Certain sensations may be so acute that for the moment they destroy all others. This phenomenon is not rare in man,- as witness "absorbed persons." It is commoner still with the arthropods and plays a very great part in the life of these animals, as numerous biologists have noted. One cannot easily distract a digger-wasp when she is paralyzing her victim, a dung-beetle when it is rolling its ball, a fly when it is drinking milk. Entirely absorbed in her work, the foraging bee, says Perez,1 seems oblivious of everything that is not the immediate object of her activity; whether she is returning or starting out, she seems to see nothing that goes on about her. Pillagers try to force the door (of the hive) ; she brushes past them without recognizing them; honey is spread on the table, she takes no care at all not to fall into it and become entangled in it. We know that ants recognize one another with their antennae, that they get along beautifully with the individuals of their formicary, while they engage in pitiless battle with those of another nest or with another species. In the last case everything else is forgotten in the ardor of the belligerents. ' ' One can,9 9 says Forel, "cut off several of their legs, or even cut them in two in the middle of the body and they will continue to fight and kill one another as if nothing had happened to them.9 9
1 J. Perez, Notes zoologiques, 1894. (Actes Soc. Linn. Bordeaux, v. 47. pp. 231-331).
As to the invasion of automatism into habits, it is subject to an essential rule which may be called "the rule of predominance," for this term expresses the fact that a single sensation or a small number of predominant sensations suffice automatically to release an act which opposes a more numerous group of sensations. An example taken from the observations of Ferton will help us to render very tangible the exact meaning of this rule. Ammophila holosericea is a predatory wasp like sphex and Pompilus, but, instead of paralyzing Orthoptera and spiders for its young, it attacks measuring-worms. It is necessary to collect four or five of these caterpillars before closing its nest, which it has dug in the sand. One of these wasps had just closed its filled nest and Ferton offered it a caterpillar already paralyzed by one of its congeners. The insect found this one excellent, carried it near its burrow, and began to remove the material which closed the latter. But finding the burrow already full, the wasp forgot the caterpillar and hastened to close the burrow and flew away. Then she saw the caterpillar again and resumed manúuvers. It is not doubtful, that, under normal conditions, the insect associates at least three different sensations before storing her prey: consciousness of the paralyzed caterpillar, of* the proximity of the nest, and of the incompletely provisioned nest. But, in the experiment, a single sensation seems to control the actions of the insect; the sight of the paralyzed insect automatically provoked the storing manúuver, and the sight of the open burrow the manúuver of closing.
It is especially from old sensations more or less strongly impressed, that the memory of articulates is made, and it is the recall of old sensations by new ones to which is due, in large part, the activity of these animals. But one can know the sensations of animals only by the external manifestations of which they are the cause, and, as Bohn justly observes: "All sensations do not manifest themselves externally" immediately; many remain latent in the memory and are recalled to manifestation by the occurrence of new associative sensations. A wasp has taken some honey treated with alum; she immediately draws away and begins carefully to clean her mouth parts. That is the external manifestation of a disagreeable gustatory sensation. But what sensations has a bee when it makes many visits to nectar placed upon a plate of uniform coloration? To know this it is necessary to move the plate a little and, in its place, to put a second, also provided with nectar but differently colored. Lubbock1 has tried this experiment, employing very different colors and, despite the substitution he has always found that the insect returns to the first plate, to which it has formed the habit of going for honey. Lubbock's bee associated the sensation of color with the sensation of taste: both were fixed in its memory, but while the second showed itself by journeys and meals, the second remained hidden, and, in order to make it evident, it was necessary to try the indirect method of moving the plate.
1 J, Lubbock, Ants, Bees and Wasps, 1882.