Page - 488 - in The Origin of Species

488 ORIGIN" OF SPECIES Afterwards they undergo a complete change; their eyes dis- appear ; their legs and antennae become rudimentar\-, and they feed on honey; so that they now more closely resemble the ordinary larvae of insects; ultimately they undergo a further transformation, and finally emerge as the perfect beetle. 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 exist- ing 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 embr\'onic 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 malacos- traca, appear at first as larvse under the nauplius-form; and as these larvae live and feed in the open sea, and are not adapted for any peculiar habits of life, and from other reasons assigned by Fritz Miiller, it is probable that at some very remote period an independent adult animal, resembling the Xauplius, existed, and subsequently produced, along sev- eral divergent lines of descent, the above-named great Crus- tacean 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 branchiae, a swim-bladder, four fin-like limbs, and a long tail, all fitted for an aquatic life. As all the organic beings, extinct and recent, which have ever lived, can be arranged within a few great classes; and as all within each class have, according to our theory, been connected together by fine gradations, the best, and, if our collections were nearly perfect, the only possible arrange- ment, would be genealogical; descent being the hidden bond of connexion which naturalists have been seeking under the term of the Natural System. On this view we can under- stand how it is that, in the eves of most naturalists, the