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occur only in one or the other, and can not survive any diminution or increase of the saltness of the water they live in. The simple reason of this phenomenon is the fact that the life of an animal depends not merely on the influence of the external conditions, but on the reaction of its own organization. If we transfer a stickleback directly from fresh to salt water, and leave it there for days or weeks, it will not perish if it be supplied with sufficient food. But, if at the same time we place one of the common fresh-water mussels in sea-water, it will soon die, sometimes in a few hours. The remarkable difference in the behavior of these two creatures is easily explained by the following hypothesis: In both animals the salt water is transmitted through the skin to the tissues of the body; but this takes place to a much greater extent in the mussel than in the fish, and thus injures it, while the fish can bear the same quantity of salt it has absorbed. If our migratory fishes, as the salmon, had as great an affinity for the salt of the sea-water as the mussels have, they would soon cease to exist, or would have to become adapted to live wholly in fresh water. Thus every change in the conditions of existence influences different animals in different ways. The problem, then, is to investigate more accurately these different effects of changed conditions.

Professor Semper's twelve lectures before the Lowell Institute form the twelve chapters of his book. The considerations here presented are put forward in the first or introductory chapter, in which he defines his point of view, and the plan of the discussion. The work is divided into two parts, the first being devoted to "The Influence of Inanimate Surroundings," and the second to "The Influence of Living Surroundings." Chapter II takes up "The Influence of Food"; III, "The Influence of Light"; IV, "The Influence of Temperature"; V, "The Influence of Stagnant Water"; VI, "The Influence of Still Atmosphere"; VII and VIII, "The Influence of Water in Motion"; IX, "Currents as a means of extending or hindering the Distribution of Species"; X, "A Few Remarks on the Influence of Other Conditions of Existence"; XI, "The Transforming Influence of Living Organisms on Animals"; XII, "The Selective Influence of Living Organisms on Animals." Appended to the volume are sixty pages of valuable notes, followed by a copious alphabetical index.

Annual Report of the Chief of Engineers, United States Army. Pp. 264.

The report describes what was done during the year ending June 30, 1880, and what was needed to be done for the seacoast and lake frontier defenses of the country, and for the improvement of the rivers and harbors of the whole country; and records the progress of the special work and of the surveys assigned to the corps of engineers. Several maps of Pacific States and of the survey of the Mississippi River, and lake charts, have been published, and an outline map of the territory west of the Mississippi River, on a scale of 12000000 is in preparation.

Life and her Children; Glimpses of Animal Life from the Amœba to the Insects. By Arabella B. Buckley, New York: D. Appleton & Co. 1880. Price, $1.50.

After light came life, and with that life there came its two great functions—growth and development. With the simplest as with the most complex forms there is the same eager race to be run, to increase in size, to multiply, and, thus replenishing this earth, to die. "Life and her Children" is a praiseworthy and admirable attempt to tell us something of the Children that Life sends forth, and of their history. Its main object is to acquaint young people with the structure and habits of the lower forms of life; but in our deliberate judgment it will do a great deal more. None will read its introductory chapter without advantage, and few will read the volume through without enjoyment. Within its narrow limits of three hundred small pages no candid reader would expect to find all the details that might be wished for, or all the illustrations that might be desired. What constitutes the book's chief charm is the marvelously simple yet quite scientific style which runs through it, the food for thought and future study which it affords, and the truly philosophic glow which lights up its every page. The volume gives a general account of Life's Simplest Children, the Protozoa. The word "slime" does not seem to us quite a happy term by which to designate the living protoplasm of these creatures; this word conveys the idea of a something adhesive or glutinous, or of a something thrown off a living organism—a something without a structure (sordies, eluvies)—and there seems somewhat of a "contempt for nature," a thought certainly never present in the au-