CURRENT LITERATURE.
The Apodidx : a Morphological Study. By Henry Meyners Bernard, M.A. Cantab. "Nature Series." (Macmillan and Co.) —A. work like the present strikingly illustrates the enormous change which has come over the ideas and methods of biology
since the general acceptance by scientific men of the fundamental ideas enunciated in Darwin's "Origin of Species." Fifty years ago, inquiries into the relationships between species could have had only an academic value; nor had any lines for profitable research in such a direction then been laid down. But now that naturalists regard species, not as a congeries of isolated entities, but as the extremities of the ramifying branches of a vast tree, they are eagerly searching in all directions to find the connecting links, past and present, between groups now more or less widely separated. At first sight, it might appear that there is but little resemblance between a worm and a crab or a lobster, except that they belong to the great class of Annulosa, or jointed animals. Nevertheless, there are sufficient points of resemblance between the Annelida and Crustacea to lead naturalists to seek for connecting links between them ; but hitherto without success. Mr. Bernard's studies in the anatomy of the Apodithe (a small group of Crustacea usually met with in pools and ditches formed by rain-water), however, led him to regard these animals as closely related to the carnivorous Annelids. Pursuing the subject further, he has arrived at the conclusion that Apus is actually derived from a carnivorous Annelid which acquired the habit of browsing, with the first five segments of the body bent round, which finally became fused together into a new form of head. Such an explanation seems at first sight almost too simple to be true; but the author has followed up his inquiries by investigations into the structure of the larval Nauplius form of Crustacea, and of the more archaic recent, and fossil adult forms, such as Limulus and the Trilobites, and has finally been led to derive the origin of the whole class Crustacea from his bent Annelid ; and further, in a chapter on the curious transitional form Peripatns,he claims an analogous origin (but from an unbent Annelid) for the Tracheate likewise. It is well known that the best authorities consider that the head of an insect is similarly formed by the fusion of several segments, or somites. The details of Mr. Bernard's researches (as far as he has been able to state them within the limits of a small volume) can only be fully appreciated by specialists ; but his observations will nevertheless be read with interest by all who care to follow the progress of philosophical natural history. If his conclusions should prove well established, they may form the basis for a new and almost infinitely extended series of observations on the simple but highly suggestive theory which he has brought for- ward in this interesting little book.
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