the unity of this design. That is, it is carried out in all parts of the bodily organization. Those animals intended to live on dry ground have none of the structure, or organs, or members pecu- liarly suited to aquatic animals. The lion, tiger, ox, horse, etc., have neither the gills, the scales, the fins, nor the rudder-like tail of the fish. All parts of the animal harmonize. They are all related and adapted to one and the same end. The body of the fish is shaped so as to cleave the water with the least resistance ; its fins are oars, its tail is adapted both for propulsion and guidance ; its breathing apparatus is suited to separate the air from water ; its digestive organs are adapted to the assimilation of the kind of food furnished by the element in which it lives. The same thing is ob- viously true of all terrestrial animals. Besides this general adapta- tion of animals for living in the air, in the water, and on the dry ground, there are innumerable more specific adaptations suiting the species of fishes, birds, and land animals for the particular modes of life for which they are designed. Some are intended to be carnivorous, and their bodies are harmoniously constructed with a view to that end. Others are intended to live on herbs, and in them we find everything adapted for that purpose. This adapta- tion refers to numerous and varied purposes. Hence the genera and the species of animals belonging to the different departments, classes, orders, and families into which the animal kingdom is di- vided, are exceedingly numerous, and each has its distinctive cor- poreal organization indicative of the specific end it is intended to subserve. So minute, and so fixed is the plan on which each species of animal is constructed, that a skilful naturalist, from the examination of a single bone, can tell not only the family, or genus, but the very species to which it belongs. Agassiz has, from a single scale of a fish, delineated its whole body as accurately as though the living animal had been photographed. And the cor- rectness of his delineation has been afterwards verified by the dis- covery of a perfect specimen of the species portrayed. Now, the important principle deducible from these admitted facts is, that no diversity of colour, form, proportion, structure, etc., not indicative of design, or not proving a difference in the immaterial principle which determines the nature of the animal, can of itself be admitted as proof of diversity of species. The Italian greyhound and the English mastiff differ in all the respects just mentioned. The Shet- land pony, the London dray-horse, and the Arabian or the Barb exhibit similar striking diversities. But when they come to be anatomically examined, it is found that they are constructed 071 the
b4 PART n. Ch. IV. -UNITr OF THE HUMA:M RACE.
same plan. The bony structures, the distribution of the nerves, muscles, and blood-vessels, are all expressive of the same general intention. Hence, naturalists refer these varieties to the same spe- cies. And the correctness of this conclusion is confirmed by every other criterion of the identity of species. While it is admitted that such diversities do exist in the varieties belonging to the same spe- cies of the lower animals, it is surprising that far less diversities of the same kind among the varieties of the human family should be insisted upon, as evidence of difference of species. The wild dog wherever found is nearly of the same colour, and the same size, with ears, limbs and tail of the same form, and yet how endless are the permanent varieties derived from that original stock. It is well known that such varieties can be artificially produced. By skilful breeding almost any peculiarity of form, colour, or struc- ture within the limits of the original idea of the species, can be produced and perpetuated ; as is seen in the different breeds of horses, cattle, and sheep found even in so restricted a field of oper- ation as Great Britain. It is certain, therefore, that no diversity of an external or material character, not indicative of diversity of design, plan, and intention can properly be assumed as indicative of diversity of species. The presence of a skin connecting the toes or claws of a bird, is in itself a comparatively small affair. It is insignificant as to the amount of material expended, and as to the effect on the general appearance compared to the points of differ- ence between the greyhound and the mastiff, and yet it is indica- tive of design. It indicates that the animal is intended to live in the water ; and everything else in its structure and nature is found to correspond with that intention. A small difference of structure indicative of design will prove difference of species, when much greater differences not thus indicative are perfectly consistent with unity of species.
Physiological Argument.
The second method of determining the identity of the imma- terial principle in which the idea of species resides, is the exami- nation of its ^v'crt?, or its physiology. To this department belongs all that relates to enervation or the distribution of the nerve power ; to the circulation of the blood ; to respiration ; to calorifi- cation or production of animal heat ; to the distribution of the mus- cles voluntary and involuntary ; to the processes of digestion, assim ilation, propagation, etc., etc. As to this point it is to be observed, (1.) That the ^vVis, or animal nature, is always in accordance with