Embryological Facts Research Articles

(1) Zoology: An Elementary Text-Book (2) Elementary Text-book of Economic Zoology and Entomology

(1) A NEW edition of “Shipley and MacBride” will receive a welcome from students and teachers of zoology, for the original work published in 1901-took at once a distinct place among text-books on account of the freshness and individuality of the authors' method. The present volume exceeds in length its forerunner by 100 pages, and many improvements have been introduced. For example, the groups of the flatworms, nemertines, rotifers, and nematodes have been brought from their former position at the end of the volume following after the mammalia, and placed before the annelida. The arrangement, which startled readers of the first and second editions, was intended to emphasise the authors' opinion that these groups are not coelomata, and this opinion is still set forth, perhaps too dogmatically, in the clear “Introduction to the Coelomata” that precedes immediately the account of the annelids. The authors have accepted Goodrich's distinction-now familiar to zoologists-between true nephridia and ccelomo-ducts(such as the excretory tubes of arthropods, molluscs, and vertebrates). They also revert to the “orthodox” interpretation of the mammalian ear-ossicles, and in connection with this problem supply a valuable diagram of the temporal region of the skull in theromorphous reptiles for comparison with the mammalia. The book still neglects, to a great extent, palaeontological as well as embryological facts, but these are invoked where questions of morphology and relationship are discussed. Indeed, the last half of the volume comprises an excellent introduction to the comparative anatomy of vertebrates. As regards systems of classification, there is always room for differences of opinion, but we believe that most students of the Mollusca will object to the removal of the Chitons from association with Chaetoderma and Neomenia, and their replacement in the Gastropoda; while among the arthropods, the unnatural group of the “Myriapoda” is still retained, and appears in the same class with the insects and the peripatids-an altogether indefensible association. The introduction has been lengthened by two pages for the inclusion of a necessarily imperfect sketch of recent work on heredity. (1) Zoology: An Elementary Text-Book. By Dr. A. E. Shipley Dr. E. W. MacBride. Third edition. Pp. xx + 752.(Cambridge: At the University Press, 1915.) Price 12s. 6d. net. (2) Elementary Text-book of Economic Zoology and Entomology. By Prof. V. L. Kellogg Prof. R. W. Doane. Pp. x + 532.(New York: H. Holt and Co., 1915.) Price 1.50 dollars.

The Mnemic Theory of Heredity

THE reply to Prof. Dendy's comments upon my letter (NATURE, February 8, p. 482) is briefly as follows. The germ-cells are unicellular living organisms with a lifecycle of their own, part of which they pass in a metazoan individual. When they enter it, they are all in potentialities so many twins identical with this. For the time being its environment is theirs. The non-existent protoplasmic bridges need not be postulated. If the germ-cells could not “remember events in the past history of the race”, I fail to perceive how any developmental unfolding would be possible. The relation of the doctrine of acquired characters to the theory depends solely upon the embryological facts of the cycle of animal life.

The Middle Ear and Columella of Birds

ABSTRACT It may seem a supererogatory task to add to the pile of literature which deals with the ear-bone homologies a straightforward account of those anatomical and embryological facts which may be ascertained by the examination of such familiar types as the fowl and pigeon; but after a painstaking research into the literature of the Sauropsidau middle ear I have unwillingly concluded that such a course was desirable. Although this literature is voluminous there is no single description of any Suuropsidan type which from a modern standpoint can be considered at all complete ; that is to say, there is no account which describes in any one type— 1.The development and transformation of the auditory ossicles from the earliest procartilage stage up-war ds;2.The relations of the seventh nerve and chorda tympani to the ossicles at different stages of development.