"At first, when a mere boy, twelve years of age, I did what most beginners do. I picked up whatever I could lay my hands on, and tried, by such books and authorities as I had at my command, to find the names of these objects. My highest ambition, at that time, was to be able to designate the plants and animals of my native country correctly by a Latin name, and to extend gradually a similar knowledge in its application to the productions of other countries. This seemed to me, in those days, the legitimate aim and proper work of a naturalist. I still possess manuscript volumes in which I entered the names of all the animals and plants with which I became acquainted, and I well remember that I then ardently hoped to acquire the same superficial familiarity with the whole creation. I did not then know how much more important it is to the naturalist to understand the structure of a few animals, than to command the whole field of scientific nomenclature. Since I have become a teacher, and have watched the progress of students, I have seen that they all begin in the same way; but how many have grown old in the pursuit, without ever rising to any higher conception of the study of nature, spending their life in the determination of species, and in extending scientific terminology! Long before I went to the university, and before I began to study natural history under the guidance of men who were masters in the science during the early part of this century, I perceived that while nomenclature and classification, as then understood, formed an important part of the study, being, in fact, its technical language, the study of living beings in their natural element was of infinitely greater value. At that age, namely, about fifteen, I spent most of the time I could spare from classical and mathematical studies in hunting the neighboring woods and meadows for birds, insects, and land and fresh-water shells. My room became a little menagerie, while the stone basin under the fountain in our yard was my reservoir for all the fishes I could catch. Indeed, collecting, fishing, and raising caterpillars, from which I reared fresh, beautiful butterflies, were then my chief pastimes. What I know of the habits of the fresh-water fishes of Central Europe I mostly learned at that time; and I may add, that when afterward I obtained access to a large library and could consult the works of Bloch and Lacepede, the only extensive works on fishes then in existence, I wondered that they contained so little about their habits, natural attitudes, and mode of action with which I was so familiar.