Seite - 478 - in The Origin of Species

478 ORIGIN OF SPECIES DEVELOPMENT AND EMBRYOLOGY This is one of the most important subjects in the whole round of natural history. The metamorphoses of insects, with which every one is familiar, are generally effected ab- ruptly by a few stages ; but the transformations are in reality immerous and gradual, though concealed. A certain ephem- erous insect (Chloeon) during its development, moults, as shown by Sir J. Lubbock, above twenty times, and each time undergoes a certain amount of change; and in this case we see the act of metamorphosis performed in a pri- mary and gradual manner. Many insects, and especially cer- tain crustaceans, show us what wonderful changes of struc- ture can be effected during development. Such changes, however, reach their acme in the so-called alternate genera- tions of some of the lower animals. It is, for instance, an astonishing fact that a delicate branching coralline, studded with polypi and attached to a submarine rock, should pro- duce, first by budding and then by transverse division, a host of huge floating jelly-fishes; and that these should pro- duce 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. The belief in the essential identity of the process of alternate generation and of ordinary metamorphosis has been greatly strengthened by Wagner's discovery of the larva or maggot of £ fly, namely the Cecidomyia, producing asexually other larvae, and these others, which finally are developed into mature males and females, propagating their kind in the ordinary manner by eggs. It may be worth notice that when Wagner's remarkable discovery was first announced, I was asked how was it possible to account for the larvae of this fly having acquired the power of asexual reproduction. As long as the case remained unique no answer could be given. But already Grimm has shown that another fly, a Chironomus, reproduces itself in nearly the same manner, and he believes that this occurs frequently m the Order. It is the pupa, and not the larva, of the Chironomus which has this power; and Grimm further shows that this case, to a certain extent, "unites that