Page:Popular Science Monthly Volume 43.djvu/720

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Vertebrate Embryology. A Text-book for Students and Practitioners. By A. Milnes Marshall, M. D., D. Sc, Professor in the Victoria University, etc. New York: G. P. Putnam's Sons. London: Smith, Elder & Co., 1893. Price, $6.

As the author truly states in his preface, most of the text-books of embryology aim rather at explaining the general progress of development within the several animal groups than at supplying complete descriptions of individual examples. Thus there have been no reasonably complete accounts of the development of the common frog or of the rabbit, while in human embryology so much is yet unknown that the descriptions and figures given in illustration of them are those of embryonic rabbits, pigs, chickens, or dogfish. As the results of recent investigations have shown that marked differences, both in the earlier and the later stages of development, may occur between allied genera and species, it may be perceived that this practice of illustrating human embryology by embryological types selected from the lower animals may be the cause of much confusion.

In preparing this volume the author has selected a few types to each of which a separate chapter is devoted. The first chapter gives a general account of the development of animals, including the structure, maturation, and fertilization of the egg, and a description of the early stages of the development of the embryo. We think the author has made a slight lapsus calami in the statement on page 13 that "after one spermatozoon has entered an egg others seem incapable of making their way in"; we judge that he intended to write "yolk" instead of egg, for spermatozoa have been found not only in the zona but in the perivitelline space. We believe that it is after the spermatozoon gains entrance into the yolk instead of the egg, as is stated, that the tail is lost. The theory of sex is too meagerly presented to afford the student any enlightenment, none of the more important theories being mentioned.

The second chapter is devoted to the amphioxus, giving a general account of the early and late embryonic development of this fish-like animal. In this chapter the author has followed the descriptions of Kowalevsky, Hatschek, Lankester, and Willey; and this animal has been selected as an introduction to vertebrate embryology because of the simplicity of its earlier developmental history as well as on account of the clew that this affords to the more complicated conditions occurring in the higher vertebrates.

The third chapter gives a general account of the development of the frog, the description of the processes of maturation and fertilization of the egg being based on O. Schultze's investigations, while the account of the early stages of development of the nervous, circulatory, digestive, and reproductive organs is based on the observations of the author and his pupils.

The fourth chapter gives a description of the development of the chick that is so familiar from the accounts given in most of the physiologies.

The fifth chapter gives an account of the development of the rabbit, the author following the accounts of Van Beneden, K├Âlliker, and Duval in his description of the processes of segmentation of the egg, of the formation of the blastodermic vesicle, and of the placenta. The descriptions of the later stages of development are based on his own observations.

The sixth and final chapter describes the development of the human embryo, and is, of course, to a large extent, based on the researches of His.

The author requests that human embryos of any age, but more particularly those of the first month or six weeks, be wrapped in cotton, placed in a bottle of strong alcohol, and sent to him at Owens College.

We note, especially in the earlier part of the book, a duplication of illustrations: thus Figures 1 and 45; 2 and 14; 3 and 46, 47, 48, 49, and 50; 4 and 97; 5 and 102; 6 and 103; 7 and 105; 8 and 25; and 9 and 26, are identical.

The book is clearly written in English rather than Anglicized German, and there is a most agreeable omission of German terms that mar the harmony of some of the recent works on embryology. Long quotations and discussions of mooted points are avoided, the author apparently seeking to present that