Marsupials may be defined as viviparous (that is non-egglaying) mammals, in which the young are born in an imperfect condition, and almost immediately attached to the teats of the mammary glands; the latter being generally enclosed in a pouch, and the front edge of the pelvis being always furnished with epipubic or "marsupial" bones.
Further, it is considered that too much weight has been assigned to the characters distinguishing monotremes from other mammals, foetal marsupials showing a monotreme type of coracoid, while it is probable that in the long run it will be found impossible to maintain the essential dissimilarity between the milk-glands of monotremes and other mammals.
Bancrofti is known to live in the lymphatic glands, and its embryos Microfilaria sanguinis hominis nocturna, passing by the thoracic duct, reach the blood-vessels and circulate in the blood.
Insects are attracted to the mouth of the pitcher by a series of glands, yielding a sweet excretion, which occurs on the stem and also on the leaf from the base of the leaf-stalk to the lid and peristome.
Embedded in the incurved margin of the rim which affords a very insecure foothold to insects, are a number of large glands excreting a sweet juice.
The cavity of the pitcher is in some species lined throughout with a smooth glistening surface over which glands are uniformly distributed; these glands secrete a liquid which is found in the pitcher even in the young state while it is still hermetically closed by the lid.
Other species the glands are confined to the lower portion of the cavity surface, while the upper part bear a smooth waxy secretion on which it is impossible, or at any rate extremely difficult, for insects to secure a foothold.
Insects, especially running insects, which have followed the track of honey glands upwards from the stem along the leaf, reach the mouth of the pitcher, and in their efforts to sip the attractive marginal glands fall over into the liquid.
The surface of the leaf, especially the laminar wing, bears glands which in spring exude large glistening dr„ r, s of nectar.
Then come the glandular surface (C), which is formed of smooth polished epidermis with numerous glands that secrete the fluid contents of the pitcher, and finally the detentive surface (D), of which the cells are produced into long and strong bristles which point A FIG.
A number of glands on the interior of the pitcher secrete a plentiful fluid which has digestive properties.
Some hydathodes are active glands, secreting the water they expel from the leaf.
Types of glands also exist, either in connection with the epidermis or not, such as nectaries, digestive glands, oil, resin and mucilage glands, &c. They serve the most various purposes in the life of the plant, but they are not of significance in relation to the primary vital activities, and cannot be dealt with in the limits of the present article.l The typical epidermis of the shoot of a land plant does not absorb water, but some plants living in situations where they cannot depend on a regular supply from the roots (e.g.
In some cases special secreting tissues, resin ducts, oil glands, laticiferous tissue, crystal sacs, &c., may be developed among the ordinary secondary vascular elements.
The glands are variable in size and position; when very large, e.g.
As these possess no glands they are a worthless substitute.
The glands occur in groups, and lead into common ducts which open usually so much reduced that the foremost apparent ventral sclerite of the abdomen represents the third sternite.
Sometimes the glands are found beneath the disk of the elytron, opening by pores on the surface.
Many beetles have, in connexion with the anus, glands which secrete a repellent acid fluid, serving as a defence for the insect when attacked.
Many of the Hydrophilidae construct, for the protection of their eggs, a cocoon formed of a silky material derived from glands opening at the tip of the abdomen.
But there are several subfamilies of ants whose females have the lancets of the sting useless for piercing, although the poison-glands are functional, their secretion being ejected by the insect, when occasion may arise, from the greatly enlarged reservoir, the reduced sting acting as a squirt.
In the case of many Oligochaeta where there is no vascular network surrounding the nephridium, this function must be the chief one of those glands, the more elaborate process of excretion taking place in the case of nephridia surrounded by a rich plexus of blood capillaries.
Alimentary canal rarely coiled, occasionally with glands which are simple caeca and sometimes serve as air reservoirs; jaws often present and an eversible pharynx.
Alimentary canal straight, often with appended glands of complicated or simpler structure; no jaws.
Associated with these glands are frequently to be found bundles or pairs of long and variously modified setae which are termed penial setae,to distinguish them from other setae sometimes but not always associated with rather similarglandswhich are found anteriorly to these, and often in the immediate neighbourhood of the spermathecae; the latter are spoken of as genital setae.
The oesophagus is often furnished with glandular diverticula, the "glands of Morren," which are often of complex structure through the folding of their walls.
- Female reproductive system plex glands appended to of Hyperiodrilus.
They open in common with, or near to, or, more rarely, into, glands which are not certainly comparable to the atria of the Limicolae.
Two osphradia present but no hypobranchial glands nor operculum.
RHIPIDOGL0ssA.-Aspidobranchia with a palliovisceral anastomosis (dialyneurous); eye-vesicle closed, with crystalline lens; ctenidia, osphradia and hypobranchial glands paired or single.
Salivary glands are present, and in some carnivorous forms (Dolium) these secrete free sulphuric acid (as much as 2% is present in the secretion), which assists the animal in boring holes by means of its FIG.
Other glands opening on or near the foot are: (I) The suprapedal gland opening in the middle line between the snout and the anterior border of the foot.
Forms and in terrestrial genera such as Cyclostoma; (2) the anterior pedal gland opening into the anterior groove of the foot, generally present in aquatic species; (3) dorsal posterior mucous glands in certain Cyclostomatidae.
The sexes are distinct, as in all Streptoneura; and genital ducts and accessory glands and pouches are present, as in all Pectinibranchia.
On the under side of the free edge of the mantle are situated the numerous small cutaneous glands which, in the large A plysia camelus (not in other species), form the purple secretion which was known to s the ancients.
The first is flaccid and sluggish in its movements, and has not much power of contraction; its epipodial lobes are enormously developed and extend far forward along the body; it gives out when handled an abundance of purple liquid, which is derived from cutaneous glands situated on the under side of the free edge of the mantle.
Depilans; it is firm to the touch, and contracts forcibly when irritated; the secretion of the mantle-glands is not abundant, and is milky white in appearance.
The alimentary canal commences with the usual buccal mass; the lips are cartilaginous, but not armed with horny jaws, though these are common in other Opisthobranchs; the lingual ribbon is multidenticulate, and a pair of salivary glands pour in their secretion.
Accessory glands and The generative organs lie close to the ducts of Aplysia.
They are not merely digestive glands, but are sufficiently wide to act as receptacles of food, and in them the digestion of food proceeds just as in the axial portion of the canal.
Digitate accessory glands on the female duct.
Some of these glands may be modified for special purposes - as silk-producing glands in caterpillars or as poisonglands in blood-sucking flies and bugs.
S, Salivary glands and reservoir.
- Ovaries of Cockroach, with Oviducts Od and Colleterial Glands CG.
Accessory glands are commonly present in connexion both with the male and the female reproductive organs.
The poison-glands of the sting in wasps and bees are well-known examples of these.
Following the chronological order we are here adopting, we next have to recur to the labours of Nitzsch, who, in 1820, in a treatise on the nasal glands of birds - a subject that Nitzsch had already attracted the attention of Jacobson (Nouv.
It is probably owing to the possession of such glands and the varied purposes for which the silk is used that spiders as a group far surpass the other orders of Arachnida, with the possible exception of the Acari (mites and ticks), in diversity of form and of size, in numbers of genera and species, in extent of geographical distribution, and in adaptation to varied habitats.
Their success in the struggle for existence, as already indicated, must be assigned in a great measure to the possession of silk glands and to their power of manipulating the silk for a variety of purposes.
Dictyna may be cited as an example of a group of spiders, sometimes called the Cribellata, which have certain spinning glands and appliances not possessed by others.