The causes to which this singular phenomenon is ascribed are either physical or physiological.13 In order that my readers may give these views due weight, I have cited them at some length in the foot-note. My own impression is that Mr. Belt and Sir Sidney Saunders have given, between them, the true explanation of the rhythmic exhibition of light, and apart from the aesthetic realization in nature of this plan of making night glorious by the wonderful brilliancy of such insignificant objects (upon which idea this is neither the time nor the place to discourse), it is primarily a defence of the insects against danger, and is secondarily caused by that tendency to act in concert or imitation which operates upon all sentient beings. This tendency may be equally observed in a flock of sheep following its leader, a school room of hysterical girls, a political meeting, a spiritistic séance, or a hyper-sentimental religious assemblage. And I regard all these occurrences, however differing in the importance of their final results, as individual instances in a large class of similar phenomena, caused by aggregated sympathy.

I would therefore agree with Sir Sidney Saunders and Mr. Meldola in quite rejecting Mr. McLachlan's view that it is produced by a change in position of the insects caused by currents of air, or even voluntary movements in direction of flight.

To recur to the process by which the light is produced, I would add to what I have said in the beginning of this essay, that the chemical processes possible in the bodies of Lampyridæ can be scarcely if at all different from those which take place in neighborinsect rested, owing to the pubescence being then concealed; he thought this to some extent was an analogous case to that of the light of swarms of Lampyridæ." Sir Sidney Saunders observed: : "as to the contemporaneous flashes of myriads, such as are more frequently congregated on the calmest nights, surrounding objects, previously involved in obscurity, become suddenly illuminated as if by electricity, and as rapidly plunged into their antecedent gloom at alternate intervals. He could not concur in the hypothesis that currents of air had any connection with such displays or exhibitions, when not a breath was stirring around; nor that these manifestations might be evoked by sexual influences, amid vast hosts instigated to combine therein, and act in unison. He would rather attribute this phenomenon to an inherent tendency to emit their light from time to time, requiring a certain amount of repose to recruit their powers; and when any thus surcharged felt intuitively inspired to take the initiative, the others— prompted to obey a corresponding influence-followed such suggestion in responsive sequence." Ibid. p. viii. "Mr. Meldola stated that Mr. Thomas Belt (Naturalist in Nicaragua, p. 320) had expressed his belief that the luminosity of the Lampyridæ played the same part as the bright colors of many caterpillars, i. e., that it served as a danger signal, warning nocturnal foes of the inedibility of the species of this family, which he had found to be generally distasteful to birds, etc."

ing and closely allied tribes. We may therefore infer from the observations of Mr. Meldola that the ordinary metamorphoses of tissues, by the aid of some slight modification of composition and cellular structure, are capable of evolving light, which belongs to the upper end of the spectrum, such as is generally significant of the highest temperatures.

It is therefore the more extraordinary to find in these insects light of a high order not dependent on elevation of temperature, and consequent waste of energy in heat. For it must be observed, that while in one sense heat is the cause of all the phenomena we perceive, since they all have existence only within certain ranges of temperature, in another sense heat is frequently a waste product, and the only one by which the dissemination of energy occurs so as to become imperceptible.

I am aware that the sketch I have here given of the present condition of our knowledge of Lampyridæ has been written to the demonstration of my own ignorance (and that of all other students) in regard to some of the most important questions involved. But if I succeed in causing you to look upon these remarkable insects with more interest than you have previously felt, neither my time in preparing, nor your time in listening to this essay, will have been wasted.

I would especially invite the attention of the younger observers in entomology, who have to pass through the labor of patient field work and close observation of habits, before they can ascend with profit to the higher retirement of the museum and the library, to contribute more fully to our knowledge of the development and habits of the different species.

I would equally ask the attention of my colleagues, who by long training in refined experimental research are qualified for such investigations, to the solution of the physical and chemical problems suggested by the singular production of high light without heat by these animals, which are within such easy reach. And by the solution of these problems I am convinced that our knowledge of molecular physics will be increased, and our powers of theorizing less fettered by conventional ideas.

THE ENDOCRANIUM AND MAXILLARY SUSPENSORIUM OF THE BEE. By GEORGE MACLOSKIE, of Princeton, N. J.

THE аpodemes formed by an insect's crust may be either foldings outwards (exodemes), or involutions extending inwards (endodemes), or modifications of the chitinous lining of the alimentary tract (splachnodemes). Such processes are always by their nature double (including the outgoing and returning plates), and in exodemes (as the wing of a bee or the pleura of a lobster), this double nature is maintained by interposed nutritive matter (like the meat in a sandwich). In the internal foldings, however, as in the endoskeleton of insects, there is usually a complete fusion of the compound parts.

The endocranium, or endoskeleton of the head, consists of ridges, pillars, and plates, variously disposed in different orders of insects, yet adhering to a plan. Its central part when appearing as a plate is usually termed tentorium, from a fancied resemblance to the structure so named in mammals. The necessity of describing and comparing together these parts in the different groups of insects will be apparent, if we reflect that all attempts to evolve the embryology of an insect's head presuppose a knowl edge of the adult structure, inside as well as external.

210.7

The upper part of a bee's cranium consists of three pieces, epicranium (EC), clypens (c), and labrum (LR). (See fig. 1). The epicranium, or crown, extends from the occipital foramen, up the back of the head and over the vertex, to a transverse suture in front of the antennæ. It covers the whole roof and back of the head, and is medially separated in many insects (especially larvæ) into right and left divisions. It is flanked on the sides by the large compound eyes (oc); it bears at its vertex the three small eyelets; near its front margin it gives insertion to the antennæ (AT); and it is continued forward on the sides of the head by the genæ (G). The epicranium has no apodemes. It may have a few ridges on parts subject to strains, and it has a rim around the large eyes, and thickenings for the insertion of the antennæ; but there are no such ridges as to suggest segmentation in this region. This agrees with Balfour's conclusion (Comparative Embryology, chap. xvii) that the procephalic region does not correspond with the pos

terior parts, and that "the antennæ can hardly be considered to have the same morphological value as the succeeding appendages."

The clypeus or "face" affords insertion at its lateral borders to the mandibular condyles, whose cup belongs rather to it than (as usually stated) to the gene. It is strengthened by ridges so as to bear the strain of these appendages. The hind border of the clypeus bends down into a strong transverse ridge whose extremities at both sides give insertion to the tips of two stout endocranial pillars (mc in fig. 2). These pillars (which we shall term the mesocephalic pillars) descend obliquely downward through the eranial cavity, and have their lower insertion in the floor of the

skull, just in front of the occipital foramen. They are shown (мC) in figures 2 and 3, and also in the ant in figure 4.

These pillars arise by strong roots from the most rigid part of the cranial floor, and give support above to the clypeus which has to bear the mandibles. They also afford attachment to muscles and serve to limit the delicate organs of the head. Hence a bee's head is strong though its shell is rather thin. Near the top each pillar divides into two branches, so as to widen the surface of insertion. In the ant's neck I observed stout tendons so placed as to antagonize their downward thrust.2

1 Beetles usually have the mandibular cup in a process descending on each side from the clypeus: but in Cotalpa the clypeus is turned under and has the cups on its angles. 2 Burmeister speaks of "a broad ridge from the lower margin of the occipital aperture, which is prolonged towards the frons in two points." He seems to have broken off the pillars and to have observed only their inferior fragments. By the kindness of Dr. Hagen my attention has been called to Dr. O. J. B. Wolff's elaborate essay and

These large pillars ascend in front of the cerebral brain-lobes, in the fossæ between the cerebral mass and the ophthalmic lobes. They thus pass between the ophthalmic and the antennal nerves; and Dr. Wolff has shown that near their base they give insertion to muscles which supply the antennæ. The eyes, being very large in this group of insects, pass forward so as to outflank the insertion of the antennæ and these pillars.

Burmeister assigns no endocranium to Diptera, Hemiptera, and Lepidoptera. He states that in the first two of these orders "the head is a mere horny bladder without any internal processes" (Manual of Entomology, Shuckard's Transl., p. 232). This may be true as to Muscidæ ; but I have elsewhere tried to show that the basal segment of the proboscis of Muscidæ represents the endocranium, then become an evertible pedestal for the proper mouthparts.3 There is also in them a small arch thrown across the foramen magnum, corresponding to the jugum of the bee (as named by Wolff). In other Diptera, as the Gadfly and Mosquito, I find a pair of mesocephalic pillars, much as in the bee (in addition to a strong pharynx-case or splachnodeme, supporting the complex oral armature). As to Hemiptera, Burmeister's statement is only partially correct. The Squash bug (Coreus) has a pair of processes depending from the clypeus in the style of the upper part of the mesocephalic pillars, and Cicada has the pillars flattened out and attached to the sides of the head (the small eyes here not encroaching on their province), thus explaining the nature of the mesocephalic pillars as endodemes or involutions of the side wall of the cranium.

Lepidoptera likewise have a representative of these structures, in a strong sub-quadrate frame arising in front of the occipital foramen, and reaching forwards to near the roots of the proboscis. The Dragon fly has a ridge before the occipital foramen, sending up processes to the clypeal region, but these processes are broadened out and very thin, as in the weak and smaller clypeus.

The maxillæ and labium of insects are so closely connected in

drawings of the bee's head in Nova acta Leop. carol., xxxviii, 1. While in many points he has anticipated and advanced beyond what I have attempted, he has I think failed in some part to catch the meaning of what he describes. This seems due to a double defect, of failing to follow up the variations of parts in other groups of insects, and of supposing that he ought to reproduce the bones of the vertebrate skull in that of the insect. This last fault is fatal to the reception of his terminology, as where he terms the mesocephalic pillars “alisphenoids."

American Naturalist, March, 1879.