noun
definition
A bag or pouch inside a plant or animal that typically contains a fluid.
Examples of sac in a Sentence
This sac has been already referred to as a coelomoduct.
Thus, in Philaemon pungens (Lambert) it has the form of a large sac, into which open by a single orifice the conjoined oviducts.
The Gastropoda are mainly characterized by a loss of symmetry, produced by torsion of the visceral sac. This torsion may be resolved into two successive movements.
Each renal organ is a sac lined with glandular epithelium (ciliated cell, with concretions) communicating with the exterior by its papilla, and by ce, Cerebral ganglia.
In the majority of the Megascolicidae each sac is provided with one or more diverticula, tubular or oval in form, of a slightly different histological character in the lining epithelium, and in them is invariably lodged the sperm.
In Clausilia, according to the observations of C. Gegenbaur, the primitive shell-sac does not flatten out and disappear, but takes the form of a flattened closed sac. Within this closed sac a plate of calcareous matter is developed, and after a time the upper wall of the sac disappears, and the calcareous plate continues to grow as the nucleus of the permanent shell.
But whilst in Trematoda a digestive sac is invariably present except in the sporocyst larval stage, the Cestodes possess no trace of this organ at any stage of their development.
A, Fasciola hepatica, from the ventral surface (X 2); the alimentary and nervous systems only shown on the left side of the figure, the excretory only on the right; a, right main branch of the intestine; c, a diverticulum; g, lateral ganglion; n, lateral nerve; o, mouth; p, pharynx; s, ventral sucker; cs, cirrus sac; d, left anterior dorsal excretory vessel; m, main vessel; v, left anterior ventral trunk; x, excretory pore.
The sole difference is therefore that in Eudrilus the ovarian sac gives rise to a tube which bifurcates, one branch meeting a corresponding branch of the other ovary of the pair, while the second branch reaches the exterior.
Below the surface these walls are excavated with blood-vessels, so that the sac is practically a series of blood-vessels covered with renal epithelium, and forming 6 Cephalic tentacle.
The odontophore is powerfully developed; the radular sac is extraordinarily long, lying coiled in a space between the mass of the liver and the muscular foot.
To the left of the ctenidium a pulmonary sac, separated from it by an incomplete septum, am phibious.
Visceral sac and shell coiled in one plane; foot divided transversely into two parts, posterior part bearing an operculum, anterior part forming a fin provided with a sucker.
Visceral sac and shell small in proportion to the rest of the body, which cannot be withdrawn into the shell; foot elongated, fin-shaped, with sucker, but without operculum.
Q, Sac containing nutritive mb, Mantle-skirt.
Close to them is the remarkable dart-sac ps, a thick-walled sac, in the lumen of which a crystalline four-fluted rod or dart consisting of carbonate of lime is found.
It is clear enough that the sac is of a different origin from that of Aplysia (described in the section treating of Opisthobranchia), being primitive instead of secondary.
Whether the closed primitive shell-sac of the slugs (and with it the transient embryonic shell-gland of all other Mollusca) is precisely the same thing as the closed sac in which the calcareous pen or shell of the Cephalopod Sepia and its allies is formed, is a further question which we shall consider when dealing with the Cephalopoda.
It is important here to note that Clausilia furnishes us with an exceptional instance of the continuity of the shell or secreted product of the primitive shell - sac with the adult shell.
The mass of the arch-enteron or invaginated endodermal sac has taken on a bilobed form, and its cells are swollen (gs and tge).
This bilobed sac becomes entirely the liver in the adult; the intestine and stomach are formed from the pedicle of invagination, whilst the pharynx, oesophagus and crop form from the stomodaeal invagination ph.
Here the pits split into two, one part ending in a sac lined with sensory epithelium, and embedded in nervous tissue, the other projecting backwards as a long, glandular, blind canal.
When mature, each sac pushes out a process to the exterior, and this forms the genital duct.
It consists of a definite contractile sac or sacs lying on the dorsal side of the alimentary canal near the oesophagus, and in preparations of Terebratulina made by quickly removing the viscera and examining them in sea-water under a microscope, he was able to count the pulsations, which followed one another at intervals of 30-40 seconds.
Besides the four chief orders of friars there were the Crutched Friars in the parish of St Olave, Hart Street (about 1298), and the Friars of the Sac first outside Aldersgate (about 1257) and afterwards in the Old Jewry.
The digestive system consists of a simple or bifurcated sac, opening through the mouth by means of a "pharynx bulbosus," adapted to act primarily as a sucker, and secondarily, when drawing blood, as an aspirator.
They ingest the mucus and, to some extent, the blood of their host by the aid of a sucking pharynx through which the food passes into the bifurcated alimentary sac and its branched caeca.
The alimentary sac is simple elegans from the fins of and devoid of caeca.
The intestinal sac has become bifid and is usually devoid of branches.
The cilia are lost, the eye-spots disappear, the digestive sac vanishes and the larva becomes a sac or "sporocyst" full of germ-cells.
The exchange of fluid in the sac may well have a respiratory significance, in addition to its object of facilitating the movements of the tentacles.
By Isolda, granddaughter of Robert de Cardinan, the town was given to Richard, king of the Romans, who in the third year of his reign granted to the burgesses a gild merchant sac and soc, toll, team and infangenethef, freedom from pontage, lastage, &c., throughout Cornwall, and exemption from the jurisdiction of the hundred and county courts, also a yearly fair and a weekly market.
Their descendants styled themselves of Berkeley, and in 1200 the town was confirmed to Robert of Berkeley with toll, soc, sac, &c., and a market on whatever day of the week he chose to hold it.
But in Tobit we find Asmodaeus the evil demon, TO 7rovrlpov Sac,uoviov, who strangles Sarah's husbands, and also a general reference to " a devil or evil spirit," 77/€144,a.
On the other hand, the ejaculatory duct with its verticillate sac in the male of Cypris and other genera is a feature scarcely less remarkable.
At its posterior margin the peritoneum of the great sac is reflected on to the diaphragm to form the anterior layer of the coronary ligament.
To the left of the vena cava is the Spigelian lobe, which lies in front of the bodies of the tenth and eleventh thoracic vertebrae, the lesser sac of peritoneum, diaphragm and thoracic aorta intervening.
Pore leading from the pericardium into the glandular sac of the left nephridium.
Each nephridium in the oyster is a pyriform sac, which communicates by a narrow canal with the urino-genital groove placed to the front of the great adductor muscle; by a second narrow canal it communicates with the pericardium.
From all parts of the pyriform sac narrow stalk-like tubes are given off, ending in abundant widely-spread branching glandular caeca, which form the essential renal secreting apparatus.
The special gland of the musk-deer, which has made the animal so well known, and has proved the cause of unremitting persecution to its possessor, is found in the male only, and is a sac about the size of a small orange, situated beneath the skin of the abdomen, the orifice being immediately in front of the preputial aperture.
Unlike the cells of Protozoa, these embryonic cells of the Metazoa do not remain each like its neighbour and capable of independent life, but proceed to arrange themselves into two layers, taking the form of a sac. The cavity of the two-cell-layered sac or diblastula thus formed is the primitive gut or arch-enteron.
In the Coelentera, whatever subsequent changes of shape the little sac may undergo as it grows up to be polyp or jelly-fish, the original arch-enteron remains as the one cavity pervading all regions of the body.
When this covering is complete the shell is contained in a closed sac and is said to be " internal," but the sac is lined by ectoderm and the shell is always morphologically external.
The orifice of invagination (blastopore) narrows, and we now have a two-cell-layered sac - the gastrula.
Within this muscular tube lies a parenchymatous tissue which may be uniform (Cestodes) or differentiated into a central or digestive, and a peripheral portion (some Turbellaria), or finally the central portion becomes tubular and forms the digestive sac (Trematodes), while the peripheral portion is separated from it by a space lined in some forms by a flattened epithelium (most Planarians).
It is characteristic of the group that the mouth should be the only means of ingress to and egress from the digestive sac and that no true perivisceral space or coelom exists in the sense in which these terms are used in higher Invertebrates.
The study of Rhabdocoels (7) has led to the important discovery that the rudiment of the gonads and that of the pharynx are the first organs to appear, and that the alimentary sac arises independently of them.
For the use of the oculist, who constantly employs this drug, it is also prepared in lamellae for insertion within the conjunctival sac. Each of these contains one-thousandth part of a grain of physostigmine sulphate, a quantity which is perfectly efficient.
The stomach is formed upon much the same principle as that of the horse or rhinoceros, but is more elongated transversely and divided by a constriction into two cavities - a large left cul de sac, lined by a very dense white epithelium, and a right pyloric cavity, with a thick, soft, vascular lining.