Viehmeyer on the one hand and Turner on the other have arrived at the same result by different methods. Viehmeyer (1900) reared Leptothorax unifasciatus which had established their nest in earth in the middle of a transparent bottle. Having carried the bottle near to a window, he saw the insects dig another nest on the opposite side and carry their larvae to it. While they were moving, going from the light to the dark side, he turned the bottle 180 degrees, which had the result of placing the new nest toward the window, but did not prevent the ants from continuing their moving toward the opposite side. The experiment of Turner (1907) more nearly recalls that of Lubbock. Upon a horizontal platform communicating by several bridges with an artificial nest, the ants were thrown with their eggs. When their fright passed, the creatures thought of their precious progeny, which they carried to the nest, using one of the bridges. The route once established, the lamp, which lighted this scene from the side, was carried to an opposite point, which caused new trouble. Soon, however, the -ants again began their regular march, but, oriented by the lamp, they went the reverse way and reached the nest by the opposite bridge.
Contrary to Santschi, Cornetz thinks that the ant directs itself "independently of the position of the sun," that it preserves in its sensorium a "pure direction" without any modification, and he advances as a proof the fact that it directs itself in the shade as well as in the sunlight. To this we may reply, with Santschi, that even on a shady journey the side toward the sun is lighter, the ants are more sensitive than we are to differences of radiation, since they react to the ultraviolet, and that, even in the night, it is very possible that they orient themselves by the stars in a spot covered by zones of shade and light. These hypotheses have in them nothing of the improbable, although it will be necessary to justify them by experiment. On the other hand, it is not to be doubted that ants can orient themselves, not only by the sun, but by all the large objects which surround them. We do not ignore the observation of Forel upon the Lasius, which followed him in his movements and confused him with a tree. Santschi reports several similar facts,-a worker of Messor correcting its orientation by the presence of a great heap of sheaves when disturbed in the experiment of the mirror, Camponotus orienting itself by a date-tree, Aphcenogaster taking a wall for a point of guidance. Thus to the guidance from the sun, which is certainly of prime importance, may be added, and is added in many cases, the guidance from different more or less lighted zones, and it is by means of these multiple things that the insect orients itself. "If one of these zones rapidly disappears from the visual field (passage of the sun into shadow)," observes Santschi, "the insect continues to use the remaining zones, but if there is a sudden transposition from these zones (experiment of the mirror) the insect, taking a new direction corresponding to the change, only maintains its orientation in relation to the guides of an habitual preponderance. '9
How can we explain the orientation of the insect when some catastrophe has destroyed all of the guiding points in the vicinity of the nest, on the theory of resting zones?
In the experiment of Cornetz upon Cataglyphis, and in that of Wasmann on the sanguinary ants, certain individuals returned to the old nest, but they did not know whether or not the individuals had retained the habit of visiting this nest, and it would not have been surprising if all had returned. We may, in fact, believe that, upon the destruction of their nest, the workers fled in all directions, and that certain ones, finding themselves on an unknown route, recognized the guiding points which led them to the old nest. In fact, it is useless to discuss experiments of which the details are not all known, since these details may have a fundamental importance. If it were established that our insects can orient themselves solely by the light of the sun, we should be "led far," observes Cornetz,-that is to say to the conception that ants know how to estimate its height at different times of the day. Evidently this supposition cannot be admitted without a rigorous experimental examination. Although it appears strange and improbable, it does not perhaps exceed the faculty of apprenticeship of these animals, to whom orientation is a vital necessity. In admitting "that the ant can preserve a direction independent of environment,7 7 Cornetz departs still more from the truth. We cannot too highly esteem the patient researches of this experimenter and the progress he has made in the difficult problem which we are considering, but we think we ought to say, with Santschi, "as far as the new and inexplicable facts concerning guiding points are not registered and verified,, so far shall we not have demonstrated the seat and the nature of the sense of pure direction." To admit a sense of this kind "will remain a useless hypothesis and an explanation which should be reserved as a last resource."
To sum up, ants orient themselves essentially like flying insects,-that is to say, by the visualized aid of near or distant bodies, utilizing their memory of places and the recollection of impressions which they have received through other senses, especially that of smell. There are many degrees between the eyes of a wasp or of a bee and those of the most poorly endowed ants, and it would be at least surprising if a mysterious sense of orientation had come to the latter and not to the former. Incapable of leaving the ground, and provided with eyes having commonly less numerous facets, the workers of the ants have a narrower horizon,-and that is all.
According to the condition of their eyes, and the conditions under which they live, ants employ in their orientation the eyes or the 'antennae. Forel has stated that Formica pratensis, after their eyes had been varnished, "had trouble in finding their way while outside; while they "directed themselves easily in their rearing-boxes " filled with odors. If the insect is completely blind like Eciton carolinse, then it guides itself exclusively by smell and by touch. Forel says (1900) :
Throw a handful of Eciton with their larvae upon an absolutely strange ground. ... In such circumstances- in which other ants spread out in disorder and take an hour or more (sometimes less) to reach order again, to bring their nymphs together, and especially to remember the surroundings-the E citons organize themselves without losing a minute. In five minutes they have formed distinct files of workers which do not leave one another, tapping the earth with their antennae, exploring all the holes and cracks until they find a convenient cavity. Then their arrangements are executed with an astonishing order and rapidity. The workers follow and understand one another, as if at a password, and in a very short time everything is all right.