Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 94 co:mpaeative anatomy. the products of wliich are developed in tliem in tlie same manner as are those of the free Medusfe. With these are connected still simpler forms of buds^ and the series ends with buds the structure of which has scarcely anything in common with a Medusa. But the series which leads to these is perfect, owing to numerous intermediate forms, so that external buds, merely containing generative products, and Medusee of a rela- tively high organisation, which only become
Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 94 co:mpaeative anatomy. the products of wliich are developed in tliem in tlie same manner as are those of the free Medusfe. With these are connected still simpler forms of buds^ and the series ends with buds the structure of which has scarcely anything in common with a Medusa. But the series which leads to these is perfect, owing to numerous intermediate forms, so that external buds, merely containing generative products, and Medusee of a rela- tively high organisation, which only become sexually mature some time after leaving the Hydroid stock, must be regarded as the widely-separate terminalpoints of one series. This phaenomenon is ex- plained by the conception of a division of labour, in which the function of feeding the stock falls to the share of the individuals which remain ses- sile, while others which are broken off take on the duty of sexual reproduction. Those buds which will become free have a higher organisation, which has been gradually de- veloped from the lower forms, and primitively resembled those that remain sessile. The separation from the stock may therefore be regarded as the primary cause of the differen- tiation of the sexual individuals in the medusoid direction, while the permanence of the sessile habit of the medusoid buds, in other cases, is accom- panied by a degeneration of their medusoid organisation. But if this organisation, as we supposed above, has been obtained by a primitive freedom of life, the medusoid buds must necessarily be regarded not as arrested in an onward development, but rather as Medusa-buds in course of degeneration. A definite conclusion on the subject is not possible, on account of the fact that the several stages of degeneration might be precisely similar to those of deve- lopment, and retrogressive metamorphoses have not been directly observed. The gemmation of generative individuals, for such must the medus
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