Speaking generally, birds are accomplished architects. Certain of them are, however, content with a rudimentary cavern. There is no question here of those who retire to clefts in the rock or in trunks of trees, for in these cases the cavity is only the support of the true house, and it is in the construction of this that the artist reveals his talent. I wish to speak of animals which remain in a burrow without making a nest there. A Parroquet of New Zealand called the _Kakapo_ (_Strigops habroptilus_) thus dwells in natural or hollowed excavations. It is only found in a restricted portion of the island and leads a miserable life there, habitually staying in the earth and pursued by numerous enemies, especially half-wild dogs. It tries to hold its own, but its wings and beak do not suffice to protect it, and the race would have completely disappeared if these birds were not able to resist, owing to the prudence with which they stay within their dwellings. They profit by a natural retreat, or one constructed in rocks or beneath roots of trees; they only come out when impelled by hunger, and return as soon as they can in case of danger. A large number of animals also hollow out shelters for their eggs, with the double object of maintaining them at a constant temperature and of concealing them. Most reptiles act in this manner. The way in which a Tortoise, the _Cistudo lunaria_, prepares its nest is extremely curious. When the time for this labour arrives, the tortoise chooses a site. It commences by boring in the earth with the end of its tail, the muscles of which are held firmly contracted; it turns the tail like a gimlet and succeeds in making a conical hole. Gradually the depth of the hole becomes equal to the length of the tail, and the tool then becomes useless. The _Cistudo_ enlarges the cavity with the help of its posterior legs. Using them alternately it withdraws the earth and kicks it away, then piles up this rubbish on the edge of the hole, arranging it so as to form a circular rampart. Soon the posterior members can take nothing more from the too distant bottom. The moment for laying has now come. As soon as the egg arrives at the cloaca one of the feet seizes it and lowers it gently into the nest, while the second foot seizes another egg, which during this time had appeared at the orifice. This manipulation lasts until the end of the operation, when the tortoise buries all its family, and to flatten the prominence which results she strikes it repeatedly with her plastron, raising herself on her legs.