RAD I ATA 



G93 



Enciunts 



The rentacrimts, however, must not be regardeo. »s the true i,,pc of the Crinoid order, but rather afl a link of 

 tiansition which connects it with the higher forms of Echinodermata. Fur the bulk of the group is made up of 

 the very numerous tribe of Evcrinites, which seems to have been in many respects of lower 

 organization, connecting the free Echinodermata with Zoophytes. The body and jointed 

 stem exhibit a rounded instead of a pentagonal form ; the latter is usually destitute of se- 

 condary arms ; and the principal branches do not ramify with the same minuteness as those 

 of many Pentacrini. The stalk seems to have been attached by a sort of spreading root, re- 

 sembling that of many Corals ; and we must therefore believe this tribe of Crinoidese to hare 

 been entirely fixed. It contains a numerous series of forms ; some of them almost re. 

 semhling Stalked Echini, whilst others in like manner seem to connect the order with the 



two following. 



II. Ophiurid.e. These Star-fishes are so named from the long serpent- or worm-like arms, 

 which are appended to their round, depressed, urchin-like bodies. Although commonly as- 

 sociated w tli the true Star-fish, they are very distinct in their structure. The viscera are 

 entirely confined to the central disk ; and the arms are solid, like those of the Crinoideoe, 

 t£)ft~^R~-— fc~5^\ being covered with a muscular integument, by which the joints are caused tomove freely upon 

 one another. On the other hand, they differ from the Oiuoidese in having but a single aper- 

 ture to the digestive cavity ; and also in the position of the ovaries, which are here situate, 1 

 within the disk, opening by separate orifices near the base of the arms. The arms are some- 

 times simple and undivided from their base to their free extremity, gradually tapering to a 

 point, as in the ordinary Ophiurw ; whilst in Kurt/ale they ramify minutely, dividing regu- 

 larly into branches, which again subdivide so as to form a most complex series of appendages. 

 The arms in this order very commonly bear scales or spines on their surface ; and these 

 appear to be of great use to the animals, their roughness giving to the arms a point of rest, from which 

 they can push the body onward in any direction. Their movements are very active, in comparison with thosf 

 of Star-fishes ; and as they depend upon their spines for locomotion, they may be properly designated Spini. 

 grada. Their eirrhi are not sufficiently developed to assist in locomotion ; although those near the mouth are 

 enlarged into ttntacula, which seem to draw the food towards the orifice. 



III. In the Astekiada:, or true Star-fishes, the real arms altogether disappear ; the raws being merely lobes of 

 the body. In some instances there is scarcely any central disk, the body being almost entirely divided into raj B ; 

 whilst in other cases there is but a slight division of the margin of the disk. The general structure of the 

 Asterias, which is the type of the order, is described in the texl (p. 639). The movement of these animals is 

 sluggish, and is accomplished by means of the eirrhi, which form rows along the under side of the rays, and 

 which serve as suckers for taking an attachment to any solid body, lb nee the order may be designated CtBRtn. 

 grada. The development of the Star-fishes has been recently studied by Sars and others ; and it appears that 

 they are attached in their embryonic condition, by a sort of footstalk divided at its base into three lobes. 

 This pedicle contracts, however, as the disk is developed, and is at last entirely withdrawn into the body of the 

 animal. A trace of it still remains, however, in what has been termed the madreporiform tubercle. 



IV. The order ECHINIDA corresponds with ( uvier's Second Family of PediceWita (Text, p. C40). The type of the 

 order is the genus Echmv . 

 in which the shell is of globu- 

 lar form, Having the oral 

 orifice at one pole, and the 

 anus at the other. The 

 mouth is furnished with a 

 complex dental apparatus 

 (C, Fig. 2) ; and there is a 

 1 alar intestinal tube, 

 which makes two turns 

 Within the shell. The ova- 

 ries open i>_\ distinct orifices 



around the anus. The 

 movement of these animals 

 is partly accomplished by 



their spines, which are fre- 

 quently very large and 

 strong; and partly by thl ir 

 eirrhi. Which are always ca- 

 pable of being extended 



further than the spines, and 

 of taking an attachm 

 fixed ho. lies beyond. In this 

 manner the globular shell 



maj be drawn onwards in 'I * **!*, or s»t portion oi thtintmdtf«t ,; - ^MiipuJ»cjmi»t»icit«i^ f 4\i 



anj direction ; the mov< mem being effected bj the contraction ofthe tub, », but the bodj being supported uj>on 

 the spines. 1 rem this compound mode of progress! the > Cum Bphhobada. la 





Fin. 1, — A VA TOM V OF KrillM v : n , BODth, s'ir <• trrth tntl jnn», ', e\ b, Tmophnji* |. 



