The polychaeteSpintherand the origin of the Arthropoda

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Abstract
(1)The differences between small and large specimens of Spinther arcticus Sars show how the great width and the approximation to radial symmetry, in the adult is secondarily developed from young worms of more normal polychaete proportions. (2)The anatomy of Spinther arcticus Sars is described and related to function and habits. (3)The biramous parapodium of Spinther is not a lobopodium, and provides no evidence for supposing that annelids arose from lobopodial worms, or that the lobopod ancestors of arthropods arose from organisms of the Spinther type. (4)The proboscis of Spinther is unique among polychaetes, but is protruded by the normal polychaete method. Spinther provides no evidence in favour of the reality of the Proboscifera. (5)The structure and mode of action of the onychophoran lobopodium is described and shown to be entirely unlike the parapodium in these respects and to be easily referable to a jointed leg. (6)Spinther provides no evidence in favour of Sharov's views on the origin and evolution of the Arthropoda.

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