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sented by so great a name no sacrifice was too great.

We are nearly at the end of our space, without, unfortunately, being nearly at the end of our subject. The travels of Mr. Youmans in England and on the continent of Europe, sometimes in the company of Spencer; his correspondence with members of his family in this country; his labors in arranging for the publication of the International Scientific Series, in connection with which he visited Paris, Berlin, and Leipsic, and came into personal relations with the leading savants of France and Germany; finally, his establishment of The Popular Science Monthly, chiefly on the strength of a series of original articles by Spencer, on The Study of Sociology, would admit of extensive and interesting treatment; but for all this we must refer our readers to the book itself. The aim of this notice has been to indicate to the many who knew Prof. Youmans only by name what manner of man he was, and what services he rendered in the cause of intellectual progress. Prof. Fiske, with the skill of an accomplished writer and the sympathy of an intimate friend and most sincere admirer, has given the finer as well as the broader lineaments of his character in a manner that leaves little to be desired. That so energetic a worker, with so capable a brain and so large a heart, should have died at the comparatively early age of sixty-five is a matter for profound regret, particularly as we are compelled to attribute it to the same want of care for his general health and over-devotion to work which brought on, and then aggravated, his early trouble with his eyes. As a writer Prof. Youmans had a style of his own, full of nervous force and grace—a style ample and rich, and yet admirably precise. Some of his essays are published as an appendix to the biography, and form most interesting and instructive reading. From these his dominant ideas and purposes may be gathered; and no one can read many pages without seeing and feeling that here was no intellectual dilettante, but a man with a mission, and that the lofty one of dissipating ignorance and prejudice, spreading the light of science, and preparing the way for those "nobler modes of life" of which seers have prophesied and poets sung.

The Genus Salpa. A Monograph, with Fifty-seven Plates. By William K. Brooks, Ph. D., LL. D. With a supplementary Paper by Maynard M. Metcalf. Memoirs from the Biological Laboratory of the Johns Hopkins University. Vol. II. Baltimore, 1893. Price, $7.50.

This bulky quarto, with its companion volume of fifty-seven plates, is a monumental work. It is the result of years of concentrated effort, and is a credit to American science.

The subject of the investigation is a pelagic or free-swimming Ascidian, confined to the high seas, and exceptional even in a group whose larvæ are plainly allied to vertebrates, while the adults have lost nearly every resemblance to their vertebrate allies by the degeneration and loss of their vertebrate features. Salpa is aptly described by Prof. Brooks as a transparent swimming Tunicate, which in effect is "an enormous pharynx which swims through the water, gulping in great mouthfuls at each contraction of its muscles." Happily the supply of radiolarian and diatom food is unlimited, and hence Salpæ multiply in immense profusion and with astonishing rapidity.

Salpæ under favoring conditions of food, and perhaps other physical causes not discussed by the author, reproduce both sexually and asexually. Each species has two generations in its life-cycle, known as the solitary generation and the aggregated generation. Chamisso, the poet, novelist, and biologist, first discovered this. The solitary salpa is born from an egg which is carried within the body of the aggregated salpa, whose blood nourishes the embryo during its development by means of a nutritive placenta. On the other hand, the aggregated or chain salpa are produced asexually by budding from the body of the solitary salpa.

This placenta, as Brooks shows, contrary to the views of some writers, has only a superficial resemblance to the fœtal organ of the mammals; it is an independent structure, being in the salpa only of use in conveying food to the embryo. This food has been discovered by the author to be great placenta cells which migrate from the body of the chain salpa into the body cavity of the embryo. Hence the embryo salpa stands in a much more direct relation to the external world than the mammalian embryo.