A Treatise on Zoology

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THE first instalment of the long-expected “Oxford Zoology”—first, that is to say, in order of publication—will be heartily welcomed as filling a distinct gap in zoological literature, and not of this country alone. During the latter half of the nineteenth century scientific literature has accumulated with such rapidity as to render it practically impossible for a zoologist at the present day to master thoroughly more than a limited part of his subject. To acquire a knowledge of the results gained in fields other than that which he has made his speciality, he must be dependent to a large extent upon the manuals and guide-books compiled by those who are sufficiently familiar with the latest discoveries in particular branches of zoology to be able to give a clear and critical account of the present state of knowledge in these departments. Nowhere is this necessity more strongly felt than in dealing with the Echinoderms, a group in which the student is confronted, on the one hand, with intricate morphological problems and with phylogenetic questions of a most puzzling kind; and, on the other hand, with such a vast array of extinct types that the nonexpert feels at once out of his depth when attempting to obtain an adequate knowledge of them. In the Pelmatozoa, practically half the phylum, we find a group of the greatest historical and phylogenetic importance, but one in which the existing forms teach us no more about the race in the past, and regarded as a whole, than do the modern Egyptians about the former dynasties whose remains are entombed in their land. The abundance of forms unearthed by the palæontologist has called forth a literature which exemplifies fully the danger of something like a deadlock in zoological science, as the result simply of its fertility. The student soon loses his way and finds himself struggling with a mass of hard facts and contradictory hypotheses, due on the one hand to the great diversity of form and structure in the objects themselves, and on the other hand to difficulties inseparable from the study of animals known almost entirely as fossils. Any one who has endeavoured, for instance, to gain an acquaintance with the structure and evolution of fossil Crinoids from the voluminous works of Messrs. Wachsmuth and Springer and other writers must have felt the urgent need for a guide and interpreter, failing whom it was necessary either to study deeply or to pass lightly by, to become an expert or to be content with ignorance. Yet no one with even a superficial acquaintance with the problems of Echinoderm morphology and phylogeny would willingly pass over the extinct forms, and least of all the more ancient Pelmatozoa, such as the Cystids and their allies, since it is obvious that here, if anywhere, is to be found in a concrete form the solution of many puzzles in the evolution of the phylum. Nowhere is palæontology, as a source of material evidence for theories of phylogeny, given so fair a trial as in the case of Echinoderms with their complete skeleton and consequent abundance of well-preserved fossil types, and it must be conceded that palæontology, if it condescends to speak clearly, can give the only final judgment in questions of evolution and ancestral history.