Below the twelve models in Case 36 may be seen a representation of three stages in the history of the Feather-star (_Antedon bifida_). The larvæ of this Echinoderm are not free, but are attached by a stalk (Fig. 6); in the common Feather-star and other _Comatulidæ_ the stalk is found during larval stages only; in others, such as _Pentacrinus_, it persists throughout life. The presence or absence of this stalk has been taken as the first character of importance in the classification of Echinoderma which may be divided into two groups:— A. PELMATOZOA,[24] or Echinoderms provided with a stalk throughout life or in the larval stages only. To this group belong the _Crinoidea_, and the extinct _Blastoidea_, and _Cystidea_. [Illustration: Fig. 6. Pentacrinoid stage of _Antedon rosacea_. _a_, arms; _b_, basals; _r_, radials; _s_, stalk. ] B. ECHINOZOA, or Echinoderms without stalks at any time of their existence. To this group belong the _Asteroidea_, _Ophiuroidea_, _Echinoidea_, and _Holothurioidea_. CRINOIDEA.—This Order may be described as stalked, globular, or cup-shaped Echinoderms, in which the oral surface of the calyx or disk looks upwards, and in which five jointed and generally branched rays arise from the central disk. Their joints have jointed pinnules at their sides, and the sucking-feet have the form of tentacles. The stalked representatives of this Order are placed on tables and brackets near the south door, and are worthy of being particularly noticed for their fine preservation, size, and beauty. The largest specimen of _Pentacrinus decorus_ was taken on a telegraph-wire, to the covering of which the stalk of the Crinoid is still attached. _Metacrinus_ is a more lately discovered genus, which appears to be confined to the eastern seas. A few dried unstalked Crinoids are shown in Table-case 1; these show the leading modifications of structure in the two great genera _Antedon_ and _Actinometra_. [Illustration: Fig. 7. Comet form of _Linckia_. ] ASTEROIDEA.—This Order comprises Echinoderms with a depressed body of pentagonal or star-like shape, to the ventral surface of which the ambulacral feet are confined. The rays are more or less elongate movable arms, with skeletal structures, which consist of transversely arranged, paired, calcareous plates, articulated with each other like vertebræ, the series extending from the mouth to the end of the arms. The groove in which the ambulacral feet are arranged is uncovered. Typical specimens of this Order are exhibited in Cases 2 & 3, in which the great variety of form in the genus _Asterias_ and beautiful examples of _Acanthaster_ are shown. Cases 6 & 7 contain specimens illustrating the curious habit of self-mutilation possessed by so many Echinoderms; among Starfishes, and notably in the genus _Linckia_, the single arms separated from the disk are able to develop a fresh disk and arms, and so to multiply the species. Cases 9–11 contain fine series of _Oreaster_.