Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/106

96 in the higher operations directed by intelligence, the being acquires in a gradual manner, and only after a lengthened experience, the perfect manner of working. In the one case instinct incites the being automatically, or through the excitory outward impressions, to perform the acts; in the other, an intelligent mind first appreciates the impres sions, and, through the educative training of experience, is enabled to perform the acts, and to understand in a greater or less degree the reasons which prompt and justify them. Apart from the possession of high instincts, however, we find ants, in common with many other insects, to be pos sessed of very perfect senses. In addition to the large compound eyes with which most insects are provided, they possess simple organs of vision. The sense of smell also appears to be represented in the ants and insects generally, but the seat of this sense has not been well or satisfactorily determined. Judging from analogy, however, the olfactory apparatus has been supposed to reside in the basal joints of the feelers or antennae. Ants have been long observed to follow accurately the track of their companions. Bonnet concluded that they were enabled to follow up this line of march by their scent, and in proof of this he repeatedly drew his finger at various parts across the line of march. The ants, on arriving at the interrupted spots, seemed to lose scent, and directed their steps in an irregular and hesitating manner, but having once crossed the interrupted space of the finger track, they resumed their journey once more in a regular manner along the line of march. Latreille, with the view of ascertaining if the sense of smell resided in the antennas, cut off these organs in several ants, when he found that they appeared to lose their way, and to be incapable of directing their further steps. It may, how ever, on obvious grounds be doubted whether this experi ment may be deemed at all satisfactory or conclusive on the point. In this experiment it was noticed that the neighbouring ants appeared to observe the distress of their mutilated companions, and they seemed to stanch the wounds of the sufferers by an application of the organs of the mouth to the wounded surface. The antennæ in insects are certainly the organs of touch, but in ants these organs appear to subserve some undeter mined function, in that through their agency communication may be made from one ant to the other. M. Huber was so strongly impressed with this latter fact, that he applied the term langage antennal to the intercourse which he sup posed took place between ants through the media of the antennae. For example, by each ant striking its head against its neighbour, and by the transmission of this impulse, the whole ant-community appeared to be warned of danger, and in other ways, but chiefly through the antennae, the sense of danger appears to be appreciated by each member of the colony. The food of ants has formed a debatable point ever since the attention of naturalists was directed to the investigation of their economy. As already remarked, many species are truly carnivorous, and prey upon the soft parts of other insects, and particularly of larva?, which they are enabled to seize and capture with little danger and trouble. The well- known partiality of ants for animal food is taken advantage of by those who wish to obtain the hard parts or skeletons of animal forms ; since by placing an animal body within reach of an ant-colony, the soft parts are gradually eaten away, and the harder portions are left intact. In tropical climates, rats, mice, and poultry, even in a living state, are said to succumb to the attack of these creatures; and man himself, as related by Prdvost in his Histoire General des Voyages, is even subject to the attacks of ants. Prdvost relates that an Italian missionary in Congo was awakened from sleep by his negroes, with the intelligence that an immense horde of ants was invading his house. Before he could rise they had already covered his legs, and the floor of his house was carpeted by a thick layer of the invading forms. Fire seemed to be the only preventive to their onward march ; and it was stated that cows were known to be devoured in their stalls by these creatures. These remarks may be viewed as applying more particularly to the white ants or termites, of which an account will be given, afterwards. For sugar ants seem to have a special pre dilection ; and they appear not only to obtain the saccharine matter from vegetables, but also to abstract it from animal sources. The aphides, or plant lice, become in this way the subjects of very extraordinary attentions on the part of ants. The plant lice possess a glandular structure, situated at the extremity of the abdomen, which communicates with the external surface by two small ducts. This gland- secretes a sweet or saccharine liquid of viscous nature, of which ants are extremely fond, and the aphides appear to be literally " milked " by their smaller neighbours. The antennae of the ants in this case also appear to be the media of intercourse between the aphides and themselves, and by touching the abdomen of the plant lice with the antenna?, a drop of the saccharine liquid exudes from the gland, which is eagerly seized upon by the ants ; and in this fashion the milking process is continued until the ant is satisfied. The aphides, in this instance, appear voluntarily to surrender themselves for the purpose of affording the saccharine matter; but it has been also alleged that certain species of ants keep aphides within their nests for the pur pose of affording the desired matter. Whether or not this alleged domestication of the aphides by ants is to be deemed worthy of belief yet remains to be proved. A single aphis may be occasionally seen surrounded by three or four ants, the latter ordinarily finding the aphides on the leaves of plants and in their natural habitat. The association of ants and aphides, strange as it may seem, is not, how ever, without its parallels in the history of the ant-colony. Thus wood-lice are not infrequently found as apparently normal guests within the ant-nest; and Siva of Pisa observed a species of grasshopper, to which he has given the name Gryllus myrmecophilus, which inhabits the nest of an Italian ant. The ant-nest, in fact, appears to be the normal: habitation of this grasshopper. The ant-nest forms a very interesting subject for consideration, and the various groups of ants differ widely in the outward form and internal plan according to which the nests are constructed, as well as in the materials of which the habitations are built. Clay, earth, and vegetable matters form the chief sources of supply, and excavations in the ground, or erections above ground, in trees, walls, and house-roofs, may be mentioned as the most common situations for the nests. The internal arrangement also varies even to a greater extent than the external appearance or materials. The general plan of the nest shows an arrangement of flats or stories, connected throughout by passages, and supported by definite pillars or partitions. The chief ends and objects in the construction of the nest appear to be directed to the preservation of the larva?, and to their protection from changes of temperature. During the night the larva? are placed in the furthest chambers of the nest, the entrance to the nest being carefully secured for warmth and for ensuring protection from the raids of enemies. In the morning the larva? are transferred by the diligent neuters to the outer chambers, to which the sun s heat has access ; or they may even be exposed directly to the sun. A change of temperature or weather is sufficient to set the watchful neuters on the alert, and to cause them to hurry the larvaa to the inner recesses of the abode, where they may be safely protected from the variable effects of the climate. Some of the most curious and extraordinary traits in ant-character relate to the acquiring by certain ants (e.g. Amazon-