ECHINODERMATA. 



[ 219 ] 



ECHINUS. 



See ACEPHALOCYST. 



BiBL. Kiihn, Ann. des Sc. nat. 1 ser.xxix. 

 p. 273 ; Siebold, Wiegmann's Archiv, 1845. 

 ii. p. 241, and Siebold and KoUiker^s Zeitschr. 

 iv.; Gluge, yinn. des Sc.nat. 2 ser.viii. p. 314; 

 Owen, Hmiterian Lectures,!, p. 46; Dujardin, 

 Helminthes, p. 635; Huxle}^, Ann. Nat. Hist. 

 2 ser. xiv. p. 3/9. 



ECHINODERMATA.— A class in the 

 Animal Kingdom, including the species of 

 star-fishes {Asterias), of sea-hedgehogs or sea- 

 eggs {Echinus), of sea-slugs {Holothuria), 

 &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 circulation 

 and respiration ; sexes not always distinct, 

 and external generative organs never present; 

 disposition of organs generally quinary; body 

 generally radiate or globose, sometimes cy- 

 lindrical; nervous system forming a ring 

 generally surrounding the mouth and giving 

 off radiate branches. 



A cutaneous skeleton usually exists as a 

 network of calcareous corpuscles (PI. 37. 

 fig. 1), or numerous calcareous plates, 

 pretty regularly perforated so as to form a 

 solid continuous network (PI. 37. fig. 2). 

 The plates are sometimes moveable, at others 

 connected by sutures ; some are perforated 

 with larger apertures — the ambulacral pores ; 

 they are often furnished with calcareous 

 appendages,tubercles, prickles, spines, hooks, 

 &c. ; some being imbedded in the leathery 

 integument itself. Many of these appendages 

 form beautiful microscopic objects, and pos- 

 sess very remarkable analytic power (see 

 Echinus, Synapta and Shell). 



The muscular svstem consists of distinct 

 flattened primitive fibrils and bundles, 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 very 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 

 leathery or calcareous covering of the body, 

 and acting as organs of adhesion andasfeelers. 

 In the Echinidea {Echinus-iwoaily) and 

 Asteridea (^s^ma^-family), other curious 

 appendages occur, called Pedicellarim (PI. 37. 

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

 neous surface, and consist of a forcipate or 

 valvular apparatus, acting as organs of pre- 



hension. The Pedicellarice of the Asteridea 

 usually consist of two long forceps-like or 

 two broad valvular arms, and have hence 

 been divided into forcipate and valvate Pedi- 

 cellaricB. They are mostly without a stalk. 

 In the Echinidea {Echinus) they are most 

 numerous around the mouth, and 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. Ophi- 

 ocephalous,with three spoon-shaped laterally 

 toothed arms. These PedicellaricB contain a 

 reticular calcareous 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 spirally retractile. The Pedi- 

 cellarice 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 situated on the posterior 

 half of the body, or near the anal region, can 

 gradually pass it 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 system, is also present, into the 

 structure of which and other particulars we 

 have no space to enter. 



BiBL. Siebold, Vergleich. Anat. p. 74 ; 

 Cycl. Anat. and Phys. (Sharpey) ii. p. 30; 

 Agassiz, Monograph d'Echinod.viv. etfoss.; 

 Valentin, Monogr. d'Echinoderm. livT. iv. ; 

 Forbes, His^. of Brit. Starfishes, ^'c; Miiller 

 and Troschel, System d. Asteriden ; Miiller, 

 Abh. d. Berl. Akad. 1846-1851 (Huxley, 

 Ann. Nat. Hist. 1851 (viii. p. 1). 



ECHINORHYNCHUS, Miiller. — A 

 genus of Entozoa, of the order Sterelmintha, 

 and family Acanthocephala. 



Char. Body cylindrical or sacciform, some- 

 what elastic, transversely rugose, obtuse at 

 both ends ; furnished with a reti*actile pro- 

 boscis, which is armed with from one to sixty 

 regular transverse rows of recurved spines; 

 sexes distinct ; no mouth. 



The species, which are very numerous, 

 many microscopic, reside in the alimentary 

 canal, most commonly of fishes, less so in 

 that of mammals, and stiU more rarely in 

 that of birds. 



BiBL. Dujardin, Hist. nat. d. Helminth. 

 p. 483 ; Cloquet, Anat. d. vers Intestin. 



ECHINUS, Lam.— A genus of Echino- 

 dermata, of the family Echinidea. 



