Page:Insects - Their Ways and Means of Living.djvu/284



it would be greatly handicapped for living its own lire, and this would be quite as detrimental to the adult, which must be developed from the young. Therefore, nature bas devised a scheme for separating the young from the adult, by which the latter is allowed to take full advan- tage of its wings without imposing a hardship or a dis- ability on its flightless offspring. The device sets aside the ordinary workings of heredity and makes it possible for a structural modification to be developed in the adult and to be suppressed in the young until the time of change from the last immature stage to that of the adult. Thus we may state as a second principle of metamor- phosis that an addt insect ma develop str«tural characters adaptive to habits that depend'on the power of flight, which are suppressed in the young, where they would be detrimental br. reason of the lack of wings. When parents, now, assert their independence, what can we expect of the offspring? Certainly only a similar declaration of rights. A young insect, once freed from any obligation to follow in the anatomical footsteps of its progenitors, so long as it finally reverts to the form of the latter, soon adopts habits of its own; and then acquires a form, physical characters, and instincts adapted to such habits. Thus, the young dragonfly (Fig. 34) bas de- parted from the path of its ancestors; it bas adopted a lire in the water, where it feeds upon living creatures which it pursues by its perfection in the art of swimming and cap- tures by a special grasping organ developed from the under li (B). Lire in the water, too, entails an adaptation for aquatic respiration. AIl the special acquisitions in the structure of the young insect, however, must be dis- carded at the rime of its change to the adult. A third principle, then, which follows somewhat as a corollary from the second, shows us that the young of insects may adopt habits advantageous to themselves, and take on adoptive structt«res that have no regard to the form of the adult «md that are discarded at tke fiml transformation.

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