Fig. 1.—Archæopteryx lithographicus.
The skull of the Archæopteryx is almost lost, but the leg, the foot, the pelvis, the shoulder-girdle, and the feathers, as far as their structure can be made out, are completely those of existing birds. On the other hand, the tail is very long. Two digits of the manus have curved claws, and, to all appearance, the metacarpal bones are quite free and disunited, exhibiting, according to Professor Huxley, closer approximation to the reptilian structure than any existing bird. Mr. Evans has even detected that the mandibles were provided with a few slender teeth.
On the other hand, the same writer points out certain peculiarities in the single reptile found also among the Solenhofen slates, which has been described and named Compsognathus longipes by the late Andreas Wagner. This reptile he declares "to be a still nearer approximation to the missing link between reptiles and birds," thus narrowing the gap between the two classes.
While we think it proper to point to these structural resemblances of one class of the animal creation to others very different in their external appearance, it is necessary to guard ourselves and our readers from adopting the inferences sometimes deduced from them; that "these infinitely diversified forms are merely the final terms in an immense series of changes which have been brought about in the course of immeasurable time, by the operation of causes more or less similar to those which are at work at the present day." Domestication and other causes have no doubt produced changes in the form of many animals; but none from which this inference can be drawn, except in the imagination of ingenious men who strain the facts to support a preconceived hypothesis. In spite of the innumerable forms which the pigeon assumes by cross-breeding and domestication, it still remains a pigeon; the dog is still a dog, and so with other animals. Nor does it seem to us to be necessary, or calculated to advance our knowledge in natural history, to form theories which can only disturb our existing systems without supplying a better. Systems are necessary for the purpose of arrangement and identification; but it should never be forgotten that all classifications are artificial—a framework or cabinet, into the partitions of which many facts may be stowed away, carefully docketed for future use. "Theories," says Le Vaillant, "are more easily made and more brilliant probably than observations; but it is by observation alone that science can be enriched." A bountiful Creator appears to have adopted one general plan in the organization of all the vertebrate creation; and, in order to facilitate their study, naturalists have divided them into classes, orders, and genera, formed on the differences which exist in the structure of their vital functions. The advantages of this are obvious, but it does not involve the necessity of fathoming what is unfathomable, of explaining what is to man inexplicable in the works of God.[2]
In previous volumes of this series[3] we have endeavoured to give the reader some general notions of the form, life, and manners of the branches of the animal kingdom known as Zoophytes, Mollusca, Articulata, and Pisces. We now continue the superior sub-kingdom (to which the fishes also belong) of the Vertebrated Animals, so called from the osseous skeleton which encircles their bodies, in which the vertebral column, surmounted by the cranium, its appendage, forms the principal part.
The presence of a solid frame in this series of animals admits of their attaining a size which is denied to any of the others. The skeleton being organized in such a manner as to give remarkable vigour and precision to all their movements.
In the vertebrated animals the nervous system is also more developed. There is, consequently, a more exquisite sensibility in them than in the classes whose history we have hitherto discussed. They possess five senses, more or less fully developed, a heart, a circulation, and their blood is red.
We have now to deal with a class advanced above that of fishes, that of Reptilia, which is divided as follows:—