and Disaster, by Desor; and the fifth, on the Anatomy of Echinus, by Valentin. Among the Scutellæ Agassiz found well-marked differences between the living and fossil species, and that all the species of the genera Mellita, Rotula, and Encope, belong to the existing epoch. He found, moreover, that the species increase in size as they approach the present period. While he was publishing his work on the Echinoderms, this indefatigable naturalist also described and figured a large collection of fossil shells from the Oölite and Cretaceous formations, in a work entitled "Études critique sur les Mollusques de Jura et de la Craie," besides an annotated German translation of Buckland's "Geology," and French and German translations of Sowerby's "Mineral Conchology."
Notwithstanding the immense amount of work on his hands, Agassiz found time to prosecute his investigation upon the fresh-water fishes of Europe. The first part of this work, issued in 1839, is devoted to the genera Salmo and Thymallus. It appears as a folio of twenty-seven excellent plates, with descriptions illustrating six species of Salmo and one of Thymallus, one plate of each species being colored according to life, the others representing differences of age, sex, and locality. The second part, which did not appear till 1842, consists of a folio of plates and a volume of text on the "Embryology of the Salmons," by Carl Vogt, whom Agassiz had associated with him in his work. M. Vogt has given the most detailed descriptions and figures of the different organs, and the changes they undergo from the formation of the cellules, out of which the organs are developed, to the adult state. In regard to cell-formation, M. Vogt differs from Schwann in affirming that the germinative vesicle is formed prior to the nuclei and nucleoli. The volume closes with a history of the daily development of the embryo, from the exclusion of the egg to the birth of the young. This excellent work was never completed; Agassiz's departure for the United States shortly after, and his increasing responsibilities, prevented the perfection of his orignal plan.
In 1842 Agassiz began the publication of his "Nomenclator Zoologicus," an alphabetical list of every genus, with the name of the author, the work in which it originally appeared, the derivation of the name, and the family to which the genus belongs; the list embracing upward of seventeen thousand names. In the introduction the author examines the rules proposed by the British Association and those of the British Committee. He agrees with the rules proposing that the name given by a founder of a group, or the first describer of a species, should be retained, and that priority is to be conceded only to a name published in some universally accessible work. On the other hand, he objects to the restriction of priority to Linnæus and to the rule that would change a name previously in use in connection with some other genus in zoology or botany, as this would result in the sacrifice of half the names of recent times. He does not think it wise