ECHINODERMATA. 



[ 274 ] 



ECIIIXODERMATA. 



coming partially converted into fatty or 

 calcareous matter ; or the entire contents 

 become amorphous and granular, the hooks 

 remaining longest unaltered, but finally dis- 

 appearing also. 



See T^NiA. 



BiBL. Kuhn, Ann. Sc. Nat. 1 ser. xxix. 

 273; Siebold, Wiegm. Archiv, 1845, ii. 

 241, and Siebold und KnUiker^s Zeits. iv. ; 

 Dujardin, Helminth. 6:55 ; Cobbold, Paras. 

 112. 



ECHIXODER'^MATA. — A Subkiug- 

 dom in the Animal Kingdom, including 

 the star-fishes (Asterias), the sea-hedgehogs 

 or sea-eggs (Echinus), the sea-slugs (IIolo- 

 thuria), &c. 



The Echinodermata are marine animals, 

 ' with a coriaceous or calcareous integument ; 

 alimentary canal distinct, suspended in the 

 cavity of the abdomen, and with either one 

 or two orifices ; distinct organs of circula- 

 tion and re.'^piration ; sexes usually distinct, 

 and external generative organs never pre- 

 sent; disposition of organs generally qui- 

 naiy ; body usually radiate or globose, 

 sometimes cylindrical : nervous systemform- 

 ing a ring generally surrounding the mouth 

 and giving oft" radiate branches. 



A cutaneous skeleton usually exists as a 

 network of calcareous corpuscles (PI. 45. 

 fig. 1), or numerous calcareous plates pretty 

 regularly perforated so as to form a solid 

 continuous network (PI. 45. fig. 2). The 

 plates are sometimes moveable, at others 

 connected by sutures ; some are perforated 

 with larger apertures — the ambulacral pores; 

 thev are often furnished with calcareous ap- 

 pendages, tubercles, prickles, spines, hooks, 

 &c., some being imbedded in the leathery 

 integimient itself. Many of these appen- 

 dages, as well as the calcareous corpuscles, 

 form beautiful microscopic objects, and 

 possess very remarkable analytic power 

 (see Echinus, Synapta, and Shell) ; they 

 are also of importance in classification. 



The muscular system consists of distinct 

 flattened primitive fibrils and bmidles, not 

 transversely striated. The organs of loco- 

 motion exist in the form of little tentacle- 

 like organs, the so-called feet or ambulacra. 

 These are veiy contractile hollow prolonga- 

 tions of the cutaneous surface, expanded at 

 the end, and connected by the ambulacral 

 pores with contractile sacs (the ambulacral 

 vesicles) placed on the inner surface of the 

 leatliery or calcareous covering of the body ; 

 they act as organs of adhesion and as 

 feelers. 



In the Echinidea (-E'c///?H<s-family) and 

 Asteridea (Asterias-i'dmily), other curious 

 appendages occur, called pedicellarice (PI. 

 45. fig. 3) ; they are met with all over the 

 cutaneous surface, and consist of a forcipate 

 or valvular ap]iaratus, acting as organs of 

 prehension. The pcdicellarice of the Aste- 

 ridea usually consist of two or three forceps- 

 like or two broad valvular arms, and have 

 hence been divided into forcipate and val- 

 late pediccllarice. They are mostly without 

 a stalk. In the Echinidea (Echinus) they 

 are most numerous around the luouth, ani 

 have been subdivided, according to their 

 form, into : — 1. Gemmiform, having three 

 short lentil-shaped arms ; 2. Tridactyle, 

 having three long and laterally toothed 

 arms ; and 3. Ophiocephalous, with three 

 spoon-shaped laterally toothed arms. These 

 pedicellarice contain a reticular ddcareous 

 mass as a basis, and in Echinus are placed 

 upon a stalk, the lower portion of which 

 encloses a calcareous nucleus, whilst the 

 other portions are soft, extensile, and spi- 

 rally retractile. The pedicellaria of Echinus, 

 which are partially covered with ciliated 

 epithelium, can seize larger or smaller bodies, 

 and pass them from one to the other ; so 

 that an object grasped by one of them situ- 

 ated on the posterior half of the body, or 

 near the anal region, can be gradually 

 passed on towards the mouth. 



The abdominal cavity of the Echinoder- 

 mata is always filled with sea-water, kept 

 in motion by cilia covering the intestinal 

 canal. 



A true blood-vessel system, as well as the 

 water-vessel or ambulacral system, is also 

 present, into the structm-e of which and 

 other particulars we have no space to enter. 



In their youngest state, the Echinoder- 

 mataconsist of infusoria-hke bilateral beings, 

 without organs, and swimming by means of 

 cilia on the surface. 



BiBL. Siebold, Vergl. Anat. 74 ; Sharpey 

 Cycl. Anat. ^- Ihys. ii. 30 ; Agassiz, Echi- 

 nod. viv. ct foss. : Valentin, Echiuoderm ; 

 Forbes, Br. Starfishes-. Miillerand Troschel, 

 Asteriden;^l.\x\\>ix, Berl. Ahh. 1846-1851; 

 Huxley, Ann. N. H. 1851, viii. 1 ; Gosse, 

 Mar. Zool. i. 54 ; V. d. Iloeven, Zool. and 

 Sujypl. (Leuckart) ; Gegenbaur, Vergl. An. 

 205 ; Herapath, Qu. M. J. 18(i5, 175 (pedi- 

 cellarice) ; Frey, BedecJi. u-irbcll.Th. ;Koren, 

 Arch. Scandinar. i. 166,449; Norman, Ann. 

 N. II. 1865, XV. !)8 ; Stewart, Qu. M. J. 

 1871 ; Nicholson, Zool. 1878, 181 ; Sladen, 

 Ann. N. H. 1880, vi. 101 (pedicellarice). 



