Origin of Species Variorum

Comparison with 1866

may be used literally; and the wonderful fact of the jaws, for instance, of a crab retaining numerous characters, which they probably would have retained through inheritance, if they had really been metamorphosed during a long course of descent from true though simple legs, is explained.

Embryology and Development .

This is one of the most important departments of natural history. Herein are included the ordinary metamorphoses of insects, with which every one is familiar. These are generally effected somewhat abruptly by a few stages and in a concealed manner; but the transformations are in reality numerous and graduated. For instance, Sir J. Lubbock has recently shown that a certain ephemerous insect (Chlöeon) during its development moults above twenty times, and each time undergoes a certain amount of change; in such cases we probably behold the act of metamorphosis in its natural or primary progress. ↑ What great changes of structure are effected during the development of some animals is seen in the case of insects, but still more plainly with many crustaceans. When, however, we read of the several wonderful cases, recently discovered, of the so-called alternate generations of animals, we come to the climax of developmental transformation. What fact can be more astonishing than that a delicate branching coralline, studded with polypi and attached to a submarine rock, should produce, first by budding and then by transverse division, a host of huge floating jelly-fishes; and that these should produce eggs, from which are hatched swimming animalcules, which attach themselves to rocks and become developed into branching corallines; and so on in an endless cycle? Hence it will be seen that I follow those naturalists who look at all cases of alternate generation, as essentially modifications of the process of budding, which may supervene at any stage of development. This view of the close connection between alternate generations and ordinary metamorphoses has recently been much strengthened by Wagner's discovery of the larva of a Cecidomyia,— that is of the maggot of a fly, — producing asexually within its body other and similar larvæ; these again repeating the process. ↑ ↑

It has already been remarked that various parts and organs of the same individual animal are during an early embryonic period exactly like each other, but become in the adult state widely different and serve for widely different purposes. So again it has already been remarked that the embryos of distinct species and genera within the same class are generally closely similar, but become when fully developed widely dissimilar. A better proof of this latter fact cannot be given than that by Von Baer, namely, that "the embryos of mammalia, of birds, lizards, and snakes, probably also of chelonia, are in their earliest states exceedingly like one another, both as a whole and in the mode of development of their parts; so much so, in fact, that we can often distinguish the embryos only by their size. ↑ In my possession are two little embryos in spirit, whose names I have omitted to attach, and at present I am quite unable to say to what class they belong. They may be lizards or small birds, or very young mammalia, so complete is the similarity in the mode of formation of the head and trunk in these animals. The extremities, however, are still absent in these embryos. But even if they had existed in the earliest stage of their development we should learn nothing, for the feet of lizards and mammals, the wings and feet of birds, no less than the hands and feet of man, all arise from the same fundamental form." The vermiform larvæ of moths, flies, beetles, &, generally resemble each other much more closely than do the mature insects; but in the case of larvæ, the embryos are active, and from having been adapted for special lines of life sometimes differ much from each other. A trace of the law of embryonic resemblance, occasionally lasts till a rather late age: thus birds of the same genus, and of closely allied genera, often resemble each other in their first and second plumage; as we see in the spotted feathers in the thrush group. In the cat tribe, most of the species are striped or spotted in lines; and stripes or spots can be plainly distinguished in the whelp of the lion and the puma. We occasionally though rarely see something of this kind in plants: thus the first leaves of the ulex or furze, and the first leaves of the phyllodineous acacias, are pinnate or divided like the ordinary leaves of the leguminosæ.

The points of structure, in which the embryos of widely different animals of the same class resemble each other, often have no direct relation to their conditions

may be used literally; and the wonderful fact of the jaws, for instance, of a crab retaining numerous characters, which they would probably have retained through inheritance, if they had really been metamorphosed during a long course of descent from true legs, or from some simple appendage, is explained. ↑ ↑

Embryology .—

It has already been casually remarked that certain organs in the individual, which when mature become widely different and serve for different purposes, are in the embryo exactly alike. The embryos, also, of distinct animals within the same class are often strikingly similar: a better proof of this cannot be given, than a circumstance mentioned by Agassiz, namely, that having forgotten to ticket the embryo of some vertebrate animal, he cannot now tell whether it be that of a mammal, bird, or reptile. The vermiform larvæ of moths, flies, beetles, &c., resemble each other much more closely than do the mature insects; but in the case of larvæ, the embryos are active, and have been adapted for special lines of life. A trace of the law of embryonic resemblance, sometimes lasts till a rather late age: thus birds of the same genus, and of closely allied genera, often resemble each other in their first and second plumage; as we see in the spotted feathers in the thrush group. In the cat tribe, most of the species are striped or spotted in lines; and stripes can be plainly distinguished in the whelp of the lion. We occasionally though rarely see something of this kind in plants: thus the embryonic leaves of the ulex or furze, and the first leaves of the phyllodineous acaceas, are pinnate or divided like the ordinary leaves of the leguminosæ.

The points of structure, in which the embryos of widely different animals of the same class resemble each other, often have no direct relation to their condi- tions