Ant colonies > Internal structure of ants > Glandular system

Glandular system

The Glandular System

Glands are well-developed in ants, and, owing to their importance in the ethological relations of these insects, deserve particular notice.

The following groups may be distinguished:

1. Integumentary glands, arising in the embryo, larva or pupa as invaginations of the ectodermal cell-layer (hypodermis), and including the antennary, mandibular, maxillary, labial and metasternal glands, those of the sixth abdominal (third or fourth gastric) segment, and of the fore metatarsus. Here, too, may be included the unicellular glands connected with the olfactory and tactile organs, to be considered in the next chapter. All the integumentary glands are present in the male as well as in the worker and female ant.

2. Reproductive glands, including the penial glands of the male, and in the worker and female the homologous glands of the sting-sheath, belonging to the ninth abdominal (sixth or the poison, accessory and repugnatorial, or anal glands of the worker and female, and the glands of the seminal vesicle of the male.

3. Glands of the alimentary canal. These comprise the post-pharyngeal, ventricular and rectal glands and the Malpighian vessels.

4. Glands of the circulatory system, including the aenocytes, pericardial cells and adipocytes, or fat body. These, unlike the three other categories of glands, are ductless.

The glands of the alimentary tract have been briefly described, and those of the circulatory and reproductive systems will be taken up later, so that here are only integumentary glands will be considered.

Fig, 17. Frontal section of head of Myrmica levinodis worker. (Janet.) cc, Central body of brain; cp, pedunculate bodies; ol, optic lobe; on, optic nerve; e, eye; lo, olfactory lobe with glomeruli ; mg, mandibular gland; rs, reservoir; cr, cribellum ; d, ducts from gland cells; tr, tracheae; mx, maxillary gland; lbr, labrum ; mc, buccal cavity.

The antennary glands consist of a few isolated cells with slender ducts opening on a small area in a depression at the base of each antenna. The mandibular glands (Fig. y, mg) are well-developed and comprise a large cluster of cells in each side of the head just in front of the optic ganglia. Their ducts, grouped in bundles, but not uniting, open separately on a cribellum, or sieve-like plate on the thin wall of a larger cavity, which narrows anteriorly and opens as a small slit at the base and near the upper surface of the mandible. The maxillary glands (mx) consist of two groups of cells near the median sagittal plane of the head, above the buccal tube and near the inf rabuccal pocket.

Their separate ducts open on each side on a cribellum in the lateral wall of the buccal tube. The labial, usually ~called the salivary glands, are paired, like the preceding, but are situated in the thorax. Their duct, however, is unpaired and openson the labium. These glands are derived from the spinning glands, or sericteries of the larva. In Formica rufa, according to Meinert, each of the lateral ducts, before uniting with its fellow to form the unpaired terminal duct, becomes inflated and functions as a receptaculum for the glandular secretion.

The metasternal glands (Fig. 18), whichwere first seen by Meinert and Lubbock, have been carefully investigated by Janet. He regards them as belonging to the epinotum and calls them "glands de 1'anneau mediaire," but Emery asserts positively that they belong to the metasternal or ventral pieces of the third thoracic instead of to the epinotal, or first abdominal segment. In Myrmica rubra, according to Janet, "the fine ducts of the numerous gland cells unite in a large bundle and open separately on a depressed cribellum, situated on the ceiling of a large chamber formed by an invagination of the chitinous exoskeleton.

From near the surface perforated by the orifices of the secretory ducts, seven or eight little chitinous folds arise and extend laterally along the walls of the chamber. These folds, which form small projecting ridges, soon unite in two groups which border a small gutter on a slight eminence. Towards the ventral region all traces of the ridges disappear

FIG. 18. Section of metasternal gland of Lnsius flavus. (Janet.) a, Orifice of episternal chamber ; b, hairs guarding orifice; c, cribellum ; d, gland_ cells ; e, ducts of same ; f, trichodes projecting into episternal chamber ; g, ganglion.

, but the gutter, reduced to a simple depression of the wall, is continued very distinctly to the slit which forms the opening of the chamber. This latter is always filled with air." In Lasius flavus "the chamber is widely open to the exterior and the grooves of its walls are absent and replaced by hairs." In one of his preparations Janet found that " these hairs are inserted inside the chamber around the cribellum and converge in such a way as to appear like a pointed, hollow brush, i. e., one reduced to the hairs that form its external surface. This pencil recalls the trichodes of myrmecophilous beetles. In Fomica rufa the chamber is much reduced and opens more widely to the exterior than in Lasius flavus. The cribellum is beset with hairs which form a brush long enough to project outside the chamber. The glands of the sixth abdominal segment consist of two small clusters of cells whose ducts open on the dorsal intersegmental membrane just in front of the rigid chitinous border of the seventh segment. The metatarsal gland is situated in the fore-leg at the base of the tarsal comb of the strigil.