A treatise on zoology . )icalsystems arose independently in ditlerentlines of descent. If, however, it be im-|)()ssil)le to regard the apical systems ofKchinoidoa and Stelleroidea as homogenetic with that of Crinoidea,there can bo no objection to the statement that similar plates aredeveloped in a similar position with regard to the fundamentalanatomy, under the intluence of somewhat similar causes. The Asteroids were probably the last groiip to branch oil fromthe fixed FichinfxhMnia. Ihuice it is that they retain many features. Via. xn. Dorsal, /.»?. uhnral, vinw ofAstfrina gilihnstt, tMti da
A treatise on zoology . )icalsystems arose independently in ditlerentlines of descent. If, however, it be im-|)()ssil)le to regard the apical systems ofKchinoidoa and Stelleroidea as homogenetic with that of Crinoidea,there can bo no objection to the statement that similar plates aredeveloped in a similar position with regard to the fundamentalanatomy, under the intluence of somewhat similar causes. The Asteroids were probably the last groiip to branch oil fromthe fixed FichinfxhMnia. Ihuice it is that they retain many features. Via. xn. Dorsal, /.»?. uhnral, vinw ofAstfrina gilihnstt, tMti days olil(aftorLiuiwi^j). MhovvM pn-Driilloll* (/.) in)w oil oriil Midf ;rinliiiitMits of tl vi- uriiis innrknil\>y tlvt) trriiiliinl |)(7); al-turiiafinv; witli tlust- arc llvfImMftlM (/•); RM*I lit Im ;alWi<l i|oim)-c»Mitral ; M,in«di«j»orit«. xi»<. ECHINODERMA—GENERAL DESCRIPTION 15 of the Pentadcea^ together with epithelial nerves on the floor ofthe arm-grooves, as in Pelmatozoa. The Ophiuroids are, asexplained under Stelleroidea, scarcely to be distinguished fromAsteroids. Whether they branched ofl at an earlier date or no isuncertain ; at any rate, they have progressed farther from thePciitactaa type, in so far as the radial nerves have sunk belowthe surface and are covered by epineural canals, which probablyrepresent closed food-grooves (Fig. XIII. 1 and 2).
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
