. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. 262 ELEMENTS OF BIOLOGY Metagenesis in Other Metazoa. A true alternation of sexual and asexual generations is found in various other Metazoa; certain parasitic Nemathelminthes, some of the Platyhelminthes, and in some lower chordates. Metagenesis also occurs in some insects. In some ichneumon flies, a type of insect related to bees, wasps, and ants, the eggs of the female are laid in the larvae of other insects. In some species a single egg in the process of development gives rise to a great
. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. 262 ELEMENTS OF BIOLOGY Metagenesis in Other Metazoa. A true alternation of sexual and asexual generations is found in various other Metazoa; certain parasitic Nemathelminthes, some of the Platyhelminthes, and in some lower chordates. Metagenesis also occurs in some insects. In some ichneumon flies, a type of insect related to bees, wasps, and ants, the eggs of the female are laid in the larvae of other insects. In some species a single egg in the process of development gives rise to a great number, several hundred, larval parasites in the body of G£PM OF 13 INDIVIDUALS EGG WALL. NUTRITIVE ORGAN Fig. 177.—Polyembryony in the development of an insect, Platygaster vernaUs, order Hymenoptera, parasitic in the eggs and larvx of the Hessian fly. Sixteen new individuals may hatch from a single fertilized egg; thirteen are shown as early germs in the figure. (After Patterson, after Leiby and Hill.) the host larva. There occurs here by multiple divisions of the germ, an agamic reproduction of the developing parasite, a phenomenon known as polyembryony (Fig. 177). Essentially it is a process o£ metagenesis, for a sexual process of reproduction is followed by an asexual fragmentation of the embryo of the new generation. Sufficient has been said here to emphasize the fact that alternation of sexual and asexual generations is a very common type of life | cycle in both plants and animals. Plants have developed this type of reproductive phenomenon as a major feature of the highest and 1 most complicated plants; animals have continued the sexual type - of reproduction as the method in the most highly developed Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Buchanan, James William, 1888-. New York
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