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A membrane or layer of tissue that covers or envelops an organ or other anatomical structure.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(1) In animals, the peripheral layer of skin coverings of ascidians, salpids, and other animals of the subphylum Tunicata, phylum Chordata. The tunica is a thickened cuticle of cutaneous epithelium that is colonized by cells, a unique phenomenon in the animal kingdom. It serves to protect the internal organs.

The tunica is composed of tunicin, a carbohydrate closely related to cellulose. This substance has a gelatinous consistency, which makes possible the implantation in the tunica of cells that migrate from the cutaneous epithelium. In histological structure, the tunica resembles connective tissue with a gelatinous basal substance. Blood vessels may grow into the tunica. In appendicu-larians, the tunica separates from the body as the result of a process that resembles molting, forming a transparent gelatinous or chitinoid membrane, which serves as an outer covering of the animal or which is appended to the animal externally. This structure is adapted to filtering food particles out of seawater.

(2) In plants, one or more external layers of cells of formative tissue (meristem) covering the corpus of the growing point (apex) in the form of a vault. Dicotyledons have as many as five tunicae, while monocotyledons have as many as three.

Cell division in the tunica predominantly occurs anticlinally, or perpendicular to the surface of the organ; hence the surface of the tunica enlarges without change in the number of cell layers. The epidermis is usually formed from the outer layer of the tunica, which corresponds to the dermatogen according to the histogen theory of the German botanist J. von Hanstein; the primary cortex or part of it is formed from the inner layer of the tunica. The tunica-corpus theory was proposed by the German scientist A. Schmidt in 1924. Sometimes only the layers of cells located higher than the rudimentary leaves are called the tunica. The number of layers of the tunica sometimes increases gradually, but always remains a characteristic taxonomical feature of the plant.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Tunica vaginalis flap was raised off by incising tunica vaginalis near testicular lower pole and expanded upto the cord structures, taking care to avoid damage to the vas and vessels.
The tunica vaginalis testis consists of visceral, extending over the testis and epididymis, and the parietal layer (PL), lining the internal scrotal wall.
Yesil, "Fibrous pseudotumors of tunica albuginea, tunica vaginalis and epididymis: Report of two cases," Cancer Epidemiology, vol.
Morphological and microcirculatory evaluation of the rat testis after detorsion with or without a capsular release with a tunica vaginalis flap.
Izol, "Well-differentiated papillary mesothelioma of the tunica vaginalis: a case study and review of the literature," Korean Journal of Pathology, vol.
Malignant Mesothelioma of the Tunica Vaginalis: Presenting with Intermittent Scrotal Pain and Hydrocele.
Macroscopic changes in infected Actinobacillus Histophilus sheep (n = 10) seminis somni Abscess in the left epididymis tail 50% 50% Abscess in the left epididymis body 20% 40% Abscess in the right epididymis tail 10% 0% Scrotal swelling 10% 0% Fibrin in the pampiniform plexus 0% 30% Fibrinous periorchitis 20% 30% Hemorrhage adjacent left epididymis tail 20% 10% Tunica vaginalis thickening with fibrous 40% 60% adhesion Hypotrophy left testis 50% 10% Increase in volume of vesicular glands 30% 0% Increase in volume of the left urethral 10% 10% bulb Inguinal lymphadenomegaly 60% 20% Iliac lymphadenomegaly 50% 20% TABLE 3: Distribution, frequency, and intensity of inflammatory lesions in the genitourinary organs of rams experimentally infected with Actinobacillus seminis.
Following this, the patient underwent an excisional biopsy for what appeared to be a primary mesothelioma of the tunica vaginalis. At surgical exploration, there were two subcentimetre lesions on the surface of both testes.
The tunica vaginalis is usually thickened, with tumor coating it, or it is studded with nodules of varying size.
Two patients with simple repair and 2 nd layer with dartos had recurrence, two patients treated with OIU had recurrence and after that repair with tunica vaginalis cover was performed with no recurrence and none of the patients treated with OIU plus simple repair with dartos had recurrence.
According to the results of this study, relevant gubernaculums to scrotum starting to atrophy from days117.8 of age and in continuing of fetal growth is atrophied completely and at birth time, which is converted to the ligament that adhered tail of epididymis and tunica vaginalis to the scrotum wall.
You will also learn that the bluish discoloration of the parietal layer of the tunica vaginalis is due to the Raman effect, another patriotic chestnut.