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SCIENTIFIC LITERATURE.

times, and he indicates the possession of something like 50 additional forms.

Almost 100 pages are devoted to the peculiarities of mosquitoes in all stages, and to the methods to be era-! ployed in studying them. The mouth: structures are explained in the conventional way and the matter of food is gone into somewhat in detail. Of course comparatively few mosquitoes ever get a meal of blood, and yet it would seem that for some species such a meal is an essential preliminary to reproduction. All sorts of vertebrates may be attacked, even fish and reptilia, and invertebrates seem almost as susceptible. The males, being unable to puncture either animal or vegetable tissue, are confined to a diet of prepared liquids—nectar and the like—but do not despise others, like beer and wine, when they can get them.

To mosquitoes as disease carriers only a few pages are devoted; the author referring to such writings as Ross's, Grassi's, Nuttall's and others. He specifically discusses 'Malaria,' filariasis and yellow fever, though adding nothing from personal observation. Birds and probably some animals suffer from diseases carried by these insects and usually only one, or a small group of species, acts in the transmission. Thus the species of Anopheles, in America at least, is responsible for the distribution of malarial troubles, while Stegomyia appears to do as much for yellow fever.

Mr. Theobald emphasizes the character of the scales on certain portions of the head, wing and body, which assists in separating species. This brings into play the microscope and, practically, that instrument must be resorted to for final determinations in some instances.

It is altogether a very interesting and useful book to the entomologist who wishes to learn what has been done in this family and who has done it. The plates are too highly colored and the figures are, therefore, misleading. The text figures, illustrating structural details, are as a whole only fair, though the point to be illustrated is always well brought out. The book maker's work is well done, and so is the printer's, while a good index adds materially to the facility with which the book may be used by the reader.

MECHANICS.

An 'Elementary Treatise on Theoretical Mechanics' by Professor W. Woolsey Johnson (Wiley and Sons, New York) is far from elementary, as the reader is supposed to have a good knowledge of differential and integral calculus. The laws of nature are, however, quite independent of any system of mathematics, and many of those discussed in this volume might be easily treated by elementary algebra and geometry. There can be no objection to the use of the calculus if its demonstrations are simpler than those of common methods, but the combination of difficult mathematics with difficult subject-matter should be avoided in an elementary text-book. The plan of the book is that usual in this subject, forces being discussed at much length, in connection with the time-rate of space or velocity, before the subject of work or energy is taken up. This plan follows the historical line of development, but it is questionable whether it is the best method for the student or for getting at practical solutions. The book contains no unsound doctrine, is concisely written in a scholarly tone, and is an able presentation of the subject under the plan adopted.