. Bulletin - United States National Museum. Science. Figs. 4 AND 5.—DOKSAL AND VENTRAL VIEWS OF THEORETIC TYPEMBRYO OF StELLEROIDEA. Ax, VEN- TRAL OR MARGINAL AXILLARIES OR BASAL INFRAMARGINALS; CD, CENTRO-DORSAL; R, PRIMORDIAL EADLALS; Sml, DORSAL INTERRADIALS OR PRIMORDIAL SUPRAMARGINALS. smooth, and loosely adjoining. Tracing them down the columns, the specific characters are seen to develop and finally the basal pieces are found to be the most modified of all. This is particularly true of the dorsal columns where the most ornate plates are the oldest. In the different species of Hudsonaste
. Bulletin - United States National Museum. Science. Figs. 4 AND 5.—DOKSAL AND VENTRAL VIEWS OF THEORETIC TYPEMBRYO OF StELLEROIDEA. Ax, VEN- TRAL OR MARGINAL AXILLARIES OR BASAL INFRAMARGINALS; CD, CENTRO-DORSAL; R, PRIMORDIAL EADLALS; Sml, DORSAL INTERRADIALS OR PRIMORDIAL SUPRAMARGINALS. smooth, and loosely adjoining. Tracing them down the columns, the specific characters are seen to develop and finally the basal pieces are found to be the most modified of all. This is particularly true of the dorsal columns where the most ornate plates are the oldest. In the different species of Hudsonaster one can also trace the changes chronogenetically, as for instance in the basal radialia and supra- marginaUa. In the oldest species these plates are not at all, or but very slightly stellate, more so in H. incomptus, and most so in the youngest and largest species, 77. rugosus. In the stocks with more complex skeletons, the ontogenetic varia- tions in the plates can be traced in the same way. However, as these forms almost always have more or less of accessory plates that are introduced nearly throughout the entire skeleton during the juvenile growth and even at maturity, the study is complicated by the inter- mixture of ossicles of varying age. 1 See Jackson, Phylogeny of the Ecliiiu, Mem. Boston Soc. Nat. Hist., vol. 7, 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 United States National Museum; Smithsonian Institution; United States. Dept. of the Interior. Washington : Smithsonian Institution Press, [etc. ]; for sale by the Supt. of Docs. , U. S. Govt Print. Off.
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