40. _Delphinus_, the dolphin: 3 species. Including a few additional species mentioned in the appendix to the third volume, and the Mantissa of 1771, the number of Mammalia known to Linnaeus was about 230. At the present day, more than 1000 species are described. The second class, that of BIRDS, is divided by him into six orders, the essential characters of which are derived from the bill and feet, as follows:-- I. ACCIPITRES: _Birds of Prey_. The bill more or less curved, the upper mandible dilated or armed with a tooth-like process near the tip; the feet short, robust, with acute hooked claws. II. PICAE. The bill cultriform, with the back convex; the feet short, rather strong. III. ANSERES: _Web-footed Birds_. The bill smooth, covered with epidermis, enlarged at the tip; the toes united by a web, the legs compressed and short. IV. GRALLAE: _Waders_. The bill somewhat cylindrical; the feet long, bare above the knee, and formed for wading. V. GALLINAE: _Gallinaceous Birds_. Bill convex, the upper mandible arched over the lower, the nostrils arched with a cartilaginous membrane. Feet with the toes separated, and rough beneath. VI. PASSERES: _Small Birds_. Bill conical, sharp pointed; feet slender, the toes separated. It may here be remarked, that this arrangement is liable to many objections, and especially because the characters given to the orders are totally inapplicable to many species contained in them. Thus, the vultures, which belong to the first order, have no projecting processes on the upper mandible; the parrots, which are referred to the second, have the bill hooked, not cultriform, and bear no resemblance to the other species; among the Anseres, which are characterized as having the bill smooth, covered with epidermis, and enlarged at the tip, are the gannet with a bare pointed bill, the divers, the terns, and the gulls, with bills not at all answering to the description given; among the Grallae with a cylindrical bill, are the ostrich with a short depressed one, the boatbill with one resembling a boat, the spoonbill, the heron, the flamingo, and others, whose bills differ from each other as much as from that of the snipes and curlews; the character given to the bill of the Gallinae agrees with that of many Passeres; and, lastly, the wagtail, the swallow, the tit, the robin, and a multitude of other small birds, have bills extremely unlike those of the goldfinch, bunting, and crossbill, which are referred to the same order. We mention these circumstances, not for the purpose of detracting from the merit of Linnaeus, but simply because we are persuaded that many of his generalizations are extremely incorrect, as are in many respects those of all his predecessors, and even of the ablest philosophers of the present age. It is absurd to attempt to thrust the objects of nature into squares or circles, or enclosures of any other form.