differs from ordinary Lions and Tigers in having its claws so constructed that it cannot draw them back over the paws, though in every other respect they are like the claws of all the Cats. But while it has the Cat-like claw, its paws are like those of the Dog, and this singular combination of features is in direct relation to its habits, for it does not lie in wait and spring upon its prey like the Cat, but hunts it like the Dog.

While Genera themselves are, like Families, easily distinguished, the characters on which they are founded, like those of Families, are difficult to trace. There are often features belonging to these groups which attract the attention and suggest their association, though they are not those which may be truly considered generic characters. It is easy to distinguish the Foxes, for instance, by their bushy tail, and yet that is no true generic character; the collar of feathers round the neck of the Vultures leads us at once to separate them from the Eagles, but it is not the collar that truly marks the Genus, but rather the peculiar structure of the feathers which form it. No Bird has a more striking plumage than the Peacock, but it is not the appearance merely of its crest and spreading fan that constitutes the Genus, but the peculiar structure of the feathers. Thousands of examples might be quoted to show how easily Genera may

be singled out, named, and entered in our systems, without being duly characterized, and it is much to be lamented that there is no possibility of checking the loose work of this kind with which the annals of our science are daily flooded.

It would, of course, be quite inappropriate to present here any general revision of these groups; but I may present a few instances to illustrate the principle of their classification, and to show on what characters they are properly based. Among Reptiles, we find, for instance, that the Genera of our fresh-water Turtles differ from each other in the cut of their bill, in the arrangement of their scales, in the form of their claws, etc. Among Fishes, the different Genera included under the Family of Perches are distinguished by the arrangement of their teeth, by the serratures of their gill-covers and of the arch to which the pectoral fins are attached, by the nature and combination of the rays of their fins, by the structure of their scales, etc. Among Insects, the various Genera of the Butterflies differ in the combination of the little rods which sustain their wings, in the form and structure of their antennæ, of their feet, of the minute scales which cover their wings, etc. Among Crustacea, the Genera of Shrimps vary in the form of the claws, in the structure of the parts of the mouth, in the articulations of their feelers, etc. Among

Worms, the different Genera of the Leech Family are combined upon the form of the disks by which they attach themselves, upon the number and arrangement of their eyes, upon the structure of the hard parts with which the mouth is armed, etc. Among Cephalopods, the Family of Squids contains several Genera distinguished by the structure of the solid shield within the skin of the back, by the form and connection of their fins, by the structure of the suckers with which their arms are provided, by the form of their beak, etc. In every Class, we find throughout the Animal Kingdom that there is no sound basis for the discrimination of Genera except the details of their structure; but in order to define them accurately an extensive comparison of them is indispensable, and in characterizing them only such features should be enumerated as are truly generic; whereas, in the present superficial method of describing genera, features are frequently introduced which belong not only to the whole Family, but even to the whole Class which includes them.

CHAPTER X.

SPECIES AND BREEDS.

THERE remains but one more division of the Animal Kingdom for our consideration, the most limited of all in its circumscription, that of Species. It is with the study of this kind of group that naturalists generally begin their investigations. I believe, however, that the study of Species as the basis of a scientific education is a great mistake. It leads us to overrate the value of Species, and to believe that they exist in Nature in some different sense from the other groups; as if there were something more real and tangible in Species than in Genera, Families, Orders, Classes, or Branches. The truth is, that to study a vast number of Species without tracing the principles that combine them under more comprehensive groups is only to burden the mind with disconnected facts, and more may be learned by a faithful and careful comparison of a few Species than by a more cursory examination of a greater number. When one considers the immense number of Species already known, naturalists

might well despair of becoming acquainted with them all, were they not constructed on a few fundamental patterns, so that the study of one Species teaches us a great deal for all the rest. De Candolle, who was at the same time a great botanist and a great teacher, told me once that he could undertake to illustrate the fundamental principles of his science with the aid of a dozen plants judiciously selected, and that it was his unvarying practice to induce students to make a thorough study of a few minor groups of plants, in all their relations to one another, rather than to attempt to gain a superficial acquaintance with a large number of species. The powerful influence he has had upon the progress of Botany vouches for the correctness of his views. Indeed, every profound scholar knows that sound learning can be attained only by this method, and the study of Nature makes no exception to the rule.

I would therefore advise every student to select a few representatives from all the Classes, and to study these not only with reference to their specific characters, but as members also of a Genus, of a Family, of an Order, of a Class, and of a Branch. He will soon convince himself that Species have no more definite and real existence in Nature than all the other divisions of the Animal Kingdom, and that every animal is the representative of its Branch, Class, Order, Family,