CHANGE OF FUNCTION. During the metamorphosis of insects, Crustacea, and other animals, organs at first adapted for certain uses become, with change of conditions of life, media, and consequently of habits, adapted to quite dif ferent uses or functions. Thus in the young larva (Nauplius) of many of the lower Crus tacea, the three pairs of head appendages are formed for swimming; the first two pairs after ward change into the two pairs of antenna, the third pair becoming the jaws of the adult. In the tadpole, which lives on dead leaves or animal matter, the intestine is very long and coiled, but in after life, when the frog feeds on living insects, it is very much changed in form, being much shorter. These are examples of an ontogenetic change of function. There are many examples of change of function by sup pression of the original or chief function, what was a minor use becoming the chief one. Examples of a phylogenetic change of function are the transformation of the jaws of biting insects into the needle-like elements, aiding in the formation of the beak of bugs (q.v.); the transformation of the hypopharynx of caddis flies into the piercing organ of fleas and flies; the modification of the maxilla of biting insects into the spiral tongue of the butterfly. The
mouth-parts of bees and butterflies lost their primitive functions and adopted entirely new shapes and uses after flowers appeared. Among fishes the clearest example is the change of the swimming-bladder of the gar pike, where it also functions as a breathing organ, until in the lung-fishes, which have probably descended from some ganoid, it becomes a lung.
These changes of functions are due to change of the surroundings, and consequently of habits, finally bringing about change of func tion. Hertwig states that a muscle may from many causes become functionless, but finally becomes transformed into a ligamentous band. What are the gill-supports of fishes may, as the results in certain of their descendants of the adoption of a terrestrial mode of life, be come in part degenerate, while another part persists by assuming a new function, forming thejaws, the hyoid bone and the small bones of the car, which are morphologically the same structures as the gill-arches. Consult Dohm, 'Der Ursprung der Wirbelthicre and das Prin zip des Funktionwechsels' ; Hertwig-Kingsley, 'Manual of Zoology.'