These form a new genus, but are most nearly allied to Cythere, a marine type.

It is believed that the transmission of this species from one tree to another must be effected by the young crustacea, which are very minute, clinging to beetles, many of which, both terrestrial and aquatic, also inhabit the bromelia leaves; and as some water-beetles are known to frequent the sea, it is perhaps by these means that the first emigrants established themselves in this strange new abode.

Bromeliae are often very abundant on trees growing on the water's edge, and this would facilitate the transition from a marine to an arboreal habitat.

Fritz Mueller has also found, among the bromelia leaves, a small frog bearing its eggs on its back, and having some other peculiarities of structure.

Several beautiful little aquatic plants of the genus Utricularia or bladder-wort also inhabit bromelia leaves; and these send runners out to neighbouring plants and thus spread themselves with great rapidity.
_The Importance of Isolation._ Isolation is no doubt an important aid to natural selection, as shown by the fact that islands so often present a number of peculiar species; and the same thing is seen on the two sides of a great mountain range or on opposite coasts of a continent.