A treatise on zoology . ases. Nor need more besaid as to the enlargement of certain radii ( Fuocrimis), thebisection of others ( Heferocrinus), and so forth, since in thesecases the outwardly symmetrical appearance of the cup usuallyremained unaltered. But certain factors, probably of physicalenvironment, such as currents and direction of food-supply, orpossibly connected with locomotion, have at different times pro-duced similar results in different families. A bending over of thecup, accompanied by diminution of certain radials, was commonin Eugeniacrinidae, as well shown by Jaekel (
A treatise on zoology . ases. Nor need more besaid as to the enlargement of certain radii ( Fuocrimis), thebisection of others ( Heferocrinus), and so forth, since in thesecases the outwardly symmetrical appearance of the cup usuallyremained unaltered. But certain factors, probably of physicalenvironment, such as currents and direction of food-supply, orpossibly connected with locomotion, have at different times pro-duced similar results in different families. A bending over of thecup, accompanied by diminution of certain radials, was commonin Eugeniacrinidae, as well shown by Jaekel (1891). In theremarkable Calceocrinidae the crown was bent towards the rightposterior interradius, and far-reaching changes brought about inboth cup and arms (p. 148). Even in an unattached species,apparently of Agassizocrinus, similar growth of one side took place at the expense of the other. Thesecases are comparable to the irregu-lar Eublastoids. Concomitant with modificationsin the dorsal cup were modifica- Amb lAtnb. tions in the Tegmen. Just asbrachials entered the cup, so theircovering-plates (xVmb) entered thetegmen, prolonging the food-grooves over its surface. And cor-responding to interbiachials in thecup, there arose intcramV)ulacrals(iAmb) in the tegmen (). Other changes that took ])laceare ditficult to describe withoutraising the question of the homo-logy of the ])Iates covering themonth. In .lufedon five inter-radial phitos (()) are (Uvol()])edbefore the radials and at the same time as the basals, uj)nii wliiclithey rest (Fig. XXX ill. I). Uetween these two circlets ap|)earthe radials, u|)()ri tlu^ shouhhus of whicli the five adoral interradialsthen rest (Fig. XXXIII. 2), forming a ])yraniid closed over tliooral centre, but soon opening at the apex to expose the entninceto the mouth (terita(Miiar vestibuU;)- l* posterior of th(»s(^ platessurrounds the hy(lroj)ore. At a nioi(^ advanced stage tliev becomeseparated from the radials by aml)uhicrals and inter
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
