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lars obliquely downward through the cranial cavity (Fig. 2, MC). These mesocephalic pillars are inserted in the floor of the skull just at the sides of the occipital foramen (FO).

BR

MX

FIG. 2.-Lateral view of bee's skull. FO, OC

AT, root of antennæ;

BR, basi-suspensorium;
MR, medi-suspensorium;

Thus the endocranium consists of a pair of pillars, arising by strong roots from the cranial floor, and fixed above to the clypeus. (The clypeus has to support the mandibles and to cipital foramen; MC, afford attachment to many muscles.) Near mesocephalic pillars; the top each pillar is forked transversely so as to afford more extensive support. (Fig. 3, MC.) It is these pillars which render a bee's head so strong, though its shell is rather thin. The mesocephalic pillars of an ant's skull are similar to those of the bee; and we observed short tendons in the neck serving to antagonize them.

BL, basi-labium; MX, maxilla; MD, mandible.

transverse sec

The pillars ascend in front of the cerebral brainlobes, running between them and the ophthalmic lobes, and keep the large ocular apparatus in its FIG. 3.- Diaproper place. grammatic view Burmeister's well-known account of the endo- of bee's skull in cranium of insects has many errors. He represents tion. References that of Hymenoptera as rising from the base and as in Fig. 2. ending in two points; he seems to have broken off the pillars and so missed their attachment to the clypeus. He says that Diptera and Hemiptera have no endocranium. This is partially true of the Muscida; but we have shown1 that in all probability the basal part of the proboscis of these insects represents the endocranium, and there is a rudiment of the endocranial roots in a small bridge across the occipital foramen. In the large gadfly (Tabanus atratus), and in the mosquito, we find cephalic pillars as in the bee (besides what seems to be a splachnodeme or pharynxcase supporting the complex oral armature.) Coreus, of Hemiptera, though seemingly devoid of mandibles, maxillæ, labium and all processes related to them, has a pair of processes depending from the clypeus, in the position of the upper part of the mesocephalic pillars. These probably support the pharynx and the roots of the long piercing bristles.

1 See AMERICAN NATURALIST, March, 1880. "On the Proboscis of the Housefly."

Burmeister attributes to Lepidoptera nothing more than a small bar across the occipital foramen. But we find (in the swallow tail, Papilio turnus) a strong sub-quadrate frame arising in front of this foramen, and reaching forward so as to be fixed near the roots of the proboscis.

That the mesocranial pillars represent involutions of the outer walls, may be understood from the trunk of the cray-fish, where (as Mr. Huxley has well shown) the ingrowths become plates or ridges, or even pillars. But we find a closer illustration in the heads of some other insects. Cicada has similar pillars with the bee, somewhat flattened out and attached to the sides of the head (the eyes here not reaching so far forward). This would indicate that in the bee the ridges have been displaced inwards by the encroaching of the eyes. (The clypeus of Cicada is transversely barred so as to show about ten pseudo-somites. It is easy to examine these parts from one of its exuviated shells.)

The dragon-fly has a stout ridge below the occipital foramen, sending up processes to the clypeal region, as in the bee. But these processes are broadened out and transparent, and not rigid. The clypeus itself is soft and swollen, and has a deep transverse ridge to meet the processes. Thus the large, weak cranial wall is somewhat but slightly strengthened.

The attempt to correlate the parts of the bee's head with those of the head of the cockroach, gave rise to some interesting revelations. Here Huxley's excellent description of the cockroach ("Anatomy of the Invertebrated Animals") was in good season, but we soon found that his work was superficial and faulty on this part. He states that the endocranium of the cockroach "extends as a cruciform partition from the inner face of the lateral walls of the cranium to the sides of the occipital foramen;" and speaks of the center of the cross as being “pierced by a rounded aperture through which the œsophageal nerve-collars pass." In fact, it is not cruciate in form, but consists of two pillars as in the bee (only softer), and united by membrane some way up, i. e., crotch-webbed like the webbed fingers of a water-fowl. The upper band running across is a fascia binding the two mandibles together (present in the bee, though not thus united with the mesocephalic rods). Thus we have a "tentorium," or mesocephalic plate, forming a thin diaphragm across the middle of the cranial cavity, with thickened borders in front and laterally, and itself concave up

wards so as to form a channel for the pharynx (Fig. 6, Ec). Its perforation is not as in the axis of a cross, but forwards, as if the webbing had ceased at this part. Its correspondence with the parts already described in other insects is easily shown. In the locust the lateral pillars approach more closely, so as to resemble the letter X, but the foramen and other parts are much as in the cockroach.

The Coleoptera appear to want this system. But in following out the relations of the parts I came to a view which, if correct, would explain the anomaly, and which I shall reserve for a later part of this paper.

B. Maxillary suspensorium.-It is convenient to examine together the proximal adjustments of both maxillæ and labium (or first and second maxillæ, as they may be called). These are intimately connected in their mode of attachment in all insects possessed of such parts. In the case of the bee they are strung upon a long framework with elbows and hinges, which is able to thrust them out and to draw them in. Of this framework, which we shall call the "maxillary suspensorium," we have not been able to find any satisfactory description or figure. Schmarda's Zoology gives a correct figure of its distal part; but neither Schmarda nor Westwood nor Réaumur appears to have traced the structure to its origin. The prize work on the "Anatomy and Physiology of the Bee," by M. Girdwoyn, published by Rothschild, of Paris, is grossly inaccurate at this part. We shall begin its description from its base, where it is inserted close to the inferior insertion of the mesocephalic pillars, immediately in front of the foramen magnum.

At this point there are, below the mesocephalic pillars, two basi-cranial rods, running forwards towards the oral opening (slightly ascending forwards when the mouth parts are retracted, but nearly horizontal when they are protruded). These basicranial rods arise similarly with the mesocephalic pillars; but they are united to the sides of an excavated opening in the basis cranii by a thin web, just as the mesocephalic pillars are joined to the side-wall in Cicada. They are not hinged at their root, but are firmly fixed and widen out here, and are slightly pliant, whilst their motion is limited by the web which binds them to the basi-cranial wall (Fig. 5, BR). (An engineering friend to whom we showed this structure, informed us that it involves the

principle of a machine recently patented for producing a slight and steady motion combined with strength.) The two parallel basi-cranial rods are also connected with each other by a very thin and pliable sheet of chitine, which forms the lower bounding wall of the head at the excavated part, and yet allows perfect freedom of motion to the suspensorial mechanism.

The basi-cranial rods are forked at their distal ends, where they support the maxillary rami, one at each side (Fig. 5, MR), which are joined to them by a very perfect elbow-joint, enabling the rami to fold downwards. The rami support the maxillæ, which can thus be protruded or withdrawn. We think that each of these rami corresponds with the cardo or basal segment of the maxillæ of the cockroach or beetle (though this name has been given to the process next to be described).1

The modus operandi of the maxillæ on these rami is noteworthy. Each maxilla consists of a flat base (stipe), surmounted by a lacinia resembling a knife blade, and bearing a rudimentary palp at the middle; and its lacinia can bend downwards and backwards so as to be out of the way and to present the stipe as a flat projecting plate. When the mouth parts are retracted, the two maxillæ are thus bent down, and their plate-like stipes are approximated, so as to form a hard under lip for the mouth, upon which the mandibles play in their operations (as on a piece of cork, or in cell-making as when the carpenter-bee is operating on wood). The basi and medi-labium then fill the excavated part of the basicranial surface. When the suspensorium is being protruded, the thin membrane which borders its proximal joints and which is extended so as to reach the blades of the maxillæ, becomes tense and divaricates them so as to secure their steadiness of motion and to give free play to the intervening labium.

From the distal end of the maxillary rami proceed two labial rami to support the labium, thus giving an additional joint, with a hinge which moves freely backward and forward. (This is the piece usually called cardo; we shall call it labial ramus of the suspensorium, or labi-suspensorium.) By means of it a very

1 Dr. Hagen has shown us Wolff's article on "Das Riechorgan der Biene" in Nova Acta Leop. Carol., Band xxxvIII (1875), with beautiful and accurate drawings of the structure of the bee's head. The author does not appear to have studied the parts in the relations here discussed; and he is altogether fanciful in identifying the hard parts and the muscles of the bee's skull with the bones and muscles of the mammalian head.

great degree of motion backwards and forwards is allowed to the labium, which mobility is still further increased by the protrusibility of its ligule or distal piece. The labium consists of a basal piece, usually termed submentum (we would rather call it basilabium, Fig. 5, BL); of a medial piece, usually termed mentum

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FIG. 4.

Suspensorium and mouth parts of ant. Ms, basi-suspensorium; MC, mesocephalic pillar. The other references are as in Fig. 5.

FIG. 5.-Suspensorium and mouth parts of bee. FO, Occipital foramen; BR, basisuspensorium; MR, medi-suspensorium; below BL, labi-suspensorium; to left of BL, basi-labium; ML, medi-labium; PG, paraglossæ; LP, labial palp; LG, ligule or outer tongue; MD, mandible; MX, maxilla: the terminal part of the maxilla is the lacinia, the basal part is the stipe, its narrow middle part has a rudimentary maxillary palp. One of the endocranial pillars is seen extending from beside the occipital foramen to near the insertion of the mandible.

(we would call it medi-labium, ML), and of what we may call a disti-labium, consisting of paraglossæ (PG), of well-developed labial palps (LP), and of the terminal ligule (LG), about which a great deal has been written.

In such bee-like insects as do not protrude their maxillæ, these parts are more or less simplified, so as often to illustrate and explain the complex arrangement of the bee. Very often the distal parts of the labium are reduced or condensed (so as to resemble somewhat the swollen tip of a housefly's proboscis). In Stizus grandis, with non-retractile proboscis, we found the basicranial rods to be merely a high ledge running forwards around the excavated part of the basi-cranium, and serving for insertion

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