Lieut. de Crispigny has observed a sea anemone (_Actinia crassicornis_) living on good terms with a malacopterygian fish, the _Premnas biaculeatus_. This fish penetrates into the interior of the anemone; the tentacles close round it, and it lives thus for a considerable time enclosed as in a living tomb. Mons. de Crispigny has kept these animals alive for more than a year, in order to make careful observations on them. A fish known by the name of _Oxybeles lumbricoides_ has been also found in the Indian Seas, which modestly takes up his quarters in a star-fish (_Asterias discoida_). Another case of _commensalism_ has been made known to us by Professor Reinhardt of Copenhagen. A siluroid of Brazil, of the genus _Platystoma_, a skilful fisherman, thanks to his numerous barbules, lodges in the cavity of his mouth some very small fishes, which were for a long time considered as young siluroids; it was supposed that the mother brought her progeny to maturity in the cavity of the mouth, as marsupials do in the abdominal pouch, or as some other fishes do. These messmates are perfectly developed and adult, but instead of living on the produce of their own labour, they prefer to instal themselves in the mouth of an obliging neighbour, and to take their 8 tithes of the succulent morsels which he swallows. This little fish has received the name of _Stegophilus insidiatus_. We see that in the animal world it is not always the great which take advantage of the little. Still, let us not be deceived; there are fishes in the latitude of the Island of Ceylon which really hatch their eggs in the cavity of the mouth, and we have seen some in the museum at Edinburgh, labelled with the name of _Arius bookei_. Louis Agassiz has made the same observation on a fish of the Amazon, which has also been recognised by Jeffreys Wyman. One fish wraps up its eggs in the fringes of its branchiæ, and protects them till they are hatched; another lays its eggs in holes hollowed out by itself in the steep banks of the river, and protects the young ones after they are hatched. To hatch the eggs in the mouth is not more extraordinary than to hatch them in any other part of the body. The _Sygnathidæ_ hatch theirs in a pouch behind the anus; and it is a curious circumstance that the females do not undertake this duty. The males alone carry their progeny with them. This recalls to our recollection that curious example of the birds known under the name of _Phalaropes_, among which the males only hatch the eggs. The female of the cuckoo abandons her eggs, and entrusts them to the female of another bird.