between the earth and the other members of the solar system were in past times the same as we now find them. The variation in the astronomical elements of the globe is so small that they are regarded as stable for the period covered by history, but this variation assumes great importance when the periods represented by geology are brought into consideration.

Lord Kelvin says the nebular theory of the evolution of the solar system, "founded on the natural history of the stellar universe, as observed by the elder Herschel and completed in details by the profound dynamical judgment and imaginative genius of Laplace, seems converted by thermodynamics into a necessary truth if we make no other uncertain assumption than that the materials at present constituting the dead matter of the solar system have existed under the laws of dead matter for a hundred million years." A large sun during the early stages of the earth's history is therefore a necessary result of what is believed to have been the genesis of our system. The earth is an extremely small fragment thrown off from the central sun at one of its periods of condensation, and by reason of its small dimensions its stellar phase would be comparatively short. On the other hand, the enormous mass of the sun would cool much more slowly, and its gradual contraction would provide an amount of energy sufficient to make good all that lost in radiation.

We may well suppose that when the sun had a diameter little less than the diameter of the orbit of Mercury the precipitation of water, geological and life phenomena, commenced on our earth. Such a nebulous sun would radiate for each unit of its surface less heat and light than the sun at present, but the total amount of radiant energy received by the earth might be greater than that received at present, and would be very differently distributed over the earth's surface. The Torrid Zone would be extended on either side of the equator to the forty-seventh parallel of latitude. The seasonal effects produced by the inclination of the earth's axis to the ecliptic would be annulled. There would be suppression of a twenty-four-hour night about the poles at any time of the year. A cone of effective solar rays would graze the earth along a small circle of the sphere; at the solstice the rays of light would touch one pole and envelop the other to the fortythird parallel of latitude, so that at this position of the earth four degrees of latitude-those between 43° and 47°-would have at the the same time a twenty-four-hour day and some portion of the sun overhead at noon. A sun the angular diameter of which is equal to twice the obliquity of the ecliptic, i. e., 47°, would thus produce at the poles during the whole year an insolation 18 per cent greater than at

1 Kelvin. Popular Lectures and Addresses, Vol. I, pages 421-422. London, 1891. 2 "Les géologues pourront trouver, dans le diamètre considérable de la masse solaire à ces époques, l'explication de l'égalité de climat dont paraît avoir joui la terre jusqu'au commencement de l'époque actuelle." (Wolf. Les Hypothèses cosmogoniques, page 32: Paris, 1886).

present, tending to a complete uniformity of climate over the earth's surface. When we take into consideration the effect of the earth's atmosphere, a sun with a diameter even half that here indicated would account for the paleothermic phenomena made known by the records of the past life on the globe. When seeking a rational explanation of the gradual evolution of the surface features of the globe, it is necessary to take into account the contemporaneous evolution of the other members of the solar system, and especially that of the central luminary. Bull. Soc. Géol. de France, Tom. 25, p. 777, 1868.

Blandet.

THE BIOLOGIC RELATIONS BETWEEN PLANTS AND ANTS.1

By Dr. HEIM,

Associate of the Faculty of Medicine at Paris.

In the study of natural sciences it is often an excellent plan to begin by stating a well-worn truism. To say, in the present state of our knowledge, that close relations exist between plants and insects is to utter such a truism.

At the close of the last century the wonderful discoveries of Koelreuter followed by those of Sprengel had already demonstrated such relations. It was upon the teachings of that genial thinker that was built a great part of the theory of selection given definitive form by the labors of Darwin. At that period, however, the relations between plants and insects, even when viewed by the light of evolution, were considered almost solely with regard to the cross-fertilization of vegetable organisms. The biologic relations between plants and ants have been fully examined only by our contemporaries. Though the topic is one of extraordinary fecundity, it is but little known to the general public.

Among the subjects that biology offers for our consideration some are especially fortunate in that their exposition requires no personal talent, their interest depending upon a mere recital of facts. One of these privileged subjects is the relations of plants and ants, and this selfish consideration has led me to choose it for my remarks.

As a preliminary to the study of the relations of ants to living vege table forms it will be well to rapidly examine the organs that insects use in establishing such relations. We need not dwell upon their legs, which are very movable and constructed upon the general plan of the legs of insects. The claws that terminate them are used by ants in clinging to rough surfaces, in scratching the ground, in rejecting refuse, in holding food. Between the claws are found very delicate organs, the pulvilli, by whose aid the insect can cling to smooth surfaces, whether vertical or horizontal, against the force of gravity, by means of an oily secretion that causes the foot to adhere by capillary

'Translated from the Compte Rendu de la 24me Sess. de l'Association Française pour l'Avancement des Sciences, 1895, prémière partie, pp. 31-75.

attraction. Upon the head of an ant are borne sense organs-compound and simple eyes, organs apparently olfactory in character, antennæ, and buccal organs. On either side of the buccal opening are two large chitinous pieces, triangular in shape, articulated so that they can be moved apart or toward each other in a horizontal direction like the two jaws of a pinchers, the surfaces in contact being usually cut like a saw. These mandibles have a most important office, serving both as a weapon and as a tool. They are, in fact, used as scissors for cutting, as pinchers for dragging or tearing, as a trowel is in tempering and laying on mortar, as a shovel for removing excavated matter. It might almost be said that the only use for which they are absolutely unfitted is that of mastication of food. Below and behind them are found the maxillæ, formed by three coarticulated pieces, movable, membranous in character, bearing on their surfaces several rows of hairs and gustatory papillæ. Like the mandibles, they can not serve in mastication, but they assist the lips and the palpi in the recognition and seizure of food. The maxilla bear the maxillary palpi, composed of from one to six pieces, organs especially tactile. The labrum, usually concealed under the epistoma, forms the anterior wall of the buccal opening. It is a flattened piece of variable form, often bilobate, capable of movement from behind forward in a horizontal plane. The lower lip forms the floor of the mouth and carries the ligula, an extensible piece which, because of its mobility, may be used for lapping or licking up fluids. The rows of gustatory papilla that it carries in front and behind are the principal seat of the sense of taste. On each side of the lower lip are inserted the labial palpi, usually smaller than the maxillary palpi, formed of from one to four pieces. These also are tactile organs. According to Forel the mandibles are never used for eating. The most attentive observations confirm this, and the disproportion between the mandibles and the maxillæ makes it evident. The mandibles remain closed and immovable while the ant is eating. The mouth is usually closed by the labrum, which is turned over it, downward and backward, covering entirely the anterior part of the maxillæ and of the lower lip. When the ant wishes to eat it makes a complex movement of the pharynx which pushes forward the ligula, together with the neighboring parts, raising the labrum like a lid. The maxillæ are too short and too weak to crush a solid; they can only draw into the mouth a liquid or semisolid. It is the ligula or tongue which is most used by ants when they eat, and, according to the apt expression of Lespés, they use it as a dog does when he laps. When the ants are dealing with a solid body inclosing a liquid they first tear it with their mandibles and then lap up its contents. The buccal apparatus can, then, be used for scraping, cutting, and licking.

Mention should be made of the apparatus for the production of venom. This is situated on the posterior part of the abdomen and, as we shall hereafter see, may render to plants, the friends of our insects, certain