The fourth edition of Professor T. R. Jones's 'Outline' may be taken as an evidence that his work is still in demand, notwithstanding the formidable rivalry of Professor Rolleston's recent work on the same subject addressed to the same class of readers. Perhaps the less formal and technical style of treatment may be an attraction to some students of comparative anatomy. Men who give themselves to the study of what are called the descriptive sciences, have often had their attention directed to them in the first instance by their pictorial attractions, and they retain a certain license in dealing with these branches of learning which neither instructors nor students of the more exact sciences would permit themselves. Professor R. Jones has taken his full poetical license, and the parts of the work which display it in the highest degree are peculiarly his own. There is no objection to this mode of treatment so long as it does not take off the attention of the learners from the more general and harder parts of the subject. But the comparative anatomy of the whole animal kingdom is so vast that if the author allows himself to run after the descriptions which are of most interest, his presentation of the whole subject is likely to be fragmentary and imperfect. The previous editions of this work have stood almost alone as popular elementary manuals, and this edition contains very few additions to the former ones--such only, in fact, as have been forced on the author. He has designedly hung in the rearward of the science, and is a collator rather than a critic or an investigator. Thus he cannot resist the claims of the Cælenerata to be ranked as a sub-kingdom, and the adoption of Free and Leuckart's classification has compelled him to transpose the positions of the Anthozoa and Hydrozoa. This, however, is almost his only classificatory innovation. By a convenient conservation he still retains the Cirrepedia as a distinct class, while the Rotifera are placed under the Crustacea. The Brachiopoda are still interposed between the Conchifera and Gasteropoda. The Amphibians are not separated from the Reptilia. These antiquated ideas of classification are to be regretted; but inasmuch as the object of the volume is to describe, rather than to classify, they need not be condemned as erroneous. When treating of the vertebrate classes, the author becomes little more than the interpreter of Professor R. Owen, and we deplore that a theory of the elements of a vertebra which has never been generally adopted by the scientific world should be introduced into a student's book without criticism or comment. The principal additions which appear in this edition are pictorial, and the new pictures are, for the most part, illustrative of natural history rather than of anatomy. An exception to this is, however, found in the introduction of Mr. Albany Harcock's very instructive delineation of Waldheimia Australis.