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organs; with a stomodaeum; with a mesenchyma which is partly gelatinous but partly cellular; with eight meridianal rows of vibratile paddles formed of See also:

long fused or matted See also:

CILIA (plural of Lat. cilium, eyelash)

cilia; lacking nematocysts (except in one genus). An example See also:

COMMON

common on the See also:

BRITISH

British coasts is furnished by Hormiphora (Cydippe). In outward form this is an See also:

egg-shaped See also:

ball of clear jelly, having a mouth at the pointed (oral) See also:

pole, and a sense-See also:

ORGAN

organ at the broader (ab- oral) pole. It possesses eight meridians (costae) of iridescent paddles in See also:

CONSTANT, BENJAMIN (1845-1902)

constant vibration, which run from near one pole towards the other; it has also two pendent feathery tentacles of considerable length, which can be retracted into pouches. The mouth leads into an ectodermal stomodaeum (" See also:

STOMACH (Gr. vrbsaxos from arbga, a mouth)

stomach "), and the latter into an endodermal See also:

FUNNEL (through an O. Fr. founil, found in Breton, from Lat. infundibulum, that through which anything is poured, from fundere, to pour)

funnel (infundibulum); these two are compressed in planes at right angles to one another, the sectional long See also:

AXIS (Lat. for " axle ")

axis of the stomodaeum lying in the so-called sagittal (stomodaeal or gastric) See also:

PLANE

plane, that of the funnel in the trans-See also:

VERSE (from Lat. versus, literally a line or furrow drawn by turning the plough, from vertere, and afterwards signifying an arrangement of syllables into feet)

verse (tentacular or funnel) plane. From the funnel, canals are given off in three directions; (a) a pair of paragastric (stomachal, or stomodaeal) canals run orally, parallel to the stomodaeum, and end blindly near the mouth; (b) a pair of perradial canals run in the transverse plane towards the See also:

EQUATOR (Late Lat. aequator, from aequare, to make equal)

equator of the See also:

animal; each of these becomes divided into two See also:

SHORT, FRANCIS JOB (1857– )

short canals at the See also:

BASE

base of the tentacle sheath which they See also:

SUPPLY (through Fr. from Lat. supplere, to fill up)

supply, but has previously given off a pair of short interradial canals, which again bifurcate into two adradial canals; all these branches See also:

lie in the See also:

EQUATORIAL

equatorial plane of the animal, but the eight adradial canals then open into eight meridianal canals which run orally and aborally under the costae; (c) a pair of aboral vessels which run towards the sense-organ, each of which bifurcates; of the four vessels thus formed, two only open at the sides of the sense-organ, forming the so-called excretory apertures.

These three sets of structures, with the funnel from which they rise, make up the endodermal coelenteron, or gastro-vascular See also:

SYSTEM

system. The generative organs are endodermal by origin, See also:

BORNE, KARL LUDWIG (1786–1837)

borne at the sides of the meridianal canals as indicated by the signs c? ?. There exists a subepithelial plexus with See also:

NERVE (Lat. nervus, Gr. vevpov, a bowstring)

nerve cells A, Ad radial canals. F, Infundibulum. I, Interradial See also:

canal. M, Meridianal canal lying under a See also:

costa. N, Ciliated furrow from sense pole to costa. Pg, Paragastric canal. SO, Sense-organ. St, Stomodaeum. Subs, Subsagittal costa.

Subt, Subtentacular costa. T, Tentacle. Ts, Boundaries of tentacle-sheath. and See also:

fibres, similar to that of jelly-fishes. The sense-organ of the aboral pole is complex, and lies under a See also:

DOME (Lat domus, house; Ital. duomo, cathedral)

dome of fused cilia shaped like an inverted See also:

bell-See also:

jar; it consists of an otolith, formed of numerous calcareous spheroids, which is supported on four plates of fused cilia termed balancers, but is otherwise See also:

FREE

free. The ciliated ectoderm below the organ is markedly thickened, and perhaps functionally represents a nerve-ganglion: from it eight ciliated furrows radiate outwards, two passing under each balancer as through an archway, and diverge each to the See also:

head of a meridianal costa. These ciliated furrows stain deeply with osmic See also:

ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid, and See also:

NERVOUS

nervous impulses are certainly transmitted along them. Locomotion is effected by strokes of the paddles in an aboral direction, See also:

DRIVING (from " to drive," i.e. generally to propel, force along or in, a word common in various forms to the Teutonic languages)

driving the animal mouth forwards through the See also:

WATER

water: each See also:

PADDLE

paddle or See also:

COMB (a word common in various forms to Teut. languages, cf. Ger. Kamm, the Indo-Europ. origin of which is seen in yoµros, a peg or pin, and Sanskrit, gambhas, a tooth)

comb (Gr. «-refs; hence Ctenophora) consists of a See also:

PLATE

plate of fused or matted cilia set transversely to the costa. The myoepithelial cells (formerly termed neuro-See also:

MUSCULAR

muscular cells), characteristic of other Coelentera, are not to be found in this group. On the other See also:

hand there are well-marked muscle fibres in definite layers, derived from See also:

SPECIAL

special niesoblastic cells in the embryo, which are embedded in a jelly; these in their origin and arrangement are quite comparable to the mesoderm of Triploblastica, and, although the muscle-cells of some jelly-fish exhibit a somewhat similar See also:

CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition, nothing so highly specialized as the mesenchyme of Ctenophora occurs in any other Coelenterate. The nematocysts being nearly absent from their group, their See also:

CHIEF (from Fr. chef, head, Lat. caput)

chief See also:

FUNCTION

function is carried out by adhesive See also:

lasso-cells.

The Ctenophora are classified as follows: Subclass i. Tentactlata, See also:

Order I. CYDIPPIDEA, Hormiphora. „ 2. LOBATA, Deiopea. 3. CESTOIDEA, Cestus. ii. Nuda, „ Beroe. The Tentaculata, as the name implies, may be recognized by the presence of tentacles of some sort. The CYDIPPIDEA are generally spherical or ovoid, with two long retrusible pinnate tentacles: the meridianal and paragastric canals end blindly. An example of these has already been briefly described.

The LOBATA are of the same See also:

general type as the first Order, except for the presence of four circumoral auricles (processes of the subtransverse costae) and of a pair of sagittal outgrowths or lobes, on to which the subsagittal costae are continued. Small See also:

ACCESSORY

accessory tentacles lie in grooves, but there is no tentacular pouch; the meridianal vessels anastomose in the lobes. In the CESTOIDEA the See also:

BODY

body is compressed in the trans-verse plane, elongated in the sagittal plane, so as to become ribandlike: the subtransverse costae are greatly reduced, the subsagittal costae extend along the aboral edge of the riband. The subsagittal canals lie immediately below their costae aborally, but continuations of the subtransverse canals See also:

ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round down the See also:

MIDDLE

middle of the riband, and at its end unite, not only with the subsagittal but also with the paragastric canals which run along the oral edge of the riband. The tentacular bases and pouches are See also:

PRESENT

present, but there is no See also:

main tentacle as in Cydippidea; See also:

FINE

fine accessory tentacles lie in four grooves along the oral edge. The subclass Nuda have no tentacles of any See also:

KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind; they are conical or ovoid, with a capacious stomodaeum like the cavity of a See also:

THIMBLE

thimble. There is a coelenteric network formed by anastomoses of the meridianal and paragastric canals all over the body. The See also:

EMBRYOLOGY

embryology of Callianira has been.worked out by E. Mechnikov. Segmentation is See also:

COMPLETE

complete and unequal, producing macromeres and micromeres marked by See also:

DIFFERENCES, CALCULUS OF (Theory of Finite Differences)

differences in the See also:

SIZE

size and in yolk-contents. The micromeres give rise to the ectoderm; each of the sixteen macromeres, after budding off a small mesoblast See also:

CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell, passes on as endoderm. A gastrula is established by a mixed See also:

PROCESS

process of embole and epibole.

The mesoblast cells travel to the aboral pole of the embryo, and there form a See also:

CROSS

cross-shaped See also:

mass, the arms of which lie in the sagittal and transverse planes (perradii). There can be but little question of the propriety of including Ctenophora among the Coelentera. The undivided coelenteron (gastro-vascular system) which constitutes the See also:

SOLE (Solea)

sole cavity of the body, the largely radial symmetry, the presence of endo- Subs, Subsagittal costae. Pg, Continuation of the See also:

para- Subt, Much reduced subtenta- gastric canal at right cular costae. angles to its See also:

ORIGINAL

original direc- Subt, See also:

BRANCH (from the Fr. branche, late Lat. branca, an animal's paw)

Branch of the subten- tion along the See also:

LOWER

lower edge tacular canal which runs of the riband. At the along the centre of the right-hand end the last riband. two are seen to unite with the subsagittal canal. dermal generative organs on the coelenteric canals, the sub-See also:

EPITHELIAL, ENDOTHELIAL

epithelial nerve-plexus, the mesogloea-like See also:

MATRIX

matrix of the body—all these features indicate See also:

affinity to other Coelentera, but, as has been stated in the See also:

ARTICLE (from Lat. articulus, a joint)

article under that See also:

TITLE (0. Fr. title, mod. titre, from Lat. titulus)

title, the relation is by no means See also:

close. At what See also:

period the Ctenophora branched off from the See also:

LINE

line of descent, which culminated in the See also:

HYDROMEDUSAE

Hydromedusae and Scyphozoa of to-See also:

day, is not clear, but it is practically certain that they did so before the point of divergence of these two See also:

groups from one another. The See also:

PECULIAR

peculiar sense-organ, the specialization of the cilia into paddles with the corresponding modifications of the coelenteron, the See also:

anatomy and position of the tentacles, and, above all, the See also:

CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character and mode of formation of the mesenchyme, See also:

SEPARATE

separate them widely from other Coelentera. The last-named character, however, combined with the See also:

DISCOVERY

discovery of two remarkable organisms, Coeloplana and Ctenoplana, has suggested affinity to the See also:

FLAT (a modification of O. Eng. flet, an obsolete word of Teutonic origin, meaning the ground beneath the feet)

flat-See also:

WORMS

worms termed Turbellaria. Ctenoplana, the best known of these, has recently been redescribed by A. Willey (Quart. Journ.

Micr. Sci. xxxix., 1896). It is flattened along the axis which unites sense-organ and mouth, so . as to give it a dorsal (aboral) See also:

SURFACE

surface, and a ventral (oral) surface on which it frequently creeps. Its costae are very short, and retrusible; its two tentacles are pinnate and are also retrusible. Two crescentic rows of ciliated papillae lie in the transverse plane on each exhibits six lobes, two of which Willey (After Chun.) identifies with the stomodaeum of other Ctenophora; the other four give rise to a system of anastomosing canals such as are found in Beroe and Polyclad Turbellaria. An aboral See also:

VESSEL (O. Fr. vaissel, from a rare Lat. vascellum, dim. of vas, vase, urn)

vessel embraces the sense-organ, but has no See also:

EXTERNAL

external opening. Ctenoplana is obviously a Ctenophoran flattened and of a creeping See also:

HABIT (through the French from Lat. habitus, from habere, to have, hold, or, in a reflective sense, to be in a certain condition; in many of the English senses the French use habitude, not habit)

habit. Coeloplana is of similar form and habit, with two Ctenophoran tentacles: it has no costae, but is uniformly ciliated. These two forms at least indicate a possible stepping-See also:

stone from Ctenophora to T (centrally), Tentacular canal, and (distally) tentacle. Position of testes. Position of ovaries; other letters as in fig. 1.

The stomodaeum lies in the sagittal plane, the funnel and tentacles in the transverse or tentacular plane. d 594 Turbellaria, that is to say, from diploblastic to triploblastic Metazoa. By themselves they would present no very weighty See also:

ARGUMENT

argument for this line of descent from two-layered to three-layered forms, but the coincidences which occur in the development of Ctenophora and Turbellaria,—the methods of segmentation and gastrulation, of the separation of the mesoblast cells, and of mesenchyme formation,—together with the marked similarity of the adult mesenchyme in the two groups, have led many to accept this See also:

PEDIGREE

pedigree. In his Monograph on the Polyclad Turbellaria of the Bay of Naples, A. See also:

Lang regards a Turbellarian, so to say, as a Ctenophora, in which the sensory pole has rotated forwards in the sagittal plane through 9o° as regards the original oral-aboral axis, a rotation which actually occurs in the development of Thysanozoon (See also:

Muller's larva); and he See also:

SEES

sees, in the eight lappets of the preoral ciliated See also:

RING (O.E. hring; a word common to Teutonic languages; and probably cognate with the Lat. circus, Gr. KtpKOS or KpLKOS, Skt'. chakra, wheel, circle, cf. also " harangue "); in art, a band of circular shape of varying sizes, made of any material and used f

ring of such a larva, the rudiments of the costal plates. According to his view, a See also:

SIMPLE

simple See also:

early Turbellarian larva, such as that of Stylochus, most nearly represents for us to-day that ancestor from which Ctenophora and Turbellaria are alike derived. For details of this brilliant theory, the reader is referred to the original monograph. ntstehung der Geschlechtsorgane bei den Ctenophoren.," Zeitschr. Wiss. Zool. Ixix. pp. 472-491; K.

C. See also:

Schneider, Lehrbuch der vergleich. Histologie (1902). (G. H.

End of Article: CTENOPHORA

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