seen thrusting her ovipositor into her prey without ovipositing and merely for the sake of obtaining food, or she may feed at a punc ture she has made while ovipositing. Obviously feeding and oviposition are here congenitally, or hereditarily conditioned reflexes, to use Pawlow's expression. In other words, the internal hunger and reproductive stimuli, or appetites, are so intimately associated with one another that mere contact with the prey releases either the feeding or the ovipositing reactions, or both. And, of course, both of these reactions are purely selfish, the one being concerned with getting food, the other with getting relief from the discomfort of egg-pressure in the ovaries, and both may initiate elaborate trains or patterns of behavior (instincts). This is true not only of the parasitoids but also of insects in general.

Turning now to the solitary wasps we find that, like the parasitoids, they prey on other insects and that each species of wasp usually has a predilection for a particular species (Figs. 18 and 19), genus or family of insects, or even for a particular sex, as in the case of one of our common wasps, Aphilanthops frigidus, which preys only on queen ants. The chief difference

between the parasitoid and the solitary wasp lies in the fact that the latter lays her egg on or near her victim after stinging it till it is motionless. The sting is merely the ovipositor which is now used only for defence or for reducing the prey to impotence, while the mouth-parts and especially the mandibles are used for obtaining food. Many solitary wasps, after stinging their prey,

A. Female of a Bethylid wasp Epyris extraneus, of the Philippines; B. Tenebrionid beetle, Gonocephalum seriatum; C. Larva of the same with egg of E. extraneus on middle of ventral surface; D. Young E. extrancus larva feeding on the larva of G. seriatum; E. Later stage of same; F. Pupa of E. extraneus; G. Cocoon of same. (After F. X. Williams).

devour it in part or entirely, or chew, i. e., malaxate, its neck and lap up the exuding juices. This behavior is essentially like that of the parasitoid, and in its more frequent, feebler manifestations may be regarded as a vestigial feeding. The adult wasp is no longer as carnivorous as its ancestors, because she has come to rely to some extent on the energizing nectar of flowers, but this substance contains no proteids and is therefore an improper food for her growing larval young. Roubaud and Rabaud have recently shown that the stinging of the prey follows reflexly as soon as it has been seized and comes in contact with the wasp's sternum, and that the accidental position of the prey when it thus releases the reflex determines the point where it will be stung. Moreover, the stinging is repeated till the victim ceases to struggle and becomes motionless. Hence the stinging does not occur in the schematic manner nor necessarily in the nerve ganglia, as described by Fabre. It has also been shown that the venom introduced into the tissues of the prey by the sting produces paralysis or even death and also acts as an antiseptic in preserving the prey from decomposition for weeks or even months while the larva that hatches from the wasp's egg is feeding on the tissue, but these properties of the venom are accidental and unforeseen. Hence Fabre's and Bergson's contention that the solitary wasp is a clairvoyant surgeon, with an intuitive knowledge of the internal anatomy of the particular insect on which it preys, may be dismissed as a myth.

FIG. 20

graph by Prof. Carl Hartman).

The explanations here given of the malaxation and stinging of the prey are purely physiological, but it is not at all certain that such explanations are applicable to the entire behavior cycle of the solitary wasp. Before enquiring into this matter, it will be advisable to sketch very briefly the behavior of a typical Sphex as a paradigm of the whole group of Sphecoids and solitary Vespoids. The female Sphex, after mating, digs in sandy soil a slanting or perpendicular tunnel and widens its end to form an elliptical chamber. She may thereupon close the entrance, rise into the air and fly in undulating spirals over the burrow, thus making what is called a "flight of orientation," or "locality study," because it enables her to fix in her sensorium the precise position of the burrow in relation to the surrounding objects, so that she may find. the spot again. Then she flies off in search of her prey, which is a particular species of hairless caterpillar (Fig. 20). When it is found, she stings it into insensibility, malaxates its neck, while imbibing the exuding juices, and drags it or flies with it to the entrance of her burrow. Here she drops her victim and, after entering and inspecting the burrow, returns and takes it down into the chamber, glues her egg to its surface and closes the burrow by filling it with sand or detritus collected from the surrounding soil (Figs. 21 and 22). As soon as the next egg matures in her ovaries she proceeds to repeat the same behavior cycle at some other spot. In the meantime the provisioned egg hatches, and the

Burrow of Sphex procerus in section, showing filling of débris in the tunnel and the paralyzed sphinx moth caterpillar in the cell, with the egg glued to its side. (Photograph by Prof. Carl Hartman).

larva, after devouring the helpless caterpillar, spins a cocoon, pupates in situ and eventually emerges as a perfect Sphex.

Some of our species of Sphex actually tamp down the filling of their burrows with a small,, carefully selected pebble, held in the mandibles and used as a hammer or pestle (Fig. 23).

This

(After G. W. and E. G. Peckham).