work on fishes, “Histoire naturelles des Poissons,” of which the first volume appeared in 1828. The earlier volumes, in which Cuvier himself took his share, bear evidence of the freshness and love with which both authors devoted themselves to their task. After Cuvier’s death in 1832 the work was left entirely in the hands of Valenciennes, whose energy and interest gradually slackened, to rise to the old standard in some parts only, as, for instance, in the treatise on the Herring. He left the work unfinished with the twenty-second volume (1848), which treats of the Salmonoids. Yet, incomplete as it is, it is indispensable to the student. There exist several editions of the work, which, however, have the same text. One, printed in 8vo, with coloured or plain figures, is the one in common use among ichthyologists. A more luxurious edition in 4to has a different pagination, and therefore is most inconvenient to use. As mentioned above, the various parts of the work are very unequally worked out. Many of the species are described in so masterly a manner that a greater excellency of method can hardly be conceived. The history of the literature of these species is entered into with minuteness and critical discernment; but in the later volumes, numerous species are introduced into the system without any description, or with a few words only, comparing a species with one or more of its congeners. Cuvier himself, at a late period of his life, seems to have grown indifferent as to the exact definition of his species: a failing commonly observed among Zoologists when attention to descriptive details becomes to them a tedious task. What is more surprising is, that a man of his anatomical and physiological knowledge should have overlooked the fact that secondary sexual characters are developed in fishes as in any other class of animals, and that fishes undergo great changes during growth; and, consequently, that he described almost all such sexual forms and different stages of growth under distinct specific and even generic names. The system finally adopted by Cuvier is the following:-- _A._ POISSONS OSSEUX. I.--A BRANCHIES EN PEIGNES OU EN LAMES. 1. A MÂCHOIRE SUPÉRIEURE LIBRE. a. _Acanthoptérygiens._ Percoïdes. Polynèmes. Mulles. Joues cuirassées. Scienoïdes. Sparoïdes. Chétodonoïdes. Scomberoïdes. Muges. Branchies labyrinthiques. Lophioïdes. Gobioïdes. Labroïdes. b. _Malacoptérygiens._ _Abdominaux._ Cyprinoïdes. Siluroïdes. Salmonoïdes. Clupeoïdes. Lucioïdes. _Subbrachiens._ Sparoïdes. Pleuronectes. Discoboles. _Apodes._ Murenoïdes. 2. A MÂCHOIRE SUPÉRIEURE FIXÉE. Sclérodermes. Gymnodontes. II. A BRANCHIES EN FORME DE HOUPPES. Lophobranches.