Agassiz’s beautifully illustrated “Contributions to the Natural History of the United States” cover many subjects in morphology and embryology, which are treated with such thoroughness and breadth of view as to give them a place among the zoological classics. The Essay on Classification, the North American Testudinata, the Embryology of the turtle, and the Acalephs are the special topics. These are summarized and discussed at length in the Journal (25, 126, 202, 321, 342, 1858; 30, 142, 1860; 31, 295, 1861).
The volume on the “Journey in Brazil” (1868) in joint authorship with Mrs. Agassiz is a fascinating narrative of exploration.
The conceptions which Agassiz held as to the most essential aim of zoological study are well illustrated in his autobiographical sketch, where he writes:[[174]]
“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!”
It is not surprising, then, that under such influence the older systematic studies should be replaced in large measure by those of a morphological and embryological nature.
The personal influence of Agassiz is still felt in the lives of even the younger zoologists of the present day. For the investigators of the present generation are for the most part indebted to one or another of Agassiz’s pupils for their guidance in zoological studies. These pupils include his son Alexander Agassiz, Allen, Brooks, Clarke, Fewkes, Goode, Hyatt, Jordan, Lyman, Morse, Packard, Scudder, Verrill, Wilder, and others—leaders in zoological work during the last third of the nineteenth century. Through such men as these the inspiration of Agassiz has been handed on in turn to their pupils and from them to the younger generation of zoologists.
The essential difference between the work of Agassiz and that of the American zoologists who preceded him was in his power of broad generalizations. To him the organism meant a living witness of some great natural law, in the interpretation of which zoology was engaged. The organism in its structure, in its development, in its habits furnished links in the chain of evidence which, when completed, would reveal the meaning of nature. Of all Agassiz’s pupils, probably William K. Brooks most fittingly perpetuated his master’s ideals.
Period of Morphology and Embryology, 1847–1870.
The new aspect of zoology which came as a result of the influence of Agassiz characterized the zoological work of the fifties and sixties, that is, until the significance of the natural selection theory of Darwin and Wallace became generally appreciated.
The work in these years and well into the seventies was largely influenced by the morphological, embryological and systematic studies of Louis Agassiz and his school. The structure, development, and homologies of animals as indicating their relationship and position in the scheme of classification was prominent in the work of this period. The adaptations of animals to their environment and the application of the biogenetic law to the various groups of animals were also favorite subjects of study.