Origin of Species Variorum

Comparison with 1872

Text in this page (from paragraph 4920, sentence 500, word 25 to paragraph 4920, sentence 600, word 44) is not present in 1872

Now, if an insect, undergoing transformations like those of the Sitaris, were to become the progenitor of a whole new class of insects, the course of development of the new class would be widely different from that of our existing insects; and the first larval stage certainly would not represent the former condition of any adult and ancient form.

On the other hand it is highly probable that with many .. animals the embryonic or larval stages .. show us, more or less completely, the condition of the ... progenitor of the whole group in its adult state. In the great class of the Crustacea, forms wonderfully distinct from each other, namely, suctorial parasites, cirripedes, entomostraca, and even the malacostraca, appear at first as larvæ under the nauplius-form; and as these larvæ live and feed in the open sea, and are not adapted for any peculiar habits of life, and from other reasons assigned by Fritz Müller, it is probable that at some very remote period an independent adult animal, resembling the Nauplius, .. existed, and subsequently produced, ... along several divergent lines of descent, the .. above-named great Crustacean groups. So again it is probable, from what we know of the embryos of mammals, birds, fishes, and reptiles, that these animals are the modified descendants of some .. ancient progenitor, which was furnished in its adult state with branchiæ, .. a swim-bladder, four fin-like limbs, and a long tail, all fitted for an aquatic life.

devours it. It then undergoes a complete change; its eyes disappear; its legs and antennæ become rudimentary, and it feeds on honey; so that it now more closely resembles the ordinary larvæ of insects; ultimately it undergoes further transformations, and finally emerges as a perfect beetle. Now, if an insect, undergoing transformations like those of the Sitaris, had been the progenitor of the whole great class of insects, the general course of development, and especially that of the first larval stage, would probably have been widely different from what is actually the case; and it should be especially noted that the first larval stage would not have represented the adult condition of any insect.

On the other hand it is probable that with many groups of animals the earlier larval stages do show us, more or less completely, the form of the ancient and adult progenitor of the whole group. In the enormous class of the Crustacea, forms wonderfully distinct from each other, as the suctorial parasites, cirripedes, entomostraca, and even the malacostraca, appear in their first larval state under a similar nauplius form; and as these larvæ feed and live in the open sea, and are not adapted for any peculiar habits of life, and from other reasons assigned by Fritz Müller, it is probable that an independent adult animal, resembling the nauplius, formerly existed at a remote period, and has subsequently produced, through long-continued modification along several divergent lines of descent, the several above-named great Crustacean groups. So again it is probable, from what we know of the embryos of mammals, birds, fishes, and reptiles, that all the members in these four great classes are the modified descendants of some one ancient progenitor, which was furnished in its adult state with branchiæ, had a swim-bladder, four simple limbs, and a long tail fitted for an aquatic life.