bers, presents all the essential marks of homogeneity. The chief character by which the Cirripedia are distinguished from the Entomostraca consists in their hermaphroditism, and Dr. Gerstaecker seems to entertain some doubt as to the accuracy of Mr. Darwin's observations of the occurrence of "complemental males" in some species. He adopts the opinion of Lilljeborg as to the Cirripedian nature of the curious parasitic Sacculina and its allies, and admits them into the system as forming a family, to which he gives the name of Suctoria, proposed for them by that author.

The Crustacea conclude Dr. Gerstaecker's portion of this Manual of Zoology, which, notwithstanding some minor defects, such as those which we have briefly indicated, has evidently been executed with great care and with a most conscientious desire to do full justice to his subject. It is of course easy to cavil at some portions of his system, but we must at the same time admit that he has produced a most successful general view of the vast series of Arthropod animals, while the generic types described as examples of the families are generally judiciously selected, and the chief facts in the life-history of the animals, especially those bearing upon systematic Zoology, are clearly, although of course very briefly depicted.

Dr. Carus' section of the work, occupying just one-third of the volume, strikes us as being rather slighter in its general execution; but when we consider the vast extent of systematic ground that he has had to run over in so short a space, and that the great extension of the Arthropod section has evidently necessitated a correspondingly increased compression of that devoted to the lower Invertebrata, we may excuse some little shortcomings.

Dr. Carus commences his work with the Rotatoria, which he regards as a class forming a sort of appendix to the Arthropoda, and under any circumstances they must be looked upon as constituting a sort of transition between those animals and the true Vermes. The author divides the Rotatoria into eight families, out of which he claims five as newly defined by himself, although three of them were certainly recognised and named long since, and admitted with very little difference of contents in Van der Hoeven's "Handbook."

The Vermes, although treated here as a primary section of the Animal Kingdom, are not regarded by Dr. Carus as constituting a distinct type, but only "as forms of that great series (Annulosa) which attains its climax in the Arthropoda." In this respect he differs from Vogt, who even allows the Mollusca to intervene between

his Vermes and Arthropoda. In his general view of the members of the group, however, he agrees pretty closely with Vogt, except that he excludes the Rotatoria and Gregarinæ and includes Sagitta.

The Vermes, according to Dr. Carus, form five classes—namely, Annulata, Gephyrea, Chaetognatha, Nematelminthes, and Platyelminthes. With regard to the first of these groups we need only say that the author closely follows Grube in his classificatiou, and that he has given a most careful analysis of the families and genera of the Ringed-worms. Here and there we find new family groups defined, and on p. 447 Dr. Carus proposes a new provisional section, Haloscolecina, with two families for the reception of the problematical genera Dero and Capitella and their allies.

The Gephyrea (Sipunculus and its allies) placed by many authors with the Holothuroidea among the Echinodermata form the second class of the Vermes in the system of Dr. Carus, who gives as his reason for referring them to this position that "although their organisation is not exhaustively known, the deficiency of calcification in the skin, the absence of the aquiferous system with its dilatable appendages, the decided bilateral symmetry, the bristles and other characters indicate their proper position to be amongst the Worms." (p. 452.) At the same time these curious creatures present many characters incompatible with their occupying a place even among the multifarious types of the Annelides, and perhaps the best course that can be adopted at present, is that followed by our author, of placing them in a distinct (provisional) group in the immediate vicinity of the Ringed-worms. Dr. Carus divides them into four families-namely, the Sternaspidea, Echiuridea, Sipunculidea and Priapulidea.

The Sagitte, which have the somewhat questionable honour of having been referred by different writers to no less than three of the great primary divisions of the animal kingdom, constitute Dr. Carus' third class of Vermes, the Chatognatha. It is hardly fair of the author, however, to ascribe to the late Edward Forbes the establishment of the Molluscous order Nucleobranchiata for the reception of these puzzling creatures, considering that that group was founded many years ago by De Blainville for the genera Carinaria and Firola, and that those Zoologists who referred Sagitta to such a position were led to do so by a very laudable desire to avoid establishing a new group for animals of which they knew next to nothing. In the present day Zoologists are, as stated by Dr. Carus, pretty well agreed that the

Sagittæ must occupy a place among the Vermes, but their precise position is still open to discussion. It is a question, however, whether Dr. Carus might not have done better towards producing a clear picture of this difficult branch of Zoology, had he divided his Vermes only into three great classes, of which the first might include the three groups to which we have already adverted. The differences between his Annulata, Gephyrea, and Chaetognatha are hardly of the value of those upon which classes of animals are generally founded, and by including the constituents of the three groups as orders of a single class, their stronger mutual affinity as compared with that existing between them and the parasitic Nematelminthes and Platyelminthes would be better expressed.

Of the former of these parasitic classes we need say but little,— the author adopts the generally received classification of the Nematoid worms and follows Diesing for the most part in the subordinate groups. But in regard to the Platyelminthes he reverts to the old, and it seems to us erroneous, plan of including the Turbellaria in the same class with the parasitic Trematode and Cestoid worms, a proceeding from which we should have thought he might have been restrained even by the difficulty which he has evidently experienced in framing his definition of the class. The Turbellaria are manifestly of a higher type than the Trematode worms with which they are here associated, and approach in many respects to the lower forms of the Hirudinea, most of which, like the majority of the Turbellaria, are hermaphrodite. Moreover, in the Turbellaria we find no trace of that complicated system of digenesis which prevails, as far as we know, almost throughout the Trematode and Cestoid worms, the so-called alternation of generations in the Nemertina being of a very dissimilar nature.

The classification of the Turbellaria here adopted is founded upon the systems proposed by Keferstein, Max Schultze, and Schmarda, with the introduction of some groups established by Mr. Stimpson in his "Prodromus," published in the Proceedings of the Philadelphian Academy for 1857. The Trematoda and Cestodea are arranged in accordance with the latest systematic views of Van Beneden.

It is unfortunate with respect to furnishing the student with a clear view of the primary grouping of the animal kingdom, that the five main sections described in this volume are represented typographically as of equal value, although three of them are regarded by the authors as going to make up the great division of the Annulosa.

This circumstance may be of little consequence to the advanced student, who forms his own conclusions upon classification, and views such books as this by the light of an intelligent criticism, but to the beginner it must be not a little puzzling to find that groups treated apparently as equivalent are really of very different value, and that what is spoken of as a class in one page is subsequently divided into classes. Thus the Arthropoda and Vermes which stand as primary heads in this book, are regarded by Dr. Carus as sections of the Annulosa, to which great division of the animal kingdom he likewise refers the third main section (Echinodermata); and both the Vermes and Echinodermata are mentioned as classes (pp. 422 and 485) whilst their subdivisions are also described as classes. And again these groups appear as if equivalent to the Colenterata and Protozoa which follow them, but which are universally allowed to be of higher systematic rank. It may be thought that such remarks savour of hypercriticism, but let any one look back to the period of his first steps in science and he will hardly be inclined to make light of such a fault as want of method in a student's manual. It is to be hoped in the interests of a sound zoological system, that when the first volume of this "Handbook" makes its appearance a table of classification showing the true relations and subordinations of the groups may form part of its contents. The Echinodermata

are divided by Dr. Carus into the usual four orders-viz., Holothurioidea, Echinoidea, Asterioidea, and Crinoidea.

With regard to the classification of the Cœlenterata, which are adopted here as constituting a primary division, our author differs somewhat from the views advocated by Huxley. Recognizing the two types of structure represented by the Actinozoa and Hydrozoa of that distinguished zoologist, he yet divides the Colenterata into three classes, considering the characters presented by the Ctenophora to be of sufficient value to entitle them to rank as a distinct class. In this he is probably right, as, notwithstanding the unmistakeable resemblance of some of the Ctenophora to such Actinian forms as Ilyanthus and Philomedusa, the bilateral symmetry of the body, the nature of the tentacles when present, the peculiarities of the canalsystem, the degree of development of the nervous system, and the ciliated paddles by which the free movements of the animals are effected, would seem to entitle them to rank as a group apart from the Anthozoa. The latter are described by Dr. Carus under the name of Polypi, and his classification of them is founded upon that

established by Milne-Edwards in the well-known "Histoire Naturelle des Coralliaires "except that he has removed the Tabulata and Rugosa of Milne-Edwards, chiefly formed of Fossil corals, to the place assigned to them among the Hydrozoa by the researches of Agassiz.

In his treatment of the complicated phenomena of the life-history of the Hydrozoa and his appreciation of their bearing upon the system, Dr. Carus seems to us to have been very happy. His first order consists of the Medusa (the Steganophthalmata of Forbes, the Lucernaride of Huxley, less Lucernaria), his second of the Lucernaria, the Calycozoa of Leuckart. For his third and last order he adopts Vogt's name of Hydromedusa, giving it, however, a sense very different from that in which its author used it. The Hydromedusæ of Dr. Carus include two groups, the Siphonophora and the Hydroidea; the former described in general accordance with Professor Huxley's views, except that the main division into Calycophorida and Physophorida is rejected; the latter including the whole of the Hydroid Polypes and Naked-eyed Medusæ of former authors. Of the sexual Medusoids, whether set free from fixed Polype-forms or produced directly from the ova of similar creatures, an analysis is given in accordance with Gegenbaur's "System der Medusen," but this is only preliminary to the systematic résumé, in which the author endeavours to represent the multifarious relations of these perplexing creatures. In this the Hydroidea are divided into two sections, Haplomorpha and Diplomorpha, the former including those Medusoid forms (Geryonidæ, Trachynemidæ, Æquoreidæ, and Aeginida) which are developed directly from the ovum without metagenesis,—and the latter, the Polypoid forms which produce either free sexual zooids, or attached and usually more or less Medusoid buds. To the latter group Dr. Carus refers the Tabulate and Rugose Corals, of course provisionally, forming with them a section to which he gives the name of Lithydrodea; his other sections of Diplomorpha are called Skenotoka (Sertularian and Campanularian polypes) and Gymnotoka (Tubularidæ, Corynidae, with Hydra).

That there may be defects in this system can hardly be denied, but it seems to us to approach more nearly towards the production of a true picture of the natural relations of the Hydrozoa than any of its predecessors.

Indeed as we approach the lower confines of the Animal Kingdom, or of any of its great divisions, a certain difficulty of satisfactorily classifying the objects under consideration seems always to meet us,