The hamsters all possess cheek-pouches, which are, however, absent in many of the following genera.
The cheeks are provided with large pouches opening externally.
Hence the gonads are found on the manubrium in Anthomedusae generally; on the base of the manubrium, or under the gastral pouches, or in both these situations (Octorchidae), or under the radial canals, in Trachomedusae; under the gastral pouches or radial canals, in Narcomedusae.
Among other important genera Cricetomys and Eosaccomys (both African) stand apart by the possession of cheek-pouches: C. gambianus being a very large species.
In the female the ovary is a large unpaired organ from the anterior end of which arise two oviducts, and connected with the latter are a pair of large so-called copulatory pouches, which perhaps act as receptacula seminis.
In addition to their stout build and long thickly haired tails, marmots are characterized by the absence of cheek-pouches, and the rudimentary first front-toe, which is furnished with a flat nail, as well as by certain features of the skull and cheek-teeth.
Paired archenteric pouches FIG.
In this order the radial canals are represented only by wide gastric pouches, and in the family Solmaridae are suppressed altogether, so that the tentacles and the festoons of the ring-canal arise directly from the stomach.
Cunoctantha fowleri Browne, buds are formed from the sub-umbrella on the under side of the stomach pouches, where later the gonads are developed.
No gastric pouches; the numerous tentacles arise direct from the stomach, into which also the peronial canals open, so that the ring-canal is cut up into separate festoons.
The sexes are distinct, as in all Streptoneura; and genital ducts and accessory glands and pouches are present, as in all Pectinibranchia.
In the marine Streptoneura they are ectodermic projections which ultimately fall off; in the Opisthobranchs they are closed pouches; in Paludina and Bithynia they are canals as in Pulmonata.
No doubt can be entertained that the greater part of the inner layer corresponds to the mesoderm of more ordinary embryos, for the coelomic pouches, the germ-cells, the musculature and the vascular system all arise from it.
The nuchal skeleton is a non-cellular laminated thickening of basement-membrane underlying that portion of the stomochord which lies between the above-mentioned pouches and the orifice into the throat.
There are, therefore, as many gill-pouches as there are gill-slits and as many gill-pores as pouches.
In the direct development Bateson showed that the three divisions of the coelom arise as pouches constricted off from the archenteron or primitive gut, thus resembling the development of the mesoblastic somites of Amphioxus.
In the cheeks are tolerably capacious pouches, which appear to be used as receptacles for food.
They appear at first to deposit what they have thus collected in their cheek pouches, and when these are filled they rise to the surface and quietly triturate their meal with the horny teeth before swallowing it.
Castoreum is a substance contained in two pear-shaped pouches situated near the organs of reproduction, of a bitter taste and slightly foetid odour, at one time largely employed as a medicine, but now used only in perfumery.
Flowers with nectar concealed by pouches, hairs, &c. Regular flowers predominate, e.g.
The hamsters, of which there are several kinds, are short-tailed rodents, with large cheek-pouches, of which the largest is the common C. frumentarius.
7) possess a pair of aurioles, great eversible ciliated pouches a little above the disk, utilized in swimming.
Fissure between the free edge water forms which carry the young in brood-pouches formed by the ctenidia have suppressed this larval phase.
Long, which is sharply bent upon itself two or three times, and also has several short, sac-like pouches or diverticula.
In hares and pacas the inside of the cheeks is hairy; and in some species, pouched rats and hamsters, there are large internal cheek-pouches lined with hair, which open near the angles of the mouth and extend backwards behind the ears.
In the New World pouched rats (Geomyidae) the pouches open externally on the cheeks.
The peculiar odour evolved by many rodents is due to the secretions of special glands, which may open into the prepuce, as in Mus, Microtus and Cricetus, or into the rectum, as in Arctomys and Thryonomys, or into the passage common to both, as in the beaver, or into pouches opening near the vent, as in hares, agoutis and jerboas.
The genus which is common to the northern parts of both hemispheres is distinguished by the large cheek-pouches and by the absence or rudimentary condition of the claw of the first hind-toe, resembles Tamias in the slender form of the body, but displays great variation in the length of the tail, which may be a mere stump, or comparatively long.
It is a large rodent known to the Tupi Indians as the paca-rana, or false paca, in allusion to the resemblance of its coloration to that of the true paca, from which it differs by its elldeveloped tail, the absence of cheek-pouches, the full development of all five toes and the wider thorax.
Both first and second compartments are remarkable for the presence of a number of pouches or cells in their walls, with muscular partitions, and a sphincter-like arrangement of their orifices, by which they can be shut off from the rest of the cavity, and into which the fluid portion only of the contents of the stomach is allowed to enter.
These monkeys are characterized by their lank bodies, long slender limbs and tail, welldeveloped thumbs, absence of cheek-pouches, and complex stomachs.
Branchiostoma Costa, having paired sexual organs (gonadic pouches); 2.
At the top of each of these pouches there is a minute orifice, the aperture of a small tubule lying above each pouch in the dorsal coelom.
At the level of its posterior end a pair of funnel-shaped pouches of the atrium are produced forwards into the dorsal coelom.
==Reproductive System== The sexes are separate, and the male or female gonads, which are exactly similar in outward appearance, occur as a series of gonadic pouches projecting into the atrial cavity at the base of the myotomes (figs.
At the breeding season the walls of the pouches burst and the sexual elements pass into the atrium, whence they are discharged through the atriopore into the water, where fertilization takes place.
(Adapted from Hatschek.) pc, Praechordal head-cavity of embryo; cc, collar-cavity (first somite); my, mesodermic somites (myocoelomic or archenteric pouches); ch, notochord with the neural tube (neurochord) lying upon it; np, anterior neuropore; ne, position of posterior neurenteric canal.
The eight adradial gonads on the subumbral walls of the four radial pouches, representing primitively four horse-shoeshaped gonads each divided into two by an interradial septum.
A similar condition is seen in Pelagia, where the number of gastric pouches is increased to sixteen.
Shoe-shaped gonads (ov) mark, Oral arms. ing four stomach-pouches, b t tentacles.
Stomach or its pouches arise gv, Radiating and anastomosing sixteen radial canals, four canals of the enteric system.
Enteric pouch of the umbrella, in the left-hand figure, points to the cavity uniting neighbouring pouches near the margin of the umbrella and giving origin to TCa, the tentacular canal.
The stomach has sixteen marginal pouches and the general anatomical structure recalls that of Pelagia.
- Medusae more or less cubical in form, with four perradial rhopalia alternating with four interradial tentacles or groups of tentacles; oral arms short; stomach a wide cavity bearing four interradial groups of phacellae and giving off four broad perradial pouches completely separated from each other by four interradial septa (i.e.
We may, with Sedgwick, suppose the coelom to have originated by the enlargement and separation of pouches that pressed outwards from the archenteron into the thickened body-wall (such structures as the genital pouches of some Coelentera, not yet shut off from the rest of the cavity), and they would probably have been four in number and radially disposed about the central cavity.
We further suppose that of the four coelomic pouches one was in front of the mouth, one behind the anus, and one on each side.
The comparative anatomy of living forms, combined with the evolutionary hypothesis sketched above, suggests that the early holothurians possessed the following characters: subvective grooves entirely closed; 5 radial canals, proceeding from the water-ring, gave off branches furnished with ampullae to the podia on each side of them, the 10 anterior podia being changed into cylindrical tentacles; the transverse muscles of the body-wall formed a circular layer, probably interrupted at the radii (though Ludwig believes the contrary); longitudinal muscles as paired radial bands, without those special retractors for withdrawing the anterior part of the body which occur in many recent forms; a hydropore connected with the water-ring by a canal in the dorsal mesentery; a gonopore behind the hydropore connected by a single duct with a bunch of genital pouches on each side of the mesentery; gut dextrally coiled, with a simple blood-vascular system, and with an enlargement at the anus for respiration, this eventually producing branched caeca called "respiratory trees"; skeleton reduced to a ring of 5 radial and 5 interradial plates round the gullet, and small plates, with a hexagonally meshed network, dispersed through the integument.
They have large cheek-pouches, large naked callosities, often brightly coloured, on the buttocks, and short thick limbs, adapted rather to walking than to climbing.
Many of the species have medium or even long tails, while some are nearly double the size of the typical representative of the group. All, however, have large cheek-pouches, whence the name of pouched marmots, by which they are sometimes called; and they have the first fronttoe rudimentary, as in marmots.
The officers buttoned up their coats, buckled on their swords and pouches, and moved along the ranks shouting.
Their abdominal bones are like those of the marsupials; and they are furnished with pouches for their young, but have no teats, the milk being distilled into their pouches from the mammary glands.
The radial canals are represented by wide gastric pouches, and may be absent, so that the tentacles arise directly from the stomach (Solmaridae).
