Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 EELATION OF METAMORPHOSIS TO FEETILITY. 121 on the contrary, which pass through a metamorphosis always arise from eggs of relatively small size, are hatched in an immature con- dition as larvae, and obtain independently, by their own activity, the materials which have been withheld from them while in the egg, but which are necessary for their full development. The number of embryos produced in the case of a direct development is, in pro
Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 EELATION OF METAMORPHOSIS TO FEETILITY. 121 on the contrary, which pass through a metamorphosis always arise from eggs of relatively small size, are hatched in an immature con- dition as larvae, and obtain independently, by their own activity, the materials which have been withheld from them while in the egg, but which are necessary for their full development. The number of embryos produced in the case of a direct development is, in proportion to the total weight of the material applied by the mother for reproductive purposes, far smaller than in the case of a develop- ment with metamorphosis. The fertility of animals whose young Fig. 112.—Later stages in the development of Pelobates fuscus. a, larva Tvithout limbs with well developed tail; b, older larva with hind limbs ; c, larva with two pairs of limbs; d, young frog with caudal stump j e, young frog after complete atrophy of tail. undergo a metamorphosis, or, in other words, the numl^er of ofTspring produced from a given mass of formative material, is increased to an extraordinary degree, and has, in the complicated relations of organic life, a great physiological significance, though systematically it is of little importance. Some time ago it was attempted to explain these indirect meta- morphoses, in which both processes of reduction and new development take place, as the result of the necessity which the simply organized
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