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 ECHINODERMATA 619 the foot of a wine-glass (Fig. 2). In some crinoids which have no ancestral form than was furnished by any calyculate echinoderm, trace of a stem {e.g., Marsupites) a pentagonal plate is found at and by the Sarasins, who derived the echinoids from the holothe bottom of the cup, where the stem thurians through forms with flexible tests (Echinothuridae, which, would naturally have arisen (“centrale” however, are now known to be specialized in this respect). The in Fig. 1) ; and since it was believed support that appeared to be given to the theory by the presence of that the stem always grew by addition supposed calycinal plates in the embryo of echinoids and asteroids of ossicles immediately below the infrahas been, in the opinion of many, undermined by MacBride (op. cit.), basals, it was inferred that this penwho has insisted that in the fixed stage of the developing starfish, tagonal plate was the centro-dorsal in r.p'c Asterina, the relations of these plates to the stem are quite different its primitive position, as though the to those which they bear in the developing and adult crinoid. wine - glass had been evolved from a But, however correct the observations and the homologies of tumbler by pulling the bottom out to MacBride may be, they do not, as Bury (op. cit.) has well pointed form the foot. The oro-eentral was, it out, afford sufficient grounds for his inference that the abactinal must be admitted, a theoretical concep(i.e., aboral) poles of starfish and crinoids are not comparable with tion due to a desire for symmetry, and one another, and that all conclusions based on the supposed was not confirmed by anything better homology of the dorso-central of echinoids and asteroids with that than some erroneous observations on Fl - 2 An ear of crinoids are incorrect. Bury himself, however, has inflicted a certain fossils, which were supposed to dj evelo -~ ment ly fstage in the severe blow on the theory by his proof that the so-called oculars of show a plate at the oral pole between the showing, P the foot-plate ? Araedxm, or which were supposed to represent the radials, are five orals ; but this plate, so far as it exists “ dorso-central ” fp at the Echmoidea, homologous with the “terminals” (i.e., the plates at the tips of end of the stem col. Some at all, is now known to be nothing but of the thecal plates, infra- the rays) in Asteroidea and Ophiuroidea, and therefore not homoan oral shifted in position. The theory basals IB, basals B, and logous with the radially disposed plates often seen around the was that all the plates just described, orals 0v aic are forming arounu around aboial pole of those animals. For, if these radial constituents of and more particularly those of the cup, the body-cavities r.pc and the supposed apical system in an ophiurid have really some other p which were termed “the calycinal sysfj1.6 water-pore, ongm, why can we not say the same of the supposed basals? tern,” could be traced, not merely in all ^ XS3 Indeed, Bury is constrained to admit that the view of Semon and crinoids, but in all Echinoderms, whether otheis may be correct, and that these so-called calycinal systems fixed forms such as cystids and blastoids, or free forms such as may not be heirlooms from a calyculate ancestor, but may have ophiuroids and echinoids, even—with the eye of faith in holo- been independently developed in the various classes owing to the thurians. It was admitted that these elements might atrophy, action of similar causes. That this view must be correct is urged or be displaced, or be otherwise obscured ; but their complete and t,aden ts of fossils - isPalaeontology lends no support symmetrical disposition was regarded as ty ] leal and original. ifT 1 that* the dorso-central a primitive element; it exists tointhe noneidea of Thus the genera exhibiting it were regarded as primitive^ and the early echinoids, but its origin from the minor plates around those orders and classes in which it was least obscured were sup- the amis is seen in the Saleniidse. There is no reason to suppose posed to approach most nearly the ancestral Echinoderm. Every- that the central apical plate of certain free-swimming crinoids has one knows that an “apical system,” composed of two circlets any more to do with the distal foot-plate of the larval Antedon known as “genitals” or basals and “oculars” or radials, occurs stem than has the so-called centro-dorsal of Antedon itself, which round the aboral pole of echinoids (Fig. 3, A), and that a few is nothing but the compressed proximal end of the stem. ’ As for the supposed basals of Echinoidea, Asteroidea, and Ophiuroidea, they are scarcely to be distinguished among the ten or more small plates that surround the anus of Bothriocidaris, which is the oldest and probably the most ancestral of fossil sea-urchins (Fig. 5) A calycinal system may be quite apparent in the later Ophiuroidea and m a few Asteroidea, but there is no trace of it in the older Palaeozoic types, unless we are to transfer the appellation to the terminals. Those plates are perhaps constant throughout seaurchins and starfish (though it would puzzle any one to detect them in certain Silurian echinoids), and they may be traced in some of the fixed echinoderms ; but there is no proof that they lepresent the radials of a simple crinoid, and there are certainly many cystids in which no such plates existed. Loven and M. Aeumayr adduced the Triassic sea-urchin Tiarechinus, in which the apical system forms half of the test, as an argument for the origin of Echinoidea from an ancestor in which the apical system terminal. was ol great importance ; but a genus appearing so late in time, in an isolated sea, under conditions that dwarfed the other echinoid dwellers therein cannot seriously be thought to elucidate the origin ol pre-Silurian Echinoidea, and the recent discovery of an intermediate form suggests that we have here nothing but degenerate /oral u/itA descendants of a, well-known Palaeozoic family (Lepidocentridce). /wetter pore. ut to pursue the tale of isolated instances would be wearisome. e . calycinal theory is not merely an assertion of certain homolo■radial. gies, a few of which might be disputed without affecting the rest: i goveins our whole conception of the echinoderms, because it fPS^ implies their descent from a calyculate ancestor—not a*“crinoidphantom that bogey of the Sarasins, but a form with definite 1 rates subject to a qumqueradiate arrangement, with which its lr internal organs must likewise have been correlated. To this in{fral/ctsai a d lau sd,1 the fndTn P L to ebe opposed. ory the revelations of the rocks are more and more *believed C n Ct Ther ln hJ^ lh fp. fy--: opposition to There the calycinal theory has the f Semon Fl0 C te, free manv vnn!. °7 ° alwaystobeen ls fs re“ urc-™™g nn 'regm!rT™^ S S B l Echinoderms. A, a i i y,. ° P pared to ascribe an ancestralhave character the (Salenia)-, C develomn'>onhinvllw^ J. with a sur-anal plate p h a nS Th J ab ence of an {Zoroaster). k °P iurid (Amphiura); D young starfish thaf 7^?a i s ‘ mmel ® apical system of plates ; the fact i • a ,, 0 y er recen try has^not affected the generative organs, as it r i t classes ; the well-developed muscles of the B) ossess a n ‘Wanfe’ ./ sub-central plate (the body-wall, supposed to be directly inherited from some worm-like h ^v ices or, t re presence on the inner walls of the body in the family It is also the +wght te ldentlfied W1th the centro-dorsal. ynap i ae of ciliated funnels, which have been rashly compared to e excretory organs (nephridia) of many worms; the outgrowth Salt Si “ rom e rectum m other genera of caeca (Ouvierian organs and respiratory trees), which recall the anal glands of the Gephyrean everythin^ f °/-f sea-lIrchm or starfish as corresponding in worms, the absence of podia (tube-feet) in many genera, and even t0 he eea fl0OT e radial water-vessels in Synaptidae; the absence of that ‘ - "ith the ^ o theo has b r peculiar structure known in other echinoderms by the names , y "' ‘ vigorously opposed, notably by Semen axial organ, “ovoid gland,” &c. ; the simpler form of the (»P. al.), who saw m the holothurians a nekrer apploS S the aiva all these features have, for good reason or bad, been