ANTS.

comprising an unpaired upper lip, or labrum, the mandibles, maxillæ and labium, or lower lip. In the last the originally separate and paired embryonic appendages are fused in the median line so that they form a continuous floor for the mouth or buccal cavity. In the cranium the following regions may be distinguished: the front, a region bounded. anteriorly by the posterior edge of the clypeus and laterally by a pair

FIG. 4. External structure of head in Myrmica rubra worker. (Janet.) A, Dorsal aspect of head; B, anterior aspect; a, mandible; b, clypeus; c, frontal area; d, frontal groove; e, frontal carina; f, vertex; g, occiput; h, temple; i, base of antennal scape; k, cheek; 1, eye; m, lateral ocellus; n, median ocellus; o, tentorial pit; p, labrum; q, labium; r, maxilla; s, maxillary palp; t, labial palp; u, gula.

of ridges, the frontal carinæ or laminæ, just mesial to the insertions of the antennæ. A small, usually triangular, median region. the frontal area, can be easily seen in the middle line just back of the clypeus, and often there is an impressed line, the frontal groove, extending back from this area over the middle of the front. The frontal region passes without definite boundary into the vertex and temples, the former extending posteriorly, the latter lying above and behind the eyes. The short region between the vertex and the narrow opening, or foramen through which the alimentary tract and nervous system pass into the thorax, may be called the occiput. The cheeks, or genæ, comprise the portions of the cranium anterior to the eyes and lateral to the frontal carinæ. The ventral portion of the head, bounded in front by the labium, on the sides by the cheeks and extending to the occipital foramen, is the throat, or gula. It is well-developed in the ants and is usually divided into two equal halves by a longitudinal suture.

The mandibles, being the parts with which the ant comes into most effective relations with its environment, present, like the beaks of birds and the teeth of mammals, a bewildering variety of structure (Fig. 3).

A

b

a

They are used for excavating soil or wood, cutting up the food, fighting, carrying the prey, their young or one another, and in some species, even in leaping by closing them rapidly against hard bodies. Ants are remarkable in being able to open and close their mandibles independently of the maxillæ and labium. These organs, which lie underneath the small and vestigial labrum and close the mouth completely except when the insect is feeding, have a complicated and interesting structure. The maxillæ (Fig. 5, B, D) are paired and each consists of the following pieces, or sclerites: the hinge (cardo), the stem (stipes), the maxillary palp, which may be from. 1-6-jointed, an inner blade (lacinia) and an outer blade, the galea. The galea bears a row of gustatory papillæ and a row of bristles which are used in cleaning the legs and antennæ. The lacinia is membraneous and toothless and shows that the ant feeds on liquid substances only. This is also proved by the structure of the labium (Fig. 5, C), which consists of the following sclerites: the hind chin (submentum), the chin (mentum) and the tongue (glossa), al! unpaired, and the labial palpi, consisting of from one to four joints, the paraglossæ and hypopharynx, which are paired. The tongue, with which the ant rasps off or laps up its liquid or semi-liquid food, and cleans itself and its fellows, is a protrusible, elliptical pad, covered with fine transverse ridges. At its base lies the opening of the salivary duct. The paraglossæ are small sclerites beset with rows of bristles. The hypopharynx, which is less developed than in some of the other

B

m

D

FIG. 5. Mouthparts of Myrmica rubra. (Janet.) A, Seen from the lower, or ventral side, in situ; B and D, maxillæ; C, labium, seen from the upper, or dorsal side, detached; a, mandible; b, maxilla; c, mentum; d, maxillary palp; e, labial palp; f, glossa, or tongue; g, adductor muscle of mandible; h, abductor muscle of mandible; i, labium; k, gustatory organs; 1, duct of salivary glands; m, maxillary comb; n, gular apodeme.

Hymenoptera, such as the wasps, covers the mentum and paraglossæ. Its upper portion is somewhat lobed and bears two rows of backwardly directed bristles, which form a V and seem to be used for holding the food fast in the mouth. The upper lip, or labrum, forms the roof of the mouth. It is poorly developed and consists of a bilobed plate hidden beneath the anterior border of the clypeus (Fig. 4, Bp).

The antennæ are far and away the most important sense organs of the ant. They are inserted in sockets on each side of the frontal carinæ, and consist of a series of joints of variable number and length. The lowest number, four, is found in the genus Epitritus (Fig. 75); the greatest, thirteen, in the males of many of our common ants. Usually the males have one more joint than the females and workers. The first joint, known as the scape, is always considerably elongated, except in the males of some species. The remainder of the antenna, the funiculus, consists of very much shorter joints, the articulations between which are less movable than that between the scape and funiculus. This latter articulation is of such a nature that the funiculus can be folded up against the scape producing the peculiar Formicid elbow in the antenna, and both this and the socket articulation at the insertion of the scape permit extraordinary freedom in the movements of the appendage. The funiculus may be of nearly uniform diameter throughout, with very similar joints, or from one to four of the terminal joints may be thickened and elongated and thus constitute a club.

Ants have two kinds of eyes: the compound, lateral eyes, two in number and placed on the sides of the head (Fig. 4, 1), and the simple, median eyes, ocelli, or stemmata, of which there are three on the vertex (Fig. 4, m, n). Both kinds are best developed in the males, less in the females and least in the workers, which often lack the stemmata altogether. In addition to these great differences, which are constant. in the three phases of nearly all species, there are considerable differences in the development of the eyes in the different genera. A more detailed account of these organs and the antennal sense organs is given in Chapter IV.

The Thorax.-Owing to the fusion of the first abdominal segment of the embryo and larva with the hindermost portion of the thorax during pupation, the thorax of the adult ant may be said to consist of four segments, a pro-, meso- and meta-thoracic and a mediary segment, or epinotum. In our description we may follow Emery (1900d) who has carefully studied the external morphology and reviewed the nomenclature of these four segments in the male, female and worker. The primitive condition of the thoracic region may be readily traced through the ergatoid females and workers of these forms to the much reduced

and specialized condition in the workers of more highly developed ants like the Camponotinæ.

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FIG. 6. Thorax of a male Ponerine ant, Streblognathus æthiopicus in profile. (Emery.) a' and a2, Anterior and posterior wings; em and em', meso- and metathoracic epimera; es and es', episternites of the same segments; epn, epinotum; g, metasternal gland; mtn, metanotum; pet, petiole; ppet, postpetiole; pn, pronotum; ppt, parapteron; sc, scutum of mesonotum; sct, scutellum; st and st', meso- and metathoracic sternites; stg', stg2, stg and stg', stigmata of meso- and metathorax, epinotum and petiole. The parts of the prothorax are shaded with broken lines, those of the mesothorax, epinotum and petiole are unshaded, those of the metathorax are shaded with unbroken lines; the wing articulations are dotted.

Emery starts with a primitive form like the male Streblognathus ethiopicus (Fig. 6). In this insect the various elements or sclerites of which the thorax is composed are clearly delimited by sutures. The prothorax is very small and consists dorsally and laterally almost entirely of the unpaired pronotum, with a slender ventral element, the prosternum, to which the coxa of the fore-leg is articulated. Owing to the development of the wings, the mesoand metathorax are much larger. The former is especially well-developed, in correlation with the larger size of the fore wings, and comprises dorsally a large unpaired, convex plate, the mesonotum; ventrally on each side, and articulated below with the coxa of the middle leg, is the mesosternum, which also forms much of the pleural wall of the thorax. The space on each side between the mesonotum and the mesosternum is occupied by a pair of elements, one of which, the mesepisternum, is ventral; the other, the mesepimeron, dorsal. The fore-wing is articulated just above the mesepimeron and below a small sclerite, which is behind the mesonotum and may be called the mesoparapteron, or præscutellum. The insertion of the forewing is covered by a small chitinous scale, the tegula. Viewed from above the large mesonotum in some male ants presents a Y-shaped groove, known as the Mayrian furrow (Fig. 7, sM). Each side of the mesonotum is marked off for some distance from the median portion of the segment by a distinct suture, which may be called the parapsidal suture. The area thus cut off on each side is the parapsis. The sides and the ventral portions of the metathoracic segment are similar to those of the mesothorax, but smaller. It is possible to distinguish a metasternum, to which the coxa of the hind-leg is articulated, a metepisternum and a metepimeron. Dorsally, however, the metano

tum, which, of course, is serially homologous with the mesonotum, is very narrow antero-posteriorly and separated from the mesonotum by a large, unpaired, semi-circular element, the scutellum. Between the scutellum and metanotum, a small piece, the metaparapteron, or postscutellum, is intercalated on each side. The hind-wing is inserted

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FIG. 7. Dorsal aspect of

thorax of male Ponerine ant, Paraponera clavata. (Emery.) a' and a2, Anterior and posterior wings; pn, pronotum; sc, scutum of mesonotum; SM, Mayrian furrow; pss, parapsidal furrow; pps, parapsis; teg, tegula; ppt and ppt, paraptera of meso- and metathorax; sct, scutellum; min, metanotum; epn, epinotum; pet, petiole.

between this metaparapteron and the metepimeron. The epinotum, which, as we have seen, is morphologically the first abdominal segment, is large and convex and in many ants furnished with a pair of stout spines or teeth. It is closely applied to the metathorax from the posterior edge of the mesonotum above to the ventral edge of the metathorax below.

The thorax has on each side three openings, or stigmata, to the respiratory tubes, or tracheæ. The first, belonging morphologically to the mesothorax. lies beneath a small flap-like expansion of the pronotum where it abuts on the mesepimeron. The second or metathoracic stigmata lies beneath the insertion of the hind-wing and near the posterior end of the mesepimeron. The third stigma, belonging to the first abdominal segment, is distinctly seen on the side of the epinotum.

In the female ant (Fig. 8, A) the thorax is constructed on the same plan as that of the male, but is more robust and lacks the Mayrian furrow, which is also absent in the males of many genera. The males and females of most species, however, exhibit a greater simplification of the pleural region of the thorax, owing to the fusion of the epimera and episterna with each other and often also with the sterna in the meso- and metathorax, and a very intimate fusion of the epinotum with the latter segment.

Turning to the workers, which are wingless, there is noticeable a great reduction in the size of the meso- and metathorax plus the epinotum, so that the three divisions of the thorax are more nearly of uniform size (Fig. 8, C, Fig. 9, a). In certain species, and especially in the ergatoid females (Fig. 8, B) and soldiers of a few genera, the various dorsal elements, such as the paraptera, scutellum and meta