Landois and Sharp, i. e., at the base of the first gastric segment, and also on the corresponding part of the postpetiole. These two segments certainly admit of the greatest amplitude and freedom of movement and are, therefore, the most favorable spots for the development of organs like those under discussion. In Myrmica rubra there are more than 50 ridges to the postpetiolar file, but in the organ at the base of the gaster there are more than 130 and these are much finer. The ridges, however, are twice as broad in the anterior as they are in the posterior portion of the gastric file. It appears, therefore, that the most highly developed stridulatory surfaces of the Myrmicinæ and Ponerinæ are not strictly homologous, since in the former subfamily the principal organ is situated on the third abdominal, whereas the only stridulatory file of the latter is on the second abdominal segment. In both cases, however, the main organ is at the base of the first gastric segment. What seem to be incipient stages in the development of the organ from ordinary polygonal asperities of the chitinous integument, are seen in the Dorylinæ. Of the first gastric segment in one genus of this subfamily Sharp says: "I have examined workers of several species of Eciton, and find that they have no stridulatory organ, the sculpture being uniform all over the dorsum of the neck of the segment." My own observations on the workers of several species of Eciton, Enictus. Dorylus and Cheliomyrmex confirm this statement. In all these genera the neck of the postpetiole and that of the first gastric segment are covered with polygonal asperities, but these are much more conspicuous than on other portions of the segments, and in one species (Eciton opacithorax) they are transversely lengthened in the mid-dorsal region so that they foreshadow the file ridges of the Ponerinæ and Myrmicinæ.

Although the number of segments in the gaster is morphologically eight, when the pedicel consists of a single segment, and seven when it consists of two, only four segments are externally visible in the worker. and female and five in the male. The remaining segments are very small and telescoped into the larger ones in front of them. Tracheal stigmata are present on the eight basal abdominal segments, i. e., on the epinotum, pedicel and the five or six basal gastric segments.

The terminal segments in the female and worker may bear a sting. which is of considerable interest, because it can be traced back to its primitive homologue, the ovipositor. In many Orthoptera, like the katydids and crickets, this organ consists of three pairs of appendages, which, as I have shown (1893), are the modified embryonic legs of the eighth, ninth and tenth abdominal segments. Owing to a very early embryonic fusion of their corresponding segments the pair belonging to the tenth segment moves up and comes to lie between the ninth pair, so

that the ninth segment appears to bear two pairs of appendages. In the Hymenoptera the ovipositor is still retained with its Orthopteroid function in certain families like the ichneumons and gall-flies, which oviposit in the tissues of insects and plants. In the bees, wasps and ants, however, the organ has lost this primitive function and has become an organ of defence. Its embryological origin in these forms, however, is the same as in the Orthoptera. Dissections of the sting of the pupal and adult ant show that the pairs of appendages become closely applied to one another so that they appear as a single organ. The appendages of the tenth segment actually fuse to form a single, pointed, grooved piece, the gorgeret (Stachelrinne) which encloses the pair of appendages belonging to the eighth segment. These are very slender and pointed and are known as the stylets, or prickles (Stechborsten). The appendages of the ninth segment become somewhat lamelliform and, without fusing with each other, enclose the gorgeret as the sting-sheath (Stachelschiede). In stinging, the pointed gorgeret is thrust into the skin and then the stylets are alternately pushed deeper into the wound beyond the tip of the gorgeret which they do not surpass when the sting is at rest. The duct of the gland that supplies the poison, which produces the burning sensation, enters the base of the gorgeret. The stylets are smooth and not barbed on their sides as they are in the bee; hence the ant is able to withdraw its sting from the wound. While the sting is very large and well-developed in the Ponerinæ, Doryline and most Myrmicinæ, it is vestigial or absent in the other subfamilies.

At the tip of the male gaster there are three pairs of rather complicated appendages forming the genital armature. They are developed on the ninth abdominal segment, i. e., the segment which in the female gives rise to the sting sheath. The sternal plate of this segment, which in the male lies in front of the appendages, is known as the annular lamina (Fig. 19, la). The three pairs of appendages enclose one another, so that we may distinguish an outermost, a median and an innermost pair. The outermost pair has been called the stipites (st). The median pair is sometimes more or less completely divided into two pairs, known as the volsellæ (v) and lacinia respectively; and the whole group of appendages comprising the stipites, volsellæ and laciniæ are known as the external paramera (Verhöff and Emery). The innermost pair alone is known as the internal paramera. They are closely applied to each other in the median sagittal plane of the body and function as a penis (p). During copulation the stipites. which are large, robust and often covered with hairs, function as claspers. The volsellæ and laciniæ, which are smaller and less heavily

chitinized and furnished with numerous tactile sense organs, in all probability also have a clasping function. The inner paramera are very delicate. In some ants they have serrated edges which probably serve to hold them in place in the vagina of the female. In addition to the genital valves there is a pair of small, hairy appendages, the penicilli, attached to the tergite, or dorsal plate of the tenth abdominal segment. There can be little doubt that these represent the cerci of Blattoid and other primitive insects and must therefore belong to the anal or eleventh abdominal segment. The presence or absence of the penicilli and the conformation, permanent retraction or protrusion of the different paramera are used in classification as valuable diagnostic characters. Although we may be tempted to homologize the three pairs of male genital appendages with the three pairs of appendages which go to form the sting in the female, it is very doubtful whether more than one of these pairs, the stipites, develop from rudiments of the embryonic walking limbs. If this is true, the stipites correspond with the pair of appendages of the ninth segment in the female, which give rise to the sting sheath, and the volsellæ, laciniæ and penis are merely differentiations of the median portion of the ninth sternite.

CHAPTER III.

THE INTERNAL STRUCTURE OF ANTS.

"In his tam parvis, atque tam nullis, quæ ratio, quanta vis, quæ inextricabilis perfectio!"-Pliny, “Historia Animalium," XI, 2.

The Alimentary Tract.-This extends the entire length of the body from the mouth to the anus as a tube with but a slight tendency to convolution in the gaster. The walls of this tube are curiously modified in different portions of its length, so that we can recognize a number of regions known as the infrabuccal chamber, buccal tube, pharynx, œsophagus, crop, proventriculus, stomach, small intestine and rectum. The shape and extent of these regions are indicated in the accompanying diagram taken from Janet (Fig. 13). Owing to the volume of the brain and cephalic glands, to the narrowness of the thorax and pedicel in the worker, and the great development of the wing muscles and glands in

FIG. 13. Sagittal section of worker Myrmica rubra. (Janet.) t, Tongue; lbr, labrum; clp, clypeus; sg, opening of salivary gland; bo, mouth opening; hp, infrabuccal chamber; ph, pharynx; phg, pharyngeal glands; oe, oesophagus; cr, crop; gz, gizzard; st, stomach; lin, large intestine; mp, Malpighian vessels; rc, rectum; rcg, rectal gland; an, anus; fgl, frontal ganglion; rec, recurrent nerve; br, brain; mdg, mandibular ganglion; mrg, maxillary ganglion; lg, labial ganglion; soe, subœsophageal ganglion; cho, prothoracic chordotonal organ; thg', thg2, thg3, pro-meso- and metathoracic ganglia; ag'-ag2, ag, 8-11, first to eleventh abdominal ganglia; sym, sympathetic connective, running along œsophagus to prestomachal ganglion (stg); st, sting; vg, vagina; ten, tentorium in section.

the thorax of the male and female, the alimentary canal is cramped for space and hence very tenuous, except in the gaster, where its most important parts are situated. The mouth opening, which, as we have

seen, is bounded above by the labrum and clypeus, on the sides by the maxillæ, and below by the protrusible tongue, leads into a short, compressed buccal tube, dilated ventrally to form a spheroidal sac, the infrabuccal cavity or chamber (hp). This chamber is of great importance to the ant as a receptacle both for the fine particles of solid and semisolid food rasped off or licked up by the tongue, and for the foreign matter scraped from the surfaces of the body by this organ and the strigils. Any juices that may be contained in the substance are sucked

C

FIG. 14. Pellets or castings from the infrabuccal chamber of Formica rufa, enlarged. (Janet.)

back through the pharynx into the crop and the useless solid residuum is eventually thrown out as a little body which preserves the form of the chamber in which it was moulded. Such bodies, called by Janet "corpuscles de nettoyage," are often seen scattered about the floors of artificial nests after the ants have been fed on starchy substances or after their bodies have been dusted with plaster of paris (Fig. 14). The short buccal cavity is continued back into the muscular pharynx which narrows still further to form the long œsophagus traversing as a slender tube the head, thorax and pedicel (Fig. 13, oe).

The buccal tube, which, according to Janet, "has a protractor and a retractor muscle, is provided with soft lips that can be applied to the surface of the substances previously rasped off by means of the tongue for the purpose of obtaining any liquid they may contain. Transverse scale-like folds with their points turned outward line the walls of the buccal tube and serve to retain any solid particles not sufficiently minute."

"The pharynx is a flattened cavity the dorsal and ventral walls of which are moved by powerful dilator muscles. Behind it is furnished with two expansions arising laterally and united at their tips by a transverse constrictor muscle. During aspiration the pharynx, through the action of its dilators and a kind of posterior sphincter, opens in front and closes behind. In swallowing there is first produced a steelyard-like movement of the dorsal wall, whereupon the pharynx is opened behind, while the buccal tube is closed in front. Then, owing to the action of the transverse constrictor, the dorsal approaches the ventral wall from before backward. The two walls thus come in contact with each other and the liquid which was contained in the pharynx is pushed into the œsophagus." Immediately behind the pharynx two groups of finger-shaped post-pharyngeal glands open by a pair of orifices into the alimentary tract (Fig. 13, phg).