The _Chalicodoma_, whose name of Mason Bee indicates the industry it exercises, is a hymenopterous relative to our Bees, long since carefully studied by Reaumur. It does not live in societies like the latter, and exhibits individual initiative and skill as great as the swallows. The females accomplish the work which I am about to describe. The little cells which they build are arranged, to the number of eight or ten together, in the most various places; sometimes on a pebble, sometimes on a branch, or, again, on a stone wall. (Fig. 36.) The insect collects earth as fine as possible, such as the dust of a trodden path, and tempers it with its own saliva. It places side by side these little balls of mortar and the work soon takes the form of a cupola, to the edge of which it constantly adds new deposits. The sun quickly dries the hole and gives it the necessary consistence. When the cell has acquired sufficient height, the _Chalicodoma_ abandons its occupation of mason, and visits flowers for pollen and nectar wherewith to fill the little chamber. It goes back to the nest, disgorges its supply, and returns to the field, until the little cup of earth is full to the edge. When the dwelling is thus prepared and provisioned, the insect lays an egg there and closes the upper part with a vault, built by successive deposits over the opening, which is more and more narrowed until it is finally shut up. Having completed a chamber, it passes on to the next, and so on until it has assured the fate of all its descendants. This hymenopterous insect certainly shows in its acts as an artisan an inevitable instinct: hereditary intelligence has become less personal and less spontaneous. In certain cases, however, the instinct loses its rigidity and automatism. Thus, when a _Chalicodoma_, at the moment of preparing to accomplish its task, finds an old nest, still capable of repair although dilapidated, it does not hesitate to take possession of it and to silence its assumed innate instinct of building. It profits by the work already done, and is content to fill up the cracks or to re-establish the masonry where defective; then it provisions the renewed cells with honey, and lays its eggs in them. In certain circumstances it shows itself still more sparing of trouble, and boldly rebels against the law which seems to be imposed on it by nature. If it feels itself sufficiently strong, the _Chalicodoma_ throws itself on one of its fellows, a peaceful constructor that has almost completed its work; it chases it away, and takes possession of its property to shelter its own eggs. Instead of manufacturing the cell from bottom to top, it has only to complete it. Such acts evidently show the reflection appearing through instinct. Besides the Swallows, of which I have already spoken, birds offer us several types of skilful construction with tempered earth.