. Elements of comparative anatomy. Anatomy, Comparative. Di COMPARATIVE ANATOMY, the products of which are developed in them in the same manner as are those of the free Medusae. 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 Medusas of a rela- tively high organisation, which only become sexually mature some time after leaving the Hydroid s
. Elements of comparative anatomy. Anatomy, Comparative. Di COMPARATIVE ANATOMY, the products of which are developed in them in the same manner as are those of the free Medusae. 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 Medusas of a rela- tively high organisation, which only become sexually mature some time after leaving the Hydroid stock, must be regarded as the widely-separateterminalpoints of one series. This phenomenon 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 medusiform buds and their modifications be considered to be,
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectanatomycomparative
