136 



HARD WICKE 'S S CIENCE - G O SSI P. 



known to be but the laroal stage of the common 

 Feather-star {Coma tula rosea), which maybe dredged 

 up in immense quantities in the quieter parts of our 

 sea-beds, but particularly so in the Irish Sea, and 

 from the bottom of the salt-water lochs which indent 

 the western coasts of Scotland. The Comatula is 



Fig. 132. Pear Encrinite {Aplocyinltcs rotiiiulus), from the Oolite 

 formation : 3, Body, or pelvis ; 4, Vertical Section of ditto, showing 

 Stomach. 



nearly related to another of our native free-moving 

 echinoderms, the Eiuyale, a genus which has a very 

 large geographical distribution. One living species 

 of Euryale, called palmifera (fig. 127), is evidently 

 nearly related to the common Brittle-stars (Ophi- 

 2iridic), which are distinguished by not possessing a 

 water-vascular system, and in being covered 

 with rows of limy plates. The commonest of 

 our British species is Ophiiira gninidata (fig. 

 129). Thus, we may pass from true living 

 Crinoids, stalked and jointed, to others which 

 are Crinoids only during the earlier part of 

 their lives. Thence to free-crawling Comatulas 

 and Enryales, and through the latter to the 

 Brittle-stars. This remarkable relationship is 

 still further indicated by the external limy 

 plates which cover or otherwise enter into the 

 structure of Crinoid, Feather-star, Euryale, 

 and Brittle-star alike. A similar blending of 

 the external shapes of allied forms may be seen 

 in another large group of Echinodennata — the 

 Star-fishes and Sea-urchins. Thus, beginning 

 with Asterias (noted for the body and arms 

 being covered with limy plates), we pass on to 

 the Cushion-stars, where the arms seem to 

 have been so stretched along their sides that 

 they have eventually grown together. Thence 

 we pass by such forms as Sciitella and Spaian- 

 giis, until we come to the true and abundant 

 Sea-urchins (Echiiiiis), so that the wide space 

 between the Encrinites and the Sea-urchins is 

 bridged over by a large number of inter- 

 mediate generic forms. Still more remark- 

 able is the fact illustrated by Haeckel and 

 others, that the young of all the Echinoderms 

 are so alike that it is most difficult to tell one 

 from another. All commence life as free- 

 swimming, worm-like larvte. 



The relationship between the Crinoids (or 

 Encrinites) and the other leading members of 

 Echinodermata is undoubtedly bound still 

 more nearly together by the intercalence of 

 several extinct groups. Thus the two extinct 

 orders, Cystidea and Blastoidea, were in some 

 degree intermediate between Encrinites and 

 Sea-urchins in a manner that we have no 

 examples of now living. The Tortoise-En- 

 crinites of the chalk (Marsupites), and the 

 Saccosoma of the Oolite (most probably allied 

 to the Feather-stars) are deejjly interesting, 

 inasmuch as they are stalkless fossil Encrinites. 

 We may regard the body and arms of an 

 Encrinite, of any species, as a kind of star- 

 fish attached to a jointed stalk. The base of 

 the Encrinite's body is called the "pelvis." 

 Hence the mouth is uppermost, surrounded 

 by the feathered arms— a position just the 

 reverse of that which would be assumed by a 

 star-fish, for the latter in crawling over the sea 



