Cuvier, the great leader in zoölogy, to whom the book was dedicated, wrote back: "You and M. de Martius have done me honor in placing my name at the head of a work so admirable as the one you have just published. The importance and the rarity of the species therein described, as well as the beauty of the figures, will make the work an important one in ichthyology, and nothing could heighten its value more than the accuracy of your descriptions. It will be of the greatest use to me in my 'History of Fishes.'... I shall do all in my power to accelerate the sale among amateurs, either by showing it to such as meet at my house, or by calling attention to it in scientific journals."
Another project had now taken form in Agassiz's active brain, his great work on "Poissons Fossiles," which a few years later placed him in the front rank of scientific men. He wrote to Auguste: "Having, by permission of the director of the museum, one of the finest collections of fossils in Germany at my disposition, and being also allowed to take the specimens home as I need them, I have undertaken to publish the ichthyological part of the collection. Since it only makes the difference of one or two people more to direct, I have these specimens also drawn at the same time. Nowhere so well as here, where the Academy of Fine Arts brings together so many draughtsmen, could I have the same facility for completing a similar work; and as it is an entirely new branch, in which no one has as yet done anything of importance, I feel sure of success; the more so because Cuvier, who alone could do it (for the single reason that every one else has till now neglected the fishes), is not engaged upon it. Add to this that just now there is a real need of this work for the determination of the different geological formations." And then he urges Auguste to intercede with his uncle at Neuchâtel for one hundred louis. "At this very time, when he was keeping two or three artists on his slender means," says his wife, "he made his own breakfast in his room, and dined for a few cents a day at the cheapest eating-houses. But where science was concerned the only economy he recognized, either in youth or old age, was that of an expenditure as bold as it was carefully considered."