Page:The New International Encyclopædia 1st ed. v. 13.djvu/408

* METAMORPHOSIS. 372 METAMORPHOSIS. stages they lead different lives and are subjected to different environments, the huvie for the most part being frecswininiinfr and living near the surface of the water, vhih> the parents arc sta- tionary. The result of this change of haliits and form undoubtedly is to prevent the extinction of the species, since if at a given moment tlie par- ents were swept out of existence, the young, living under very different circumstances, would sur- vive, deveh)]), and represent the species. Again in the marine species of worms, Crustacea, etc. .the free-swinnning young (larva") are borne about by oceanic and tidal currents, and in this way what in adult life are the most scdenlary forms be- cotue widely distributed from one part of the world to another. On the other hand, the larval forms of fixed marine animals serve as food for fishes, especially young fishes, and numerous invertebrates. Thus were it not for the meta- morphoses of animals, many species would be- come extinct sooner than they do, while the great overplus of larval forms gives to many other spe- cies of animals a secure hold on existence. As an example of metamorphosis we may cite that of a butterlly. lly. (U' bee. Their life is di- vided into four stages, the embryo passed within the egg, the larva. puj)a or chrysalis, and imago. An insect after hatching lives, so to speak, three different lives, having distinct bodily struc- tures and existing under very different conditions as regards food, enemies, etc. The caterpillar, for example, has big jaws, which in the winged or adult state are entirely want- ing. Other radical changes are observable in the body and a])])endages, and also in the inter- nal organs. The term 'larva' (q.v.), as applied to the first stage of animals, is a very variable and indefinite one, that of insects in general be- ing a much more higlily organized animal than the larva of a worm, starfish, or crustacean. Wing- less insects (synaptera) do not pass through a metamorphosis. That of winged insects is said to be "incomplete' or 'complete.' An example of incom- plete metamorphosis is that of locusts and grass- ho])pcrs. In these insects the freshly hatched young differs from the adult only in being with- out wings. The different stages of metamor- phosis are not primitive, inherited from some early form, but arc acquired characters; the nau- plius stage of most Crustacea, and the caterpillar, maggot, or grub of insects, are forms which were adaptations to changed modes of life, inducing use or disuse of certain organs. At first insects were ametabolous. and it was not until perhaps the middle of the Paleozoic era that insects with a metamorphosis began to exist. IlYPERMPrAMOHi'iin.sis. A condition in insects wherein they pass through more than the three normal stages. The best known examples are the supernumerary stages of ^[eloe. Stylops. etc. In the oil-beetle (Meloi-) the freshly hatched young is an active, minute campiidia-like larva, which inhaluts the nests of wilil bees, feeding upon the eggs of Iheir hosts. This .sedentary mode of life reacts upon the organism, and after molting in the second larval stage it is grub like, the body thick, soft and fleshy (carabidoid stage), and it feeds on honey. At the next molt the insect is motionless and nearly footles.s (semipupal stage). It then changes to a third larval form, wlien it resembles the maggot or lnrv,a of a bee. It then transforms into a genuine pupa, and finally into the beetle. It will be seen that at nearlv each stage its mode of life, kind of food, etc., cliange. Slppbessed Metamorphosis. This phenome- non, or "direct development,' is a curtailment or absolute loss of primitive larval characters, or a forcing back of larval features or structures, until they are either passed through in the embryo be- fore hatching or entirely lost, due to the lapse of heredity. Thus in all the insects with a meta- morphosis there exists what is called "polypody' in the embryo, except in the Diptera. where "it has been known to exist only in one case. The embryos of other metabolous insects than flies at a certain period have abdominal legs, showing their descent from a Peripatus or myriapodous ancestry. The eam]iodeoid characters of the larva of Coleoptera also become suppressed and lost in the more specialized moths, bees (Hymenoptera), and Diptera. This is ex]dained by their being crowded out, due to the acquisition of later ac- quired characters better adapted to their changed, new mode of life. This abbreviated metamorphosis is seen also in the Crustacea, as the lobster (q.v.), and more cs]iceially in certain shrimps and crabs, which, owing to changed conditions, hatch in the adult form, passing through the nauplius and zo8a stages in the embryo. It is also seen in the frogs (q.v.), where the different degrees of metamor- phosis are plainly due to great dift'erenccs in the conditions of life. See Nidificatiox. Causes of Metamoupiiosis. These are obscure, but it is plain that the different stages are ex- aggerated or proiKiunccd ])cri(icls in tlie growth of the animal, and that the fundamental causes are the same as those which have initiated and controlled the origin of species. This is plainly seen in aquatic larvtc, the young of forms whose larva; were originally terrestrial. The mmiber- less contrivances and temporary larval organs, especially seen in dipterous larva", are evidently adaptations to the needs of the insect during its temporary aquatic life, these being cast aside when the animals jiass to .a different medium. Bim.iOGRAPiiY. Weismann. '"Die naehenibry- onale Entwicklung der JInseidcn." in Zcitschrift fiir ■ic-ifisenscluiftliche Znolofiic, vol. xiv. ( 1864) ; Korschelt and Heider. Trxl-hook of the Einbry- oloqy of Jnvcrlchratc.i (London. 1895-1000) : Lub- bock. The Mctnmnriiltoscs of hmcctsi (ib., 1874); Packard, Text-hook of Entomologti (New York, 1808). METAMORPHOSIS (in plants). Goethe's doctrine which seeks to account for the observed connection between the dilVerent organs of a leafy nature in (he same plant, and chielly developed and applied to what may be called foliar organs. The stem came into consideration only as carry- ing leaves, and the root was almost entirely disre- garded. The theory assumes for foliar structures an ideal fundamental organ, from which different leaf forms could be derived. In its applica- tion this ideal form came to niean (o nioxt botanists an ordinary foliage leaf, and foliar structures have been in the main presented from this standpoint. l'"or exnni])le. the parts of the flower are commonly spoken of as modified or metamorphosed leaves; and when petals or sta- mens are abnormally replaced by foliage-like structures they are said to revert to the primi- tive condition and to prove derivation from leaves by modification. ]forpholog^" long ago disproved this iilealistic metamorphosis, and it does not re-