Aside from insects, we know only a little about orientation with terrestrial articulates. That is why it will be interesting to report the following observation concerning Agelena labyrinthica, a very common spider which wanders about during the summer, while in the autumn it constructs funnel-shaped nests upon hillside herbs. On a beautiful day in the month of August, I noticed (1909) an Agelena carrying a grasshopper which was mutilated but still fresh. I teased the creature in order to make it leave its prey, and I chased it a little distance away,- some centimeters at first, then ten centimeters, then twice that distance. Each time it made a half-turn and came back to the grasshopper. I drove the spider forty centimeters away, and it returned again in its footsteps, and, crossing the short turf, where it stopped, several times moving its palpi, finished by directing itself straight and seizing the grasshopper once •more. The animal was, then, capable of orienting itself toward a known point which it could not see. I believe that the spider remembered the direction taken in its chase and followed back the same route, but I also think that it was helped by the sense of smell and that this sense has its seat in the palpi which it feverishly waved. .The nest spiders are known from their tactile sensitiveness, but their olfactory power is still mysterious and must soon be studied.
Orientation to a point is better known with the terrestrial insects. ' ' By scent and by sight, ' ' says Fabre, the sacred scarab very quickly finds its ball which an accident has caused to roll away from it. The predatory wasps, which return heavily laden, are not equally apt in returning to the nest. Sphex subfuscatus, which captures the large Italian grasshopper, is one of the species best endowed in this regard because it carries on a minute scouting. "When it leaves the burrow which it has dug, to go and search for its grasshopper," says Ferton, "the Sphex pivots on itself without leaving the ground, probably to examine the aspect of the place, . . . several times, and at different points in the journey the wasp repeats this evolution. ' '
There are even differences of aptitude with the predators which store their victim. Pompilus fuscipennis appears the most maladroit. While it is digging its burrow, the insect returns often to examine the inert prey, and although this is always in fact at a distance of only twenty or thirty centimeters, she does not find it easily. At times she draws it nearer the nest, in which case she can find it quickly. The Peckhams have given a diagram of the marches and countermarches executed by an individual of this species. What cleverness, on the contrary, is shown by a pompi-lid studied by Fabre! This one interrupts her mining work to visit the spider, but she goes in a straight line, and when the victim is removed a short distance she finds it very quickly, for she remembers the place where she left it. Fabre says:
The insect comes always to the last spot, without bothering about the others. I marvel at the memory of this myrmidon. It was enough for her to have seen once, in haste, a spot which did not differ in any respect from a number of others, to recall it very well in spite of her preoccupation as a miner excited by her underground work.
It is, indeed, sight which guided her, not odor, for she passed over the spider without noticing it when it was covered with a delicate leaf. She had a surprising memory for places.