Vertebrate

“ Let me call your attention to those vertebrate animals which are most familiar to you, such as mammals, birds, and reptiles. At the present day, these groups of animals are perfectly well-defined from one another. We know of no animal now living which, in any sense, is intermediate between the mammal and the bird, or between the bird and the reptile; but, on the contrary, there are many very distinct anatomical peculiarities, well-defined marks, by which the mammal is separated from the bird, and the bird from the reptile. ”

“ After noticing the remarkable fact that all vertebrates having limbs have four, or the rudiments of them, and no more. Science predicts with the repose of conscious systematic truth, derived from this doctrine of segmental genesis, that no vertebrate animal, nor the remains of any, ever will be found, on the earth, or in the waters under the earth, or in its caverns or quarries, having more than these four homologous appendages—and these always dermal. ”

“ Special Homology of Vertebrate Limbs.—It would lead us much too far into unfamiliar technicalities to take up the whole skeleton. We select the limbs, both because their general structure is more familiar, and because in them the two fundamental ideas of essential identity and of adaptive modification are both admirably illustrated. The reason of this is, that it is by the limbs that the organism chiefly reacts on the environment, and is modified by it. ”

“ The head, too, which bears these organs of special sense, is more obviously marked out from the neck and body than is the case with the duller creatures occupying the lower branches of the Vertebrate stem. ”

“ Not only has an upward progress taken place in animals as a whole, but also in the tissues themselves a similar evolution is apparent, and the evidence shows that the vertebrate tissues resemble more closely those of the arthropod than of any other invertebrate group. ”

“ All morphologists arrive at the firm conviction that all vertebrata, from the Amphioxus upwards to man himself, all fishes, amphibia, reptiles, birds, and mammals, descend originally from a single vertebrate ancestor, for we cannot imagine that all the different and highly complicated conditions of life which, through a long series of processes or stages of development, led to the typical formation of a vertebrate, have accidentally happened together more than once in the course of the earth's history. ”

“ This vertebral column, as it is called, is distinctive of all vertebrates. Within its bony protection lies the delicate central nervous system, and to this column are attached the big bones of the legs and arms. The vertebrate animals deserve more of our attention than other forms of life because man himself is a vertebrate. ”

“ If the problem of vertebrate origin be considered from the wide point of view of comparative anatomy, it becomes no more difficult nor remarkable than the differentiation of any other type amongst simple, marine, unsegmented, or little segmented, wormlike creatures. ”

“ Is the human species a unique kind of vertebrate, or does it find a place in one of these classes? The occurrence of hair, of a four-chambered heart which propels warm blood, of mammary glands, and of other systematic characters marks this species as a kind of mammal and not as a vertebrate in a section by itself. ”

“ He must elect whether he will trust his interpretation to the soft organs, which among existing animals never vary their type in the great classes of vertebrate animals, and on which the animal is defined as something distinct from its envelope the skeleton and its appendages the limbs, or whether he will ignore them. ”

“ In the vertebrate body, however, the combination of organs attains to the highest development, in striking contrast with that of the class we have previously considered, the Invertebrata, the animal kingdom being divided into Vertebrates and Invertebrates. ”

“ During the first stages of their formation, all the embryos of vertebrate animals present merely the simplest and most general delineations of the type of a vertebrate; hence it is that they resemble each other so much as to render it very difficult to distinguish them. The fish, the reptile, the bird, the mammal, and man are at first the simplest expression of a type common to all ”

“ So the vertebrate must forever remain a vertebrate, and the articulate forever an articulate. Were they both evolved from the same unit? We are anxious to know, how from a pulpy mass of flesh, from a moneron, a creature of one substance, vertebrates were evolved. We would like to know, also, how a creature of more than one substance could be evolved from a creature of one substance without more being gotten out of the thing than there was in it. Here spontaneous generation passes into a wreck. ”

“ In order to find out the origin of vertebrates, inquire, in the first place, of the vertebrate itself.
Importance of the Central Nervous System.
Does the history of evolution pick out any particular organ or group of organs as more necessary than another for upward progress? If so, it is upon that organ or group of organs that special stress must be laid. ”

“ The above features are highly important, and will always prove quite sufficient to enable us to decide whether any particular animal is a vertebrate or an invertebrate, for it will be remembered that the body of the latter has only one cavity, containing the nervous system as well as the viscera, and that the nervous system is commonly placed along the ventral side, but never along the dorsal. ”

“ That which is true of the limbs, is also true of all the organs; and it is on this ground that we speak of the vertebrate type. From fish to man one common plan of structure prevails; and the presence of a backbone is the index by which to recognize this plan. ”

“ An abundance of the most interesting examples of rudimentary organs is furnished by Comparative Osteology, or the study of the skeletons of vertebrate animals, one of the most attractive branches of Comparative Anatomy. In most of the vertebrate animals we find two pairs of limbs on the body, a pair of fore-legs and a pair of hind-legs. ”

“ Thus, in Fishes, the first changes consist in the segmentation of the vitellus and the formation of a germ, processes which are common to all classes of animals. Then the dorsal furrow, characteristic of the Vertebrate, appears—the brain, the organs of the senses; at a later period are formed the intestine, the limbs, and the permanent form of the respiratory organs, from which the class is recognised with certainty. ”

“ Through the study of comparative anatomy, the fact has been discovered that the individuals composing the various orders of the great vertebrate series are all moulded “on the same general plan”; that up to a certain stage in the development of the several germs—for instance those of the man, the ape, the horse, the dog, etc.,—they are not distinguishable the one from the other, and that it is only at a later stage of development that they take on the peculiarities belonging to their own special kind. ”

“ The bony structure of man classes him as a vertebrate; the mode of suckling his young classes him as a mammal; his blood, his muscles, and his nerves, the structure of his heart with its veins and arteries, his lungs and his whole respiratory and circulatory systems, all closely correspond to those of other mammals, and are often almost identical with them. ”

“ But, after all, it is not of the essence of the vertebrate type to have the trunk and the abdomen attached at definite and invariable distances along the vertebral column—that is a notion surviving from the anatomy which made man its type. ”

“ Now, if we go down further in the system below the mammals, and find that even the wings of birds, the fore feet of reptiles and amphibious animals, are composed of essentially the same bones as the arms of man and the fore legs of the other mammals, we can, from this circumstance alone, with perfect certainty, infer the common origin of all these vertebrate animals. ”

“ We have shown that the general structure of all vertebrates is precisely what it would be if they all had come from one primal vertebrate form, and that of all articulates what it would be if all had come from one primal articulate form. ”

“ The differences between the Mammals and the reptiles and birds are so important and characteristic that we can assume with complete confidence this division of the vertebrate stem at the commencement of the development of the Amniotes. ”

“ All the mammals, from the lowest monotremes and marsupials to the ape and man, have a large number of striking characteristics in common, and these distinguish them from all other vertebrates: the hair and glands of the skin, the feeding of the young with the mother's milk, the peculiar formation of the lower jaw and the ear-bones connected therewith, and other features in the structure of the skull ”

“ The oldest fossil remains of vertebrate animals known to us belong to the lowest class, that of Fishes. Upon these there followed later more perfect Amphibious animals, then Reptiles, and lastly, at a much later period, the most highly organized classes of vertebrate animals, Birds and Mammals. ”

“ These are the people whose backbones remain cartilaginous all their lives long, as do those of certain other vertebrate animals,—the sturgeons, for instance. A good many poets must be classed with this group of vertebrates. ”

“ For example, among the land vertebrates the feet, which are associated with the structure of the limbs and trunk, may take one of many lines of adaptation to different media or habitats, either aquatic, terrestrial, arboreal or aerial; while the teeth, which are associated with the structure of the skull and jaws, also may take one of many lines of adaptation to different kinds of food or modes of feeding, whether herbivorous, insectivorous or carnivorous. ”

“ Animals are primarily classed in great divisions, based on the general characters which differentiate them most. These divisions, or branches, allow of their being so grouped that in each of them we find united the individuals whose general structure is uniform; and under the name of vertebrates are included man and the animals with which our studies will be occupied. The vertebrates, as the name indicates, are recognised by the presence of an interior skeleton formed by a central axis, the vertebral column, round which the other parts of the skeleton are arranged. ”

“ Among the whole of the invertebrates at present living on the earth, is there any sign of an internal cartilaginous skeleton that will give a direct clue to the origin of the primitive vertebrate skeleton? ”

“ The method of division, the formation of the primitive stomach and body-cavity, and the origin of the nervous system are identical, and a stage is attained in which thee young organism displays—or else simulates in an altogether inexplicable way—vertebrate characteristics. ”

“ To the first of these man himself belongs, and it is now admitted that the best and most practical way to acquire a knowledge of human physiology, anatomy, and development, is by studying the comparative physiology, anatomy, and embryology of vertebrates. Also, because our domestic animals belong to this group, with many of our friends among the birds, snakes, lizards, salamanders, toads, and fishes, it deserves special study. To the second branch belong the crab-like animals, the myriad-legged forms, those which are spider-like, and true insects, which are the highest of their branch. ”

“ All vertebrates have the same typical form. Take off the skins from some dozen air-breathing vertebrates, place the bodies in an upright attitude, and they are in general structure identical. The position of the head, eyes, and ears, the neck, the central vertebral column, the fore legs, which are arms in that position, the pelvis, the hind legs, all bear a close resemblance. Of course there are material differences; but they are evidently moulded upon one general plan. If there were a special creation for each species, why should they all necessarily have a kindred structure? ”

“ The characters, more or less common to all animals, man included, are next pointed out, when leave is taken of the invertebrates, and a consideration of the principal subdivisions of the group or sub-kingdom to which man belongs closes the chapter. The six succeeding chapters, or lessons, taking up in all 218 pages of the book, are upon the skeleton, wherein the various systems of bones are treated, each being described, first, as it is developed in man, and then as it appears in homologous parts of other vertebrates. ”

“ Hence they are all placed in a more inclusive division of animals, the class called mammals.
All mammals have the skeleton, or support of the body, on the inside, the axis of which is called the vertebral column. This feature also belongs to the classes of reptiles, amphibians, and fishes. It is therefore consistent to unite these classes by a general idea or conception into a great branch of animals called the vertebrates.
Returning from the general to the particular by successive steps, state the branch, class, order, family, genus, and species to which the cow belongs. ”

“ All the well-known, usually very clear proofs from palæontology, comparative anatomy, &c., which we are accustomed to meet with in evolutionist books are wanting here, the genealogical trees of the Equidæ, with the gradually diminishing number of toes and the varying teeth, of Planorbis multiformis, of the ammonites, the graduated series of stages exhibited by individual organs, for instance, from the ganglion merely sensitive to light up to the intricate eye, or from the rayed skeleton of the paired fins in fishes up to the five-fingered hands and feet of the higher vertebrates, &c. ”