CYSTOLITH-CYTISINE

6. Noctiluca miliaris, acted upon by iodine solution, showing the protoplasm shrunk away from the structureless pellicle.

a=entrance to atrium.

7. Lateral view of Noctiluca miliaris.

a, entrance to atrium.
b, atrium.

c, superficial ridge.
d, big flagellum.
e=mouth and gullet, in
which is seen Krohn's
oral flagellum (=the
chief flagellum, Or
flagellum of the longi-
tudinal groove of Dino-
flagellata).

broad process of proto-
plasm extending from
the superficial ridge c
to the central proto-
plasm.

g, duplicature of pellicle in
connexion with super-
ficial ridge.

h, nucleus.

conjugation between two adults takes place by their. fusion commencing at the oral region; flagella and pharynx disappear and the nuclei fuse, while the cytoplasts condense into a sphere. The nucleus undergoes broad division, the young nuclei pass to the surface, which becomes imperfectly divided by grooves into as many rounded prominences as there are nuclei (up to 128 or 256); and these become constricted off from the residual useless cytoplasm as zoospores with two unequal flagella, which were at first regarded as Dinoflagellates, of which they have

been observed.
the form (figs. 5, 6). The metamorphosis of these has not yet

LITERATURE.-E. Suriray, Magazin de zoologie, 1836; G. J.
Allman, Quarterly Journal of Microscopic Science, n.s. xii., 1872;
L. Cienkowsky," Zoospore formation in Noctiluca," Archiv f. mikro-
skopische Anatomie, vii., 1871; R. Hertwig," Leptodiscus," Jenaische
Zeitschrift, xi., 1877; C. Ischikawa, Journal of the College of Science
Zoologische Jahrbücher, Anatomie, xiv., 1900; C. A. Kofoid," Craspe-
dotella," in Bull. Mus. Comp. Zool. Harvard, xlvi., 1905; O. Bütschli,
(M. HA.)
(Tokyo, 1894), xii., 1899; F. Doflein, "Conjugation of Noctiluca,"
"Mastigophora," in Protozoa (Braun's Thierreich, vol. i., Protozoa)
(1883-1887).

CYSTOLITH (Gr. KUOTIS, cavity, and Milos, stone), a botanical
term for the inorganic concretions, usually of calcium carbonate,
formed in a cellulose matrix in special cells, generally in the
leaf of plants of certain families, e. g. Ficus elastica, the india-
rubber plant.

CYTHERA (mod. Cerigo, but still officially known as Cythera), one of the Ionian islands, situated not less than 150 m. from Zante, but only about 8 m. from Cape Malea on the southern coast of Greece. Its length from N. to S. is nearly 20 m., and its greatest breadth about 12; its area is 114 sq. m. The surface is rocky and broken, but streams abound, and there are various parts of considerable fertility. Two caves, of imposing dimensions, and adorned with stalactites of great beauty, are the most notable among its natural peculiarities; one is situated at the seaward end of the glen of the Mylopotamus, and the other, named Santa Sophia, about two hours' ride from Capsali (Kapsali). Less of the ground is cultivated and more of it is in pasture land than in any other of the seven islands. Some wine and corn are produced, and the quality of the olive oil is good. The honey is still highly prized, as it was in remote antiquity; and a considerable quantity of cheese is manufactured from the milk of the goat. Salt, flax, cotton and currants are also mentioned among the produce. The people are industrious, and many of them seek employment as labourers in the Morea and Asia Minor. Owing to emigration, the population appears to be steadily diminishing, and is now only about 6000, or less than half what it was in 1857. Unfortunately the island has hardly a regular harbour on any part of the coast; from its situation at the meeting, as it were, of seas, the currents in the neighbourhood are strong, and storms are very frequent. The best anchorage is at San Nicolo, at the middle of the eastern about 1500 inhabitants, at the southern extremity, with a bishop, side of the island. The principal village is Capsali, a place of and several convents and churches; the lesser hamlets are Modari, Potamo and San Nicolo.

There are comparatively few traces of antiquity, and the identification of the ancient cities has been disputed. The capital, which bore the same name as the island, was at PaleoKastro, about 3 m. from the present port of Avlemona. In the church of St Kosmas are preserved some of the archaic Doric columns of the famous temple of Aphrodite of Cythera, whose was here that worship had been introduced from Syria, and ultimately spread over Greece. According to the accepted story,

the goddess first landed when she emerged from the sea. At a
very early date Cythera was the seat of a Phoenician settlement,
established in connexion with the purple fishery of the neighbour-
ing coast; it is said that it was therefore called Porphyris
(cf. Pliny iv. 18, 19). For a time dependent on Argos, it became
afterwards an important possession of the Spartans, who annually
despatched a governor named the Cytherodices. In the Pelo-
ponnesian war, Nicias occupied the island, but in 421 it was
recovered by Sparta. Its modern history has been very much
the same as that of the other Ionian islands; but it was subject
See the works referred to under CEPHALONIA, and also Weil, in
to Venice for a much shorter period-from 1717 to 1797.
CYTISINE (Ulexin, Sophorin), CHNO, an alkaloid dis-
Mittheil. d. deutsch. Inst. zu Athen (1880), pp. 224-243.
covered in 1818 by J. B. Chevreul in the seeds of laburnum
(Cytisus Laburnum) and isolated by A. Husemann and W.
Marmé in 1865 (Zeit. f. Chemie, 1865, i.p. 161). It is also found
Euchresta horsfieldii. It is extracted from the seeds by an
in the seeds of furze (Ulex europaeus), Sophora tormentosa, and

alcoholic solution of acetic acid, and forms large crystals which melt at 153° C., and are easily soluble in water, alcohol and chloroform. It is a secondary and tertiary di-acid base, and is strongly alkaline in its reaction. Hydrogen peroxide oxidizes it to oxycytisine, C1HÂN,O2, chromic acid to an acid, CH,NO, and potassium permanganate to oxalic acid and ammonia. It acts as a violent poison.

|

See further, P. C. Plugge, Arch. der Pharm. (1891), 229, p. 48 et seq.; A. Partheil, Ber. (1890), 23, p. 3201, Arch. der Pharm. (1892), 230, p. 448; M. Freund and A. Friedmann, Ber. (1901), 34. p. 615; and J. Herzig and H. Meyer, Monats. f. Chem. (1897), 18, p. 379. CYTOLOGY (from AUTOS, a hollow vessel, and Xoyos, science), the scientific study of the "cells " or living units of protoplasm (q.v.), of which plants and animals are composed. All the higher, and the great majority of the lower, plants and animals are composed of a vast number of these vital units or cells." In the case of many microscopic forms, however, the entire organism, plant or animal, consists throughout life of a single cell. Familiar examples of these "unicellular "forms are Bacteria and Diatoms among the plants, and Foraminifera and Infusoria among the animals. In all cases, however, whether the cell-unit lives freely as a unicellular organism or forms an integral part of a multi- | cellular individual, it exhibits in itself all the phenomena char-prehensive cell-theory to include animal tissues was made by acteristic of living things. Each cell assimilates food material, whether this is obtained by its own activity, as in the majority of the protozoa, or is brought, as it were, to its own door by the blood stream, as in the higher Metazoa, and builds this food material into its own substance, a process accompanied by respiration and, excretion and resulting in growth. Each cell exhibits in greater or less degree "irritability," or the power of responding to stimuli; and finally each cell, at some time in its life, is capable of reproduction. It is evident therefore that in the multicellular forms all the complex manifestations of life are but the outcome of the co-ordinated activities of the constituent cells. The latter are indeed, as Virchow has termed them, "vital units." It is therefore in these vital units that the explanation of vital phenomena must be sought (see PHYSIOLOGY). As Verworn1 said, "It is to the cell that the study of every bodily function sooner or later drives us. In the muscle cell lies the problem of the heart beat and that of muscular contraction; in the gland cell reside the causes of secretion; in the epithelial cell, in the white blood corpuscle, lies the problem of the absorption of food, and the secrets of the mind are hidden in the ganglion cell." So also the problems of development and inheritance have shown themselves to be cell problems, while the study of disease has produced a I cellular pathology." The most important problems awaiting solution in biology are cell problems.

Historical. The cell-theory ranks with the evolution theory in the far-reaching influence it has exerted on the growth of modern biology; and although almost entirely a product of the 19th century, the history of its development gives place, in point of interest, to that of no other general conception. The cell-theory-in a form, however, very different from that in which we now know it was originally suggested by the study of plant structure; and the first steps to the formulation, many years later, of a definite cell-theory, were made as early as the later part of the 17th century by Robert Hooke, Marcello Malpighi and Nehemiah Grew. Hooke (1665) noted and described the vesicular nature of cork and similar vegetable substances, and designated the cavities by the term "cells." A few years later Malpighi (1674) and Grew (1682), still of course working with the low power lenses alone available at that time, gave a more detailed description of the finer structure of plant tissue. They showed that it consisted in part of little cell-like cavities, provided with firm cell-walls and filled with fluid, and in part of long tube-like vessels. A long time passed before the next important step forward was made by C. L. Treviranus, who, working on the growing parts of young plants, showed that the tubes and vessels of Malpighi and Grew arose from cells by the Allgemeine Physiologie, p. 53 (1895).

Vom inwendigen Bau der Gewächse (1806).

latter becoming elongated and attached end to end, the inter-
vening walls breaking down; a conclusion afterwards confirmed
by Hugo von Mohl (1830). It was not, however, until the
appearance of Matthias Jakob Schleiden's paper Beiträge zur
Phylogenesis (1838) that we have a really comprehensive treat-
ment of the cell, and the formulation of a definite cell-theory
for plants. It is to the wealth of correlated observations and
to the philosophic breadth of the conclusions in this paper that
the subsequent rapid progress in cytology is undoubtedly to be
attributed. Schleiden in this paper attempted to solve the
problem of the mode of origin of cells. The nucleus (vide infra)
of the cell had already been discovered by Robert Brown (1831),
who, however, failed to realize its importance. Schleidea
utilized Brown's discovery, and although his theory of phyto-
genesis is based on erroneous observations, yet the great import-
ance which he rightly attached to the nucleus as a cell-structure
made it possible to extend the cell-theory to animal tissues also.
We may indeed date the birth of animal cytology from Schleiden's
short but epoch-making paper. Comparisons between plant
and animal tissues had already been made by several workers,
among others by Johannes Müller (1835), and by F. G. J. Henle
and J. E. Purkinje (1837). But the first real step to a com-
Theodor Schwann. This author, stimulated by Schleiden's
work, published in 1839 a series of Mikroskopische Untersuchungen
über die Übereinstimmung in der Structur und dem Wachstum der
Tiere und Pflanzen. This epoch-making work ranks with
that of Schleiden in its stimulating influence on biological
research, and in spite of the greater technical difficulties in the
way, raised animal cytology at one blow to the position already,
and so laboriously, acquired by plant cytology. In the animal
cell it is the nucleus and not the cell-wall that is most con-
spicuous, and it is largely to the importance which Schwann,
following the example of Schleiden, attached to this structure
as a cell constituent, that the success and far-reaching influence of
his work is due. Another feature determining the success of
Schwann's work was his selection of embryonic tissue as material
for investigation. He showed that in the embryo the cells all
closely resemble one another, only becoming later converted
into the tissue elements-nerve cells, muscle cells and so forth-
as development proceeded; just as a similar mode of investiga-
tion had enabled Treviranus to trace the origin from typical cells
of the vascular tissue in plants more than 30 years previously.
And just as Treviranus showed that there was a union of cells
to form the vessels in plants, so Schwann now showed that a union
of cells frequently occurred in the formation of animal tissues.
So great was the stimulus given to cytological research by
the work of Schleiden and Schwann that these authors are often
referred to as the founders of the cell-theory. Their theory,
however, differed very greatly from that of the present time.
Not only did they suppose new cells to arise by a sort of " crystal-
lization "from a formative" mother liquor "or" cytoblastema"
(vide infra), but they both defined the cell as a " vesicle " provided
with a firm cell-wall and with fluid contents. The cell-wall was
regarded as the essential cell-structure, which by its own peculiar
properties controlled the cell-processes. The work of Schleiden
and Schwann marks the close of the first period in the history
of the cell-theory-the period dominated by the cell-wall. The
subsequent history is marked by the gradual recognition of the
importance of the cell-contents. Schleiden had noticed in the
plant cell a finely granular substance which he termed "plant
slime" (Pflanzenschleim). In 1846 Hugo von Mohl applied to
this substance the term "protoplasm "; a term already used
by Purkinje six years previously for the formative substance of
young animal embryos. Mohl showed that the young plant cell
was at first completely filled by the protoplasm, and that only
later, by the gradual accumulation of vacuoles in the interior,
did this substance come to form a thin layer on the inner surface
of the cell-wall. Mohl also described the spontaneous movement
of the protoplasm, a phenomenon already noted by Schleiden
for his plant slime, and originally discovered by Bonaventura
Corti in 1772 for the cells of Chara, and rediscovered in 1807

by Treviranus. Not only was attention thus gradually directed | plasmic continuity between the cells of the organism. This to the importance of the cell-contents, but observations were not continuity, which is effected by fine protoplasmic threads lacking, even in the plant kingdom, tending to weaken the ("cell-bridges") piercing the cell-wall and bridging the interimportance hitherto attached to the cell-wall. Among these may cellular spaces when these are present, is to be regarded as the be mentioned Cohn's observation that in the reproduction of morphological expression of the physiological interdependence Algal forms the protoplasm contracts away from the cell-wall of the various-often widely separated-tissues of the body." and escapes as a naked" swarm spore." Similarly in the animal It is probable that it is the specialization of this primitive kingdom instances began to be noted in which no membrane condition which has produced the cell-elements of the nervous appeared to be present (Kolliker, 1845; Bischoff, 1842), and for system. In many cases the cell-connexions are so extensive as some time it was hotly debated whether these structures could to obliterate cell-boundaries. A good example of such a "synbe regarded as true cells. As a result of the resemblance between cytial" tissue is provided by the heart muscle of Vertebrates the streaming movements in these apparently naked cells (e.g. and the intestinal musculature of Insects (Webber). lymphocytes) and those seen in plant cells, R. Remak was led In all multicellular, and in the great majority of unicellular, (1852-1853) to apply Mohl's term "protoplasm" to the sub- organisms the protoplasm of the cell-unit is differentiated into stance of these animal cells also. Similarly Max Schultze (1863) two very distinct regions,-a more or less central region, the and H. A. de Bary (1859), as a result of the study of unicellular nucleus, and a peripheral region (usually much more extenanimals, came to the conclusion that the substance of these sive), the cell-body or cytoplasm. This universal morphoorganisms, originally termed "Sarcode " by F. Dujardin, was logical differentiation of the cell-protoplasm is accompanied by identical with that of the plant and animal cell. Numerous corresponding chemical differences, and is the expression of a workers now began to realize the subordinate position of the physiological division of labour of fundamental importance. cell-wall (e.g. Nägeli, Alexander Braun, Leydig, Kolliker, Cohn, In some of the simpler unicellular organisms, e.g. Tetramitus, de Bary, &c.), but it is to Max Schultze above all that the credit the differentiated protoplasm is not segregated. Such forms is due for having laid the foundation of the modern conception are said to have a "distributed" nucleus, and among the of the cell-a conception often referred to as the proto-plasmic- Protozoa correspond to Haeckel's "Protista." It is probable theory in opposition to the cell-theory of Schleiden and that among plants the Bacteria and Cyanophyceae have a Schwann. Max Schultze showed that one and the same similar distributed nucleus. In all the higher forms, however, substance, protoplasm, occurred in unicellular forms and in the the segregation is well marked, and a "nuclear membrane higher plants and animals; that in plants this substance, separates the substance of the nucleus, or "karyoplasm 194 though usually enclosed within a cell membrane, was sometimes from the surrounding "cytoplasm." Within the nuclear naked (e.g. swarm spores), while in many animal tissues and membrane the karyoplasm is differentiated into two very in many of the unicellular forms the cell-membrane was always distinct portions, a clear fluid portion, the "karyolymph," and absent. He therefore concluded that in all cases the cell-mem- a firmer portion in the form of a coarser or finer "nuclear brane was unessential, and he redefined the "cell" of Schleiden reticulum." This latter is again composed of two parts, the and Schwann as "a small mass of protoplasm endowed with the "linin reticulum," and, embedded in the latter and often attributes of life" (1861). In the same year the physiologist | irregularly aggregated at its nodal points, a granular substance, Brücke maintained that the complexity of vital phenomena the "chromatin," the latter being the essential constituent necessitated the assumption for the cell-protoplasm itself of a of the nucleus. In addition to the chromatin there may be complex structure, only invisible because of the limitations of our present in the nucleus one or more, usually spherical, and as yet methods of observation. The cell in fact was to be regarded as somewhat enigmatical bodies, the "nucleoli." In addition to being itself an "elementary organism." By this time too it was the nucleus and cytoplasm, a third body, the "centrosome," realized that the formation of cells de novo, postulated by has often been considered as a constant cell-structure. It is Schleiden's theory of "phytogenesis," did not occur. Cells a minute granule, usually lying in the cytoplasm not far from only arose by the division of pre-existing cells,-as Virchow the nucleus, and plays an important part in cell-division and neatly expressed it in his since famous aphorism, omnis cellula fertilization (see below). e cellula. It was, however, many years before the details of this "cell-division " were laid bare (see Cell-Division below). General Morphology of the Cell.-In its simplest form the cell is a more or less spherical mass of viscid, translucent and granular protoplasm. In addition to the living protoplasm there is present in the cell food-material in various stages of assimilation, which usually presents the appearance of fine granules or spherules suspended in the more or less alveolar or reticular mesh-work of the living protoplasm. In addition there may be more or less obvious accumulations of waste material, pigment, oil drops, &c.-products of the cell's metabolic activity. All these relatively passive inclusions are distinguished from the living protoplasm by the term "metaplasm" (Hanstein), or "paraplasm" (Kupffer), although in practice no very sharp distinction can be drawn between them. The cell is frequently, but by no means always, bounded by a cell-wall of greater or less thickness. In plants this cell-wall consists of cellulose, a substance closely allied to starch; in animals only very rarely is this the case. Usually the cell-wall, when this is present, is a product of the cell's secretive activity; sometimes, however, it appears to be formed by an actual conversion of the surface layer of the protoplasm, and retains the power of growth by intussusception " like the rest of the protoplasm. Even when a limiting membrane is present, however, evidence is steadily accumulating to show that the cell is not an isolated physiological unit, but that, in the vast majority of cases, there is a protoThe Chromoplastids of the vegetable cell come under a different category of cell-inclusions; see PLANTS: Cytology.

66

Cell-differentiation.-Both among unicellular and multicellular individuals the cell assumes the most varied forms and performs the most diverse functions. In all cases, however, whether we examine the free-living shapeless and slowly creeping Amoeba, or the striped muscle cell or spermatozoon of the Metazoa (fig. 1, b and c), the constant recurrence of cytoplasm and nucleus show that we have to deal in each case with a cell. The variation in the form and structure of the cell is an expression of that universal economic law of nature, "division of labour," with its almost invariable accompanying "morphological differentiation "; the earliest and most fundamental example being in the differentiation of the cell-protoplasm into cytoplasm and nucleus. In multicellular individuals the division of labour to which the structural complexity of the organism is due is between the individual cell-units, some cells developing one

Cf. Pfeffer's classical experiments on the physiological significance of cell-continuity in plant tissues (Über den Einfluss des Zellkerns auf die Bildung der Zellhaut, 1896). The recent work in physiology on the influence substances secreted by certain tissues and circulating in the blood-stream exert upon other and widely different tissues, should not be lost sight of in this connexion.

The influence this protoplasmic continuity may have upon our conception of the cell as a unit of organization is referred to below (Present Position of the Cell-theory).

A term (from kapvov, kernel) suggested by Flemming to replace Strasburger's hybrid term nucleoplasm (1882). The earlier workers, e.g. Leydig, Schultze, Brücke, de Bary, &c., restricted the term protoplasm to the cell-body--the Cytoplasm" of Strasburger, an example still followed by O. Hertwig.

From linum, a thread, Schwarz, 1887.
From xpua, colour, Flemming, 1879.

aspect, some another, of their vital attributes. Thus one cell | uniform coating to the free surface of the cell, as in ciliated specializes in, say, secretion, another in contractility, another in receiving and carrying stimuli, and so forth, so that we have the gland cell, the muscle cell, and the nerve cell, each appropriately grouped with its fellows to constitute the particular tissue or organ-gland, muscle or brain-which has for its function that of its constituent cells. In unicellular animals we also find division of labour and its accompanying morphological differentiation, but here there is no subdivision of the protoplasm of the organism into the semi-autonomous units which so greatly facilitate division of labour in the Metazoa; instead, division of labour must be between different regions of protoplasm in the single cell. The sharply defined character of this regional differentiation in the Protozoa, and the surprising structural complexity it may produce, sufficiently clearly show that although multicellular structure has greatly facilitated regional differentiation in the Metazoa, it is by no means essential to this process (see below, Present Position of the Cell-theory).

It is not within the scope of this article to attempt a comprehensive review of the variety in structural complexity to which this division of labour among the cells of the Metazoan and the regional differentiation of the cell-bodies of the Protozoa has given rise. Some indication of the wealth of variety may be best given by taking a general survey of cell-modifications, grouped according to the cell-attributes the expression of which they facilitate.

(a) Structural Complexity facilitating Movement.-One of the most striking, and hence earliest described, of the fundamental attributes of protoplasm is its power of spontaneous movement. This is seen in the walled cell of plant tissue and in

From A. Gurwitsch, Morphologie und Biologie der Zelle, by permission of Gustay
Heidenhain.) b. Mucus-secreting "goblet "-cells. (After Gur-
FIG. 2.-Types of Cells. a, Ciliated epithelial cells. (After
witsch.)

and the flame cells of the Platyelmia (q.v.). In one group of
infusoria (Hypotricha), the cilia," cirri," have attained a high
degree of differentiation, and reach a considerable size. Both
cilia and flagella spring directly from the cell-protoplasm, piercing
the cell-membrane, when this is present. At the point where
they become continuous with the cell-body there is usually a
deeply staining "basal granule." In some cases the flagella
are in direct connexion with the centrosome (see below, Cell-
division), e.g. Trypanosoma and spermatozoa, in some cases even
while the centrosome is functioning in mitosis (e.g. insect
spermatogenesis, Henneguy2 and Meves (fig. 3).

In the ability of Amoeba to contract into a spherical mass, and in the presence in its protoplasm of the contractile vacuole, we see another type of spontaneous movement-contractilityof the protoplasm. In the "musculo-epithelial cells of Hydre,

From O. Hertwig, Allgemeine Biologie, by permission of Gustav Fischer.
FIG. 3.-Spermatocytes of Bombyx mori, showing the precocious
appearance of the spermatozoon flagellum and its relation to the
centrosome. (After Henneguy.)

the elongated basal portion of the cell alone possesses this
contractility. In the higher Metazoa the whole cell-muscle
cell-is specialized for contractility, and shows, as a result of
foreshadowed in the contractile regions of many Protozoa, eg,
its specialization, a distinct fibrillation. This fibrillation is

2" Sur les rapports des cils vibratiles avec les centrosomes," Archives d'anatomie microscopique (1898).

"Über Zentralkörper in männlichen Geschlechtszellen von Schmetterlingen" (Anat. Anz. Bd. xiv., 1897). Cf. also the papers of Lenhossek (Über Flimmerzellen, 1898), Karl Peter (Das Zentrum für die Flimm-und Giesselbewegung, 1899) and Verworn (Studies aut Physiologie der Flimmerbewegung, 1899).