We find two classes of intelligent actions among the Hymenoptera which are sufficiently distinct to be considered separately, although, like all natural groups, they grade into each other. The first of these includes those actions that are performed by large numbers in a similar fashion under like conditions, while in the second class each act is an individual affair,—as where a single wasp, uninfluenced in any way by the example of those about it, displays unusual intelligence in grappling with the affairs of life. Examples of the first class are found in such modifications of instinct as are shown by Pelopæus and other wasps in the character of their habitations. Pelopæus, instead of building in hollow trees or under shelving rocks, as was the ancient custom of the race, now nests in chimneys, or under the eaves of buildings. We have found T. rubrocinctum taking advantage of the face of a straw–stack that had been cut off smoothly as the cattle were fed through the winter. The same power of adaptation is shown by Fabre’s experiment with Osmia, in which he took two dozen nests in shells from a quarry, where the bees had been nesting for centuries, and placed them in his study along with some empty shells and some hollow stems. When the bees came out, in the spring, nearly all of them selected the stalks to build in as being better suited to their use than the shells. All of these changes are intelligent adaptations to new modes of life, serving to keep the species in harmony with its surroundings. The same thing may be seen when a number of social wasps work together to replace the roof of their nest when it has been torn off. An instance of the second class is seen in one of our examples of Pompilus marginatus. This species, while searching for a nesting–place, leaves its spider lying on the ground or hides it under a lump of earth, in either of which positions the booty is subject to the attacks of ants; the wasp in question improved upon the custom of her tribe by carrying the spider up into a plant and hanging it there. We have now and then seen a queen of Polistes fusca occupy a comb of the previous year instead of building a new one for herself,—showing a better mental equipment than her sisters who were not strong–minded enough to change their ways, and so built new nests alongside of unoccupied old ones which were in good condition. In Bembex society it is good form to close the door on leaving home, but sometimes a wasp will save time by leaving the entrance open. This, however, is a doubtful case, as the advantage would, perhaps, be more than balanced by the exposure of the nest to parasites.