The epithelial layer consists of (1) so-called " indifferent " cells secreting the perisarc or cuticle and modified to form glandular cells in places; for example, the adhesive cells in the foot.
Belonging primarily to the epithelial layer, the muscular cells may become secondarily sub-epithelial.
The sub-epithelial layer consists primarily of the so-called inter stitial cells, lodged between the narrowed basal portions of the epithelial cells.
The sub-epithelial layer thus primarily constituted may be recruited by immigration from without of other FIG.
Schulze.) elements, more especially by nervous (ganglion) cells and musclecells derived from the epithelial layer.
In its fullest development, therefore, the sub-epithelial layer consists of four classes of cellelements.
The muscular tissue consists primarily of processes from the bases of the epithelial cells, processes which are contractile in nature and may be distinctly striated.
A further stage in evolution is that the muscle-cells lose their connexion with the epithelium and come to lie entirely beneath it, forming a sub-epithelial contractile layer, developed chiefly in the tentacles of the polyp. The of the evolution of the ganglioncells is probably similar; an epithelial cell develops processes of nervous nature from the base, which come into connexion with the bases of the sensory cells, with the muscular cells, and with the similar processes of other nerve-cells; next the nerve-cell loses its connexion with the outer epithelium and becomes a sub-epithelial ganglion-cell which is closely connected with the muscular layer, conveying stimuli from the sensory cells to the contractile elements.
The ectoderm furnishes the general epithelial covering of the body, and the muscular tissue, nervous system and sense-organs.
The muscle-fibres arise as processes from the bases of the epithelial cells; such cells may individually become sub-epithelial in position, as in the polyp; or, in places where muscular tissue is greatly developed, as in the velum or sub-umbrella, the entire muscular epithelium may be thrown into folds in order to increase its surface, so that a deeper sub-epithelial muscular layer becomes separated completely from a more superficial bodyepithelium.
The nervous system of the medusa consists of sub-epithelial ganglion-cells, which form, in the first place, a diffuse plexus of nervous tissue, as in the polyp, but developed chiefly on the subumbral surface; and which are concentrated, in the second place, to form a definite central nervous system, never found in the polyp. In Hydromedusae the central nervous system forms two concentric nerverings at the margin of the umbrella, near the base of the velum.
The sensory cells are slender epithelial cells, often with a cilium or stiff protoplasmic process, and should perhaps be regarded as the only ectoderm-cells which retain the primitive ciliation of the larval ectoderm, otherwise lost in all Hydrozoa.
Ordinary indifferent cells of the epithelium containing pigment-granules, and (2) visual cells, slender sensory epithelial cells of the usual type, which may develop visual cones or rods at their free extremity.
The sub-epithelial tissues, i.e.
Adult without shell; a sub-epithelial pseudoconch formed by connective tissue; pallial cavity ventral.
The whole sac, with its epithelial wall and its contained genital cells, arises ultimately from some of the parenchymatous cells of the body.
A characteristic feature of cancer is the carrying of the epithelial cells (which are the essential element of the growth) to the nearest lymphatic glands, and in cancer of the stomach the secondary implication of the glands may cause the formation of large masses between the stomach and the liver, which may press upon the large veins and give rise to dropsy.
The same inter-communication prevails between adjacent cells in some animal tissues, and more particularly in those which are pathological, as in the case of the epithelial cells of cancer.
1 to 6 are from the epithelial cells of a cancer of the mamma, (After Galeotti.) „ 7 to 21 are from a sarcoma.
- Resting epithelial cell.
The epithelial cells are then able to pass from their normal position, in consequence of which they proliferate and at the same time revert to a more primitive type of cell.
Not only is this true of epithelial cells, but - the connective tissuecells of the supporting structure of cancerous growth, after repeated transplantation, may become so altered that a gradual evolution of apparently normal connective tissue into sarcomatous elements takes place, these giving rise to " mixed tumours."
The sarcomatous development may even completely outgrow the epithelial elements and so form and continue to grow as a pure sarcoma.
Black droplets of oil are seen in the epithelial cells lining the secreting tubules.
In the case of the squamous epithelial cancer of the anterior abdominal wall found so frequently in the natives of Kashmir, the position of the cancer is peculiar to this people, and is due to the chronic irritation following on repeated burns from using the " kangri " - a small earthenware vessel containing a charcoal fire enclosed in basket-work, and suspended round the waist, to assist in maintaining warmth in the extreme cold of the hills of Kashmir.
By mucoid is understood a soft gelatinous substance containing mucin, or pseudomucin, which is normally secreted by the epithelial cells of both the mucous membranes and glands.
This term is usually applied to a semi-solid substance of homogeneous and gelatinous consistence, which results partly from excretion and partly from degeneration of cellular structures, more particularly of the epithelial type.
Serous degeneration is met with in epithelial cells in inflammatory conditions and following on burns.
The free fatty acid radicle then unites with an alkali, and becomes transformed into a soluble soap which is then readily absorbed in this fluid condition by the epithelial cells of the mucous membrane.
418, also, Manual of General Pathology (London, 1898); Loeb, " Certain Activities of the Epithelial Tissue of Skin of Guinea-pig, &c.," Johns Hopkins Hosp. Bull., Balt.
Thrombosis is an accident of not dissimilar character, whereby a vessel is blocked not by a travelling particle, but by a clotting of the blood in situ, probably on the occasion of some harm to the epithelial lining of the vessel.
The epidermis has lost its connected epithelial character and its cilia, and the isolated cells have become sunk inwards retaining their S t- FIG.
The life of the parasites while in the insect is characterized by an alternation of active periods, during which multiplication goes on, with resting-periods, when the Trypanosomes become attached to the epithelial cells of the host.
F.e., Frontal epithelium; l.f.e'., l.f.e"., the two rows of latero-frontal epithelial cells with long cilia; ch, chitinous tubular lining of the filament; lac., blood lacuna traversed by a few processes of connective tissue cells; b.c., blood-corpuscle.
Epithelial cells with long cilia.
H, Epithelial cells filled with pigment.
Rudimentary cephalic eyes occur in the Mytilidae and in Avicula at the base of the first filament of the inner gill, each consisting of a I pigmented epithelial fossa containing a cuticular lens.
This byssus is not homologous with that of other Lamellibranchs, but originates from a single glandular epithelial cell embedded in the tissues on the dorsal anterior side of the adductor muscle.
Deep to these is the ovarian stroma, composed of fibrous tissue, and embedded in it are numerous nests of epithelial cells, the Graafian follicles, in various stages of development.
The Fallopian tubes, like many other tubes in the body, are made chiefly of unstriped muscle, the outer layer of which is longitudinal and the inner circular; deep to this are the submucous and mucous coats, the latter being lined with ciliated epithelium '(see' Epithelial Tissues), and thrown into longitudinal pleats.
About the fifth week of human embryonic life the tunica albuginea appears in the male, from which septa grow to divide the testis into lobules, while the epithelial cords form the seminiferous tubes, though these do not gain a lumen until just before puberty.
In the female the same growth of epithelial cords into the mesenchyme of the genital ridge takes place, but each one is Neural tube.
The tegmentum is pierced by numerous vertical ramified canals which contain epithelial papillae of the epidermis.
The labial commissure gives off a subradular commissure which also bears two ganglia, these being in close relation to a special sense-organ called the subradular organ, an epithelial projection with nerve-endings, lying in front of the radula and probably gustatory in function.
The cuticle, in some species very thick, contains numerous spicules which are long, hollow and calcified; they are secreted by epithelial papillae.
With regard to sense organs the epithelial papillae of the mantle have been mentioned.
The diseases to which the application has been hitherto confined are papillomata, lupus vulgaris, epithelial tumours, syphilitic ulcers, pigmentary naevi, angiomata, and pruritus and chronic itching of the skin; but the use of radium in therapeutics is still experimental.
The ovaries are epithelial sacs which open into the uteri.
We may regard it as a form of unipolar immigration in which the immigrating cells pass into the interior in a connected epithelial layer, instead of going in singly and independently.
Such cells, made up of epithelial and muscular components, are known as epithelio-muscular or myo-epithelial cells.