Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote . elementarytextbo01clau Year: 1892-1893 126 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GKNEKAL. In the other cases in which the sexual and asexual forms mor- phologically resemble each other, as in Salpa, the origin of the alternation of generations may, as in the case of the origin of the dioacious from the hermaphrodite state, be traced back to the ten- dency towards the establishment of a division of labour acting upon an animal which possessed the capa
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote . elementarytextbo01clau Year: 1892-1893 126 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GKNEKAL. In the other cases in which the sexual and asexual forms mor- phologically resemble each other, as in Salpa, the origin of the alternation of generations may, as in the case of the origin of the dioacious from the hermaphrodite state, be traced back to the ten- dency towards the establishment of a division of labour acting upon an animal which possessed the capacity of sexual and asexual repro- duction. It was advantageous for the formation of the regular chain of buds (stolo prolifer) that the power of sexual reproduction should be suppressed, and that the %%%%%%%% generative organs should be- come rudimentary and finally vanish in the budding indivi- dual >; while, on the other hand, in the individuals united in the chain, the gene- rative organs were early de- veloped, and the stolo prolifer was aborted and completely vanished. Special forms of alternation of generations may be di>- tinguished in which colonies are formed as the result of the asexual reproduction by budding from a single animal, the buds remaining attached and developing into individuals which differ considerably in structure and appearance, and each of which performs special functions in maintaining the FIG. 113.—g, Fully developed Strobila with sepa- colony (nutritive, protective, sexual, etc.) Such a form of • v, rating Ephyrae. h, Free ;hyra (of about 1 '5 to 2 mm. diameter. alternation of generations is known as }>oIi/>/torpJtism,* and reaches a great complication in the polymorphous colonies of the Siphonophora. A form of reproduction which closely resembles metagenesis, but which genetically has quite a different explanation, is the lately * K. Leuckart, ' Ueber den Polymorphismus der Indivuluen oder Erscheinung der Arbcitstheilung i
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