The royal natural history . SWELLINGS IN THE PINNULES OF CRINOIDS PRODUCED BY A parasite (twice nat. size). The Blastoids,—Class Blastoidea. The Blastoidea constitute a compact group, pretty clearly marked off fromboth Cystidea and Crinoidea, which they resemble in the upward position of themouth and the generally fixed habit. The chief character that separates blastoidsfrom other echinoderms is the presence of an elongate plate, the lancet-plate,underlying the ambulacrum and pierced by a canal supposed to have contained theradial water-vessel. These five canals meet in a circular canal round
The royal natural history . SWELLINGS IN THE PINNULES OF CRINOIDS PRODUCED BY A parasite (twice nat. size). The Blastoids,—Class Blastoidea. The Blastoidea constitute a compact group, pretty clearly marked off fromboth Cystidea and Crinoidea, which they resemble in the upward position of themouth and the generally fixed habit. The chief character that separates blastoidsfrom other echinoderms is the presence of an elongate plate, the lancet-plate,underlying the ambulacrum and pierced by a canal supposed to have contained theradial water-vessel. These five canals meet in a circular canal round the mouth,but there is no evidence that they were connected with tube-feet as in otherechinoderms. Each side of each ambulacrum was lined by a row of delicate,unbranched arms; and the food-grooves of these arms passed to a single grooverunning down the middle of the surface of the ambulacrum, and these five groovesthen passed up to the mouth. The most interesting structures in the Blastoidea are the hydrospires. In sucha
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
