double, but springs before the dogs and is off immediately. The chase presents none of the evolutions which we described above; it is nothing but a race between the herbivorous animal, who has on his side speed, and the carnivorous animal, who has endurance. From the condition of the animal and the speed of the hunting party one can determine beforehand the duration of the chase. We will not dwell longer on these facts so well known to hunters. It is, in fact, sufficient to go through a wood in Sologne, or in any other country abounding in game, to be convinced that the ground is traversed in every direction by trails which do not escape the experienced eyes of the poacher.
Birds also follow through the air roads invisible to our eyes, but which can be revealed by observation. The bird, like the quadruped, contracts the habit of always returning to the same point by the same route. We have watched for some time a group of pigeons that returned every day to the fields at the same time. In going, as in coming, they undeviatingly followed a line which we had marked out on the neighboring ground. We have observed the same regularity of route in the coming and going of two birds of prey.
The peasants know very exactly the points which mark the course of the migrations of birds, and turn this knowledge to account by hunting during certain seasons.
Similar observations have been made on fishes in the sea as well as in rivers, and the very exact information obtained is put to a daily use by fishermen.
We will not put further stress on an array of facts long since observed and known. We will limit ourselves to deducing from them a primary conclusion. In the air, on land, or in the water all animals follow routes definitely determined; their movements seem, therefore, to be subject to other laws than those of caprice or chance.
II.
The actions of animals are all dictated by a single law, which each one of them obeys in a different way. The animal is controlled by his environment. If he finds around his home an abundauce of the necessities of life, he moves about but little and his existence is passed in a very restricted domain. In the opposite case he lives a very active life, traversing his domain unceasingly, extending its limits as far as possible and sometimes going beyond them. Each animal is thus led to contract habits which become peculiar to him and which constitute his individuality. He obeys the call of instinct, but he seems to have the choice of the means of execution, a certain liberty, while he is simply under the influence of his surroundings. It is necessary to bear this in mind before fixing those general laws to which the movements of the individuals of each species are subject.
It is a fact known by experiment for some time that an animal moving about in a territory familiar to him is guided in finding his way back
