, || mainly on the ground that the nuclei have
been shown not to coalesce as in true conjugation. It appears to
me, however, that on the present theory the revival of that hypo-
thesis, though in a somewhat different form, is inevitable.

one doubts that the sexual elements of plants and animals are
represented by the very slightly differentiated conjugating cells
of Spirogyra, or the almost undifferentiated cells of Mesocarjpus.
With these the conjugation of two Amoebee, two Actinosphasria or
two Gregarines, are classified as a matter of course. But the recent
observations of Gabriel upon the multiple conjugation of Actino-
sphteria, or of Gruber upon that of Gregarines, leave no doubt that
in these cases at least conjugation may be multiple. The only
difficulty is that offered by the non-coalescence of the nuclei. But
even if there were any certain grounds for supposing that the
essence of the process lies in the union of the nuclei, rather than in

* Krukenberg, Verglcich. Physiol. Studicn, Bd. ii.
\ Ann. Sci. Nat. Bot., 1877.

t See figure of plasmodium of Echinus in author's papers in Arclx, Zool.
Exp. VIII.; Proc. Roy. Soc. Lond., 1880, or Trans. Roy. Phys. Soc. Edin.,l&$2.
§ Manual of Botany, 1st Eng. ed.
11 Ibid., 2nd ed., Appendix.

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Proceedings of the Royal Society

the union of the protoplasm, we must expect on the evolution theory
an incipient stage in which only the latter phenomenon should
occur. That the nucleus is not invariable, much less indispensable,
is of course evidenced by the existence of the Monera, or if their dis-
tinctness be questioned, we may appeal to the recent demonstration,
apparently by the most refined histological appliances, that in young
Actinophrys a nucleus is really absent,* and develops independently
in adult life. Moreover, on the present view of the almost primordial
nature of the Myxomycetes, their plasmodium is the only phenomenon
which at all resembles conjugation, and since we have already viewed
amoeboid, ciliated, and resting forms as specialisations of the cor-
responding phases, it is no great extension of the theory to view
conjugation as specialised from the plasmodial phase. This view
will be strengthened when in the next paper we leave the cell-cycle
to consider the physiological processes in the protoplasm itself.

12. Relation between Normal and Pathological Tissues. — Unless
the step taken by Goodsir and Virchow— of regarding all patho-
logical variations as ultimately expressible in terms of cellular
structure and function, i.e., of the cell theory, be deliberately re-
traced, we cannot avoid the application of the present re-statement of
the cell theory to pathology, To do this in detail would, of course,
require far more than the writer's knowledge, but a few brief and
tentative suggestions may be put forward. Pathologists are reducing
tumours to a common type — which seems essentially that of cell
multiplication in the resting or encysted stage. It is certainly more
easy to suppose, on the present view, that the appearance of a con-
nective tissue tumour has been due to the placing of ordinary cells
in new conditions favourable to the assumption of that phase of the
ancestral cycle ; or from a slightly different point of view, to say that
that inhibition of the cycle essential to the permanence of the whole
organism has been locally removed, than, for instance, to suppose, with
Cohnheim, the existence of a long dormant mass of embryonic tissue.

Again, we can easily modify the environment of living cells under
the microscope — we can accelerate or diminish the activities of
ciliated epithelium, by heat and cold, oxygen and carbonic acid,
by alkali and chloroform. I have elsewhere f pointed out that the

* Gruber, Zool. Anzcigcr, No. 118, 1882.
t Op. cit., Proc. Roy. Soc. Lond., 1879.

of Edinburgh, Session 1883-84. 283

solution of the old dispute, as to whether the integument of certain
planarians was amoeboid or ciliated, was afforded by specimens of
Convoluta which had been kept for many days in a shallow aquarium,
scantily protected at nights from the cold of a severe winter.
The normally ciliated cells of the ectoderm could be watched in
actual progress of collapse into the amoeboid state, and their cilia
figured during their passage into pseudopodia (fig. 24). Here was
a definite pathological change, in approximately known conditions,
and distinctly in terms of the cell-cycle. Why should not a dis-
order of the ciliated epithelium of the bronchial passages be at least
partly susceptible of essentially the same explanation? (fig. 25).
May not the formation of pus be partly interpreted in terms of
degeneration to the amoeboid stage, and may not inflammatory
changes be regarded as temporary and excessive intensifications of
cellular activity, indicating a tendency to reversion to the amoeboid
state ?

Whether these particular instances be acceptable to professed
pathologists or not is after all a minor consideration, their aim has
been merely to suggest that the phenomena of the cell-cycle —
and particularly of those changes occurring under definite experi-
mental conditions — may be applicable in their hands to fruitful
research, not only in pathological histology, but in cellular physi-
ology and therapeutics.*

Its adaptability to the treatment of physiological speculations is
also obvious. Since the activities of the body are the aggregate
activities of its component cells, not merely such phenomena as
those of varying ciliary activity, but those of fatigue and sleep,
of muscular and nervous tonus, and in fact every rhythm of increas-
ing and decreasing cellular activity, become intelligible when viewed
from this most highly generalised standpoint of physiology, as
specialisations of that primeval cellular rhythm which lies before us
in this life-history of the Protomyxomycete.

13. Influence of the Environment upon the origin of Plants and
Animals. — One further physiological consideration may be briefly
indicated, from its bearing on general morphology. The cell-cycle
in its entirety is only possible in a fluid medium. Without water
cilia cannot play, without fluid the amoeba and the plasmodium must
* This conception is somewhat developed in the subsequent paper.

284

Proceedings of the Royal Society

alike become stationary, and either dry up or encyst themselves.
The cell-cycle in plants therefore is only found in its entirety in
algaj. Archegoniates are indeed terrestrial, but their brief cell-cycle
during fertilisation is absolutely dependent upon the abundant
moisture, without access to which neither moss, liverwort, nor pro-
thallium ever occurs. Thus it is that the higher terrestrial plants
have become restricted to the encysted phase. Only to escape death,
has the dryad become thus shut up within the tree ; but once so
protected the extensive replacement of the cryptogams by the
phanerogams, in all the less humid climates of the world, is readily
accounted for.

Passing to animal life, the vast preponderance of aquatic forms
over terrestrial, is very similarly to be accounted for by the aid of
the present theory. Only the higher members of a few groups have
successfully emerged from their native element, and their existence
depends upon their differentiation of an internal fluid medium, of that
" milieu interieur" upon which Claude Bernard was wont to lay such
stress,* this in turn depending upon the early differentiation of in-
ternal cavities. The interdependence of morphological and physio-
logical theory will be sufficiently obvious from such considerations.!

14. Theory of Variation. — The more completely one accepts and
reflects upon the theory of natural selection, the more one feels the
necessity for some view more satisfactory than heretofore of the
causes of variation. % The present conception of the cell-cycle seems
to go far towards supplying this. On the ordinary conception of
the cell theory, that of the plant as an aggregate of encysted cells,
and of the animal as an aggregate of essentially amoeboid ones, the
organism cannot be credited with any innate variability— its ob-
served variations are merely those which it receives, so to speak,
between hammer and anvil— from the forces of the environment.
The present conception, however, of all cells, however varied and
specialised, being essentially differentiations from an encysted, an
amoeboid or a ciliated form, and of these forms as phases of a
single form-history, enables us to credit the cells and the resultant
organism with an innate tendency to variation, and this along

* PMnomencs dc la vie communs aux an. et auxvig., Paris, 1879.
+ " Morphology," Ency. Brit., 'Eel. of Morphol. to Physiol. '
X Cf. Or igin of Species.

of Edinburgh, Session 1883-84. 28o

certain definite and investigable lines. These modifications would
still of course be largely determined by modification in the environ-
ment, yet the change of view is considerable. On the former view
the organism is a plastic but essentially inert mass, yielding pas-
sively to the forces of the environment ; on the latter, it is an active
community, of which some or many members, under the influence
of any favourable change of conditions, or the removal of any
restraints, external or internal, immediately press into other positions
and functions, which however apparently new, are either specialisa-
tions of the existing, or reversions to an earlier type.

Variation and disease are thus most closely akin ; for since all
variations are ultimately cellular, pathological changes are simply
definable as those variations which happen not to be conducive to
success in the struggle for existence. And thus we might proceed
further and further with the discussion of aetiology.

The preceding theory then, although its range of application, un-
limited in the scale of organic nature, may at first sight alarm the
specialist, is actually founded on a simple but solid basis of observed
facts; it has been seen fairly to meet and co-ordinate the very
numerous and hitherto, for the most part quite unrelated problems
which were enumerated at the outset, and even to be applicable to
numerous minor and unexpected problems which these suggested.
And thus, were it even viewed from the standpoint of mathematical
probability alone, it has received the most overwhelming verification.
(Explanation of the Plate at page 292. )

II. An Hypothesis of Cell Structure.

1. Statement of the Froblem. — -Great attention has, especially of
recent years, been paid to the problem of cell structure, and a vast
body of observations have been accumulated. Of these many are
generalised ; many, however, still remain unco-ordinatecl, and an
hypothesis which attempts at once to unify these, to throw light
upon the structural and functional aspects of contractile protoplasm,
and to unite all these with that theory of the cell-cycle above pro-
pounded, is therefore not untimely, and may, even if not completely
exhaustive or satisfactory, be at least suggestive of a better explana-
tion. Let us survey a few of the main peculiarities of protoplasmic
structure which any such hypothesis must aim at unifying.

286 Proceedings of the Royal Society

The lowest amoeboid organisms are simply granular masses of
protoplasm, but higher forms exhibit a differentiation of a hyaline
zone of "ectoplasm" around a more fluid and granular "endoplasm."
The immense variability of form, size, and general appearance pre-
sent among the rhizopods has never been sufficiently allowed for ;
so that there is ample reason for doubting whether great numbers of
described species have any real distinctness. Yet the elongated
and reticulated, granular and circulating pseudopodia of the Fora-
minifera, and the radiating, clear, and far less contractile pseudo-
podia of the Heliozoa and Eadiolaria present a most vivid contrast,
which we have as yet no means of explaining. The remarkable
changes presented ,by ova both before and during fertilisation,*
and the doubtless fundamentally similar phenomena exhibited
during cell division, require to be accounted for; while the long
dispute as to whether the " granules " of protoplasm are really
granules at all, or are the optical expression of the intersections of a
stroma or network of denser protoplasm, cannot be omitted. Such
a hypothesis must also aim at throwing light upon the mystery of
muscular structure, and must also deal even -with such apparently
peculiar and exceptional phenomena as that "aggregation of the proto-
plasm," first described by Mr Darwin as occurring in certain cells of
insectivorous plants f (which, when in active digestion, or when
subjected to chemical, electrical, or even mechanical stimuli, exhibit
an aggregation, or rather segregation of the protoplasm into two
portions — the outer more or less hyaline, but containing irregular
and constantly-changing streaks and granules of a more refracting
and fluid substance, in which the colouring matter, when present,
became accumulated).

2. Statement of the Hypothesis. — Darwin soon extended these
observations to the protoplasm of root hairs, and went on to indicate
its wide prevalence throughout the vegetable kingdom. His re-
searches were verified and extended by Francis Darwin,;}: who
showed that these granules did not consist of sap, as some vegetable
histologists had suggested, but were essentially protoplasmic in their
nature. It is the object of the present paper to apply these facts to

* Balfour, Embryology, vol. i.

t Darwin, Insectivorous Plants, London, 1S75.

X Quart. Jour. Micros. Science, xvi.

of Edinburgh, Session 1883-84. 287

the explanation of such problems of cell structure and contractility
as those briefly enumerated above.

On this view, the granules of such a low vegetable organism as
Torula (disregarding, of course, sap vacuoles and fat globules) are
aggregation products, an assumption by no means excessive, espe-
cially when we bear in mind the activity of the chemical changes
•which are going on during its life and growth. But if this step be
taken, we cannot resist regarding the Amoeba in the same way ; its
granules too are aggregation products, and the clear ectoplasm,
when present, may be viewed as protoplasm in which aggregation is
not occurring. The variations of amoeboid organisms in more or
less granular character (a fact familiar to every observer) is thus
brought into obvious relation with the state of nutrition, or with the
quality and quantity of external stimuli ; and its observed increase
when stimulated, and its diminution during the resting state, are
thus naturally accounted for. In the same way, in the granular
pseudopodia of the Eoraminifera, aggregation is in progress, in the
hyaline processes of the Heliozoon not so. The granules of cells in
higher animals may be, at least to a very large extent, similarly
explained ; while the disputes as to the presence or absence of a
stroma become clearer when we bear in mind the fact that Darwin's
aggregation-masses are at least as often greatly elongated or spherical,
and that they may run in any direction, and unite or separate to any
extent. The remarkable differentiations of protoplasm visible during
cell-division, as exhibited by ova (of course excluding yolk granules,
&c), may not improbably admit of the same explanation.

3. Contractile Structures — Muscle. — The excessively difficult
problem of muscular structure has not as yet received any widely-
accepted solution, and even respecting matters of observation the
widest discrepancies exist. In many invertebrates we cannot even
be certain whether the muscles are striped or non-striped, so contra-
dictory are the observations, while in a recent important paper by
Professor Haycraf t,* the homogeneity even of striated muscle is main-
tained. Brilliant light has, however, been lately thrown upon
the arena of controversy by Professor Kuthcrford's recent elaborate
demonstration f that the discrepancies in observation arc largely

* Proc. Roy. Soc. Lond., 1881.
t Proc. Roy. Soc. Edin., 1883.

288

Proceedings of the Royal Society

if not indeed altogether, to be explained by the fact that the
different observers have studied their specimens in different stages
of contraction. When fully extended, and then alone, the full com-
plexity of the structure of striped muscle can be realised; with
slight contraction Flogel's granules disappear, then Dobie's globules;
finally, in completed contraction, the heads of adjacent sarcous
elements come together, and the fibril is momentarily homogeneous,
the former complexity reappearing on extension. So far Professor
Eutherford's explanation — how does this come into relation with
the present hypothesis? The doubly refracting portions of the
muscle-fibrils may, on this view, be regarded as aggregation granules ;
for these must inevitably exhibit considerable regularity of form
and arrangement, when we bear in mind that, if we admit the exist-
ence of muscle-fibrils at all, we imply that these possess a limiting
surface, — of course tubular in form and ultra-capillary in fineness, —
and still more so, if we assume with many histologists the existence
of fixed points afforded by Krause's membrane.* In short, it is
attempted to compare the aggregation-granules of a sundew, not only
with those of an amoeba, but even with those most complex and most
peculiar differentiations of protoplasm observable in muscular tissue.

4. Confirmatory Evidence. — The present hypothesis is thoroughly
in accordance with recent researches as to the nature and composi-
tion of protoplasm. Thus Brass f distinguishes cells into two
layerSj — the outer sensory, the inner nutritive, and describes
phenomena which seem at least closely akin to aggregation.

Our knowledge of the development of muscle also supports the
hypothesis. Thus, for instance, Wagener $ shows that muscular fibres
at first differentiate from the protoplasm of multinucleate cells, as
perfectly smooth fibrils ("vollig glatte laden"), with interfibrillar
substance. Later there arises, as a secondary differentiation, the
refracting and non-refracting elements (" Isotropen and Anisotro-
pen"), which can extend and diminish, also fuse together and again
separate. In young heart-muscles these come and go under the
observer's eye.

* Cf. Author's Prol. Note in Zool. Anzeigcr, No. 146, 1S83.
t Brass, Zool. Anzeigcr, 120, 1882.

% G. Wagener, " Ueb. d. Entstcliuug. d. Querstreifen auf d. Muskeln,"
Archivf. Anat. u. Physiol, Anat. Abthcil, p. 543.

of Edinburgh, Session 1883-84. 289

5. Further Study of Aggregation— Cellular Therapeutics.— High
as is the importance of observations upon preserved tissues, the
present hypothesis clearly points towards the importance of con-
tinuous observation of living cells when treated with various re-
agents—aline of research which Professor Frommann* is at present
almost alone developing, and with such remarkable results. We
must observe the effects, not of amnionic carbonate only, but of
the whole pharmacopoeia, and not upon the tentacles of Drosera
merely, but upon vegetable and animal cells and tissues from the
lowest to the highest ; noting the changes which take place in all the
structures and functions of the cell, and this, under all variations of
temperature, light, electric state, and for various periods of time.

Of the practicability and interest of such an investigation only a
single instance need be taken. When one treats an Actinosplia:rium
with dilute ammonic carbonate, the most striking change results; its
pseudopodia disappear, its complex protoplasmic structure vanishes;
it loses its regular spherical shape, and collapses into an irregu-
o-ular granular amoeboid mass with blunt pseudopodia— (the very
likeness of the ancestral amoeba),— and then soon breaks up.

And similarly there is little doubt that such a reagent would pro-
duce marked effect upon the epidermic cells of growing tadpoles,— a
convenient means of research; Thus we set out from these re-
searches of Mr Darwin upon a general investigation into what
changes chemical substances produce upon cells, — an investigation
which touches the general question of pharmacy and therapeutics in
the most direct way, and which we may in fact speak of as cellular
therapeutics. The interest of the admission of a drug does not
end when it has been conveyed into the stomach, but really begins
there. We must know what happens to the component cells of the
organism, — we must, in short, observe the therapeutic effects of
reagents upon the cells of vertebrates, — an investigation which points
far. Such observations would not require constant but only frequent
attention for long periods, and are thus perhaps especially suitable
for the skilled pharmacist, f

* Frommann, " Untersuch. ueb. Struktur, Lebenseracheinungerj u. React-
tionen thier. u. pflanz. Zelleii," Jena Zeitschr., xvii. and Sep. put)., Jeua,
1884.

t Cf. Author's paper in Jour. Pharmaceutical Soc. Lond., No. 714, 1S84.

290 Proceedings of the Royal Society

6. Further Chemical Considerations. — It is an observed fact that
when ainceboid cells unite into a plasmodium, there takes place the
most remarkable intensification of the activities of the mass. The
compound amoeba seem possessed of all and more than all the
activities of its component amoeba — pseudopodia of the most extra-
ordinary length and size are thrown out, and motion is far more
rapid ; in short, it would seem that not only are the activities of the
component amoeba summed but multiplied. The coalescing amoebae
majr be regarded as serving as food to one another — their waste pro-
ducts and their surplus water are squeezed out and got rid of, and
thus we can readily understand the summation of their activities.
But how is this apparent multiplication of activity to be explained ?

We have seen how carbonate of ammonia, an oxidised body
isomeric with urea, is exceedingly stimulating to protoplasm; and
Mr Darwin's researches have also shown that other alkaloids and
waste products are excessively stimulating, and set up the most
extraordinary aggregation ; and that a poison, for instance, may act
by excessively exaggerating this normal process. Here then is a
use, not merely for the protoplasm, but actually for the waste pro-
ducts— the waste product of one cell acting as a stimulant when it
meets the protoplasm of another. And from this consideration
again new series of speculative applications radiate off in all direc-
tions. One may suggest that the use of the alkaloids in the coffee
or strychnine or Calabar bean is not merely to protect the young
embryo from being eaten by animals, but as a stimulant to germina
tion. Or we may introduce the same conception into our specula-
tions as to the uses of manures, in which the most valued consti-
tuents are precisely those salts which, like carbonate of ammonia,
produce great aggregation.

Again, passing from the plasmodial union of cells to the probably
derived union of ovum and spermatozoon, we cannot avoid imagining
tbe latter bringing not merely a trifling contribution of additional
protoplasm, but a store of substances especially stimulating to the
vast mass of the ovum. And the identification above suggested
of aggregation with the protoplasmic changes visible in the ovum
after fertilisation, is thus seen to be by no means so improbable as
might at first appear.

7. Need of an Explanation of the Phenomena of Aggregation. —

uf Edinburgh, Session 1883-84 291

How is it that if we treat living protoplasm with certain reagents it
breaks up into two substances? How are we to explain this
observed fact ? Is there any case known to chemists or physicists
where a chemical reagent separates a substance, at first apparently
homogeneous, into two distinct substances which afterwards reunite ;
or where an electrical or mechanical stimulus temporarily separates
a complex mixture into its components 1 I am not aware of any
parallel case; but the absence of an explanation underlying the
phenomenon of aggregation itself is after all entirely outside, and
subsequent to both the main thesis and the speculative corollaries
of the present paper.

III. An Hypothesis op Contractility.

If we imagine a single drop of more or less fluid substance sus-
pended in a surrounding medium with which it does not mix, its
surface-tensions tend to keep it in a spherical form. This can of
course be observed in a drop of oil or water, most conveniently in
the well-known experiment in which oil is suspended in a mixture
of alcohol and water of the same specific gravity. If now we
interfere and elongate this drop, its surface tensions at once enable
it to resume the spherical form, even against the resistance of the
surrounding medium. It is inevitable to transfer this simple
physical conception to explain the function of muscle. If the
elongated components of the muscular fibre be more or less fluid
(as we almost certainly know them to be, whether aggregation
granules or not), they must needs also possess surface tensions;
they must, therefore, also tend to shorten and broaden, and draw
themselves into a sphere. And if all these multitudinous elements
of the muscle are shortening and broadening, we have of course an
explanation of that general shortening and broadening which we
term the contraction of a muscle.

Moreover, just as the " contracting " drop of oil overcomes a
resistance, so the "contracting" muscle overcomes a resistance equal
to the sum of the minute resistances which the millions or thou-
sands of millions of simultaneously contracting elements can over-
come. Finally, an expenditure of energy must needs take place,
and of this the " negative variation" of contracting muscle (perhaps
of the contracting oil-drop also 1) may afford the indication.

292

Proceedings of the Iioyal Society

Be the latter suggestion valid or not, it is important to observe
(1) that we Lave here (and for the first time so far as the writer is
aware) an hypothesis which explains (a) the shortening and broad-
ening of a contracting muscle, (b) its overcoming a mass resistance,
in other words, that we have an explanation of the mode in which
almost molecular movements are converted into movements of
masses, a solution long sought by physiologists ; and (2), that this
hypothesis depends simply upon the more or less fluid nature of the
essential muscular components, and is entirely independent of the
acceptance or rejection of the hypothesis of the preceding paper,
which suggests the identification of these muscular components with
aggregation granules.

Explanation of Plate IV.

In columns allotted to the four stages of the cell-cycle (encysted, cili-
ated, amoeboid, and plasmbdial) are arranged the corresponding phases
of the form-history of a few typical Protozoa and Protophytes, as also a
series of diagrams illustrating the normal and pathological form-history
of the cells of higher plants and animals. All are thus seen to be refer-
able to the Protomyxan or Myxomycete type.

Among the Protozoa proper (figs. 3-8) the cell-cycle is almost com-
plete ; the encysted and amoeboid stages are invariably represented. The
plasmodial phase is of frequent occurrence : in Infusorians, Gregarines,
and Heliozoa that of multiple conjugation representing it, and demon-
strating its essential continuity with conjugation, e.g., diatoms and alga}
(figs. 10-13), and even with fertilisation in plants and animals (figs.
14 and 16).

Fig. 18 shows the cell-cycle in a developing gastrula, e.g., sponge. In
fig 19 the various tissues are classified in relation to the cell-cycle ; the
connective tissues to the encysted, the muscular to the amoeboid type, &c,
even the plasmodial phase being represented during the histolysis of
Polyzoa Fie 19 represents the development of an invertebrate amoeboid
corpuscle, and fig. 20 its formation of a plasmodium when draw,
while figs. 20-25 continue the application of the same theory to the
explanation of pathological change.

Proc. Hoy. Soc. JSdm1., VoJ.All, mte