Mr. F. Smith, in his "Catalogue of British Bees," says of this genus: "No one appears to know anything beyond the mere fact of their entering the burrows of Andrenidae and Apidae, except that they are found in the cells of the working bees in their perfect condition: it is most probable that they deposit their eggs on the provision laid up by the working bee, that they close up the cell, and that the working bee, finding an egg deposited, commences a fresh cell for her own progeny." He has, however, found two specimens of Nomada, sexfasciata in the cells of the long-horned bee, Eucera longicornis. He also states, that while some species are constant in their attacks on certain Halicti and Andrenae, others attack different species of these genera indiscriminately. In like manner another Cuckoo bee (Coelioxys) is parasitic on Megachile and Saropoda; Stelis is a parasite on Osmia, the Mason bee: and Melecta infests the cells of Anthophora. The observations of Mr. Emerton enable us still further to clear up the history of this obscure visitor. He found both the larva and pupa, as well as the perfect bee, in the cells of both genera; so that either both kinds of bee, when hatched from eggs laid in the same cell, feed on the same pollen mass, which therefore barely suffices for the nourishment of both; or the hostess, discovering the strange egg laid, cuckoo-like, in her own nest, has the forethought to deposit another ball of pollen to secure the safety of her young. Is such an act the operation of a blind instinct? Does it not rather ally our little bee with those higher animals which undoubtedly possess a reasoning power? Its _instinct_ teaches it to build cells, and prepare its pollen mass, and lay an egg thereon. Its _reason_ enables it, in such an instance as this, when the life of the brood is threatened, to guard against any such danger by means to which it does not habitually resort. This instance is paralleled by the case of our common summer Yellow bird, which, on finding an egg of the Cow bunting in its nest, often builds a new nest above it, to the certain destruction of the unwelcome egg in the nest beneath.