. Text-book of embryology. Embryology. XVI ECHINODEEMATA 54c sacs, whilst that of Auricularia is filled with mesenchyme. The mode of segmentation of the coelom is widely different in Auricularia from what it is in Bipinnaria. On the other hand, the retention of the larval mouth and its shift towards the left, as seen in Holo- thuroidea, is not found in Asteroidea or Echinoidea, and is paralleled only by the development of the Ophiuroidea. The growth of the buccal tentacles into the atrium, the larval stomodaeum, recalls what occurs in Ophiuroidea and in Echinoidea, if our conception of th
. Text-book of embryology. Embryology. XVI ECHINODEEMATA 54c sacs, whilst that of Auricularia is filled with mesenchyme. The mode of segmentation of the coelom is widely different in Auricularia from what it is in Bipinnaria. On the other hand, the retention of the larval mouth and its shift towards the left, as seen in Holo- thuroidea, is not found in Asteroidea or Echinoidea, and is paralleled only by the development of the Ophiuroidea. The growth of the buccal tentacles into the atrium, the larval stomodaeum, recalls what occurs in Ophiuroidea and in Echinoidea, if our conception of the amniotic space of the latter as a separated. ca/c Fig. 402. Post-larval stage in the development of Cuomnaria saxicola viewed from the side. (Original.) 6.(, buccal tentacles ; (./, paired tube feet; v, valves into which the atrium splits. portion of the stomodaeum be admitted; but there is an important difference, for the primary tentacles of Asteroidea, Ophiuroidea, and Echinoidea are the tips of the radial canals, lut the tips of the radial canals of Holothuroidea do not protrude into the atrium, only their basal branches, the buccal tentacles, do so. More light on this interest- ing difference will be obtained when the complete history of Gucumaria saxicola is worked out. This species, which is very closely allied to Gucumaria planci, has been reared through the metamorphosis by the authorities of the Plymouth Biological Station. The adult anatomy of a Holothuroid suggests the view that the group may have been derived from early Echinoidea in which the test. 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 MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
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