§ 78. THE ECHINODERMATA. 81 



chiefly locomotive; for from them numerous points are prolonged, by 

 which they adhere to objects, and to which they become afterwards fixed 

 by their sucker. They are covered with ciliated epithelium, and their 

 suckers are made firm by a coarse calcareous network. Elongated cal- 

 careous corpuscles of the same nature are found also in their walls, — 

 some branching and others hook-like. '"*' 



V. With those Holothurioidea which have them, they have a more or 

 less complete sucker, and are scattered irregularly over the entire surface 

 of the body, or disposed in regular rows. Usually very short, they can be 

 retracted deeply in the skin ; but they are capable of equal prolongation, 

 and thus perform well the function of suckers. "'> 



The ambulacral vesicles, which are intimately connected with the circu- 

 latory and respiratory systems, will be fully treated hereafter. 



§78. 



With the Echinoidea, and Asteroidae, there are other movable organs 

 (pedicellariae), which, scattered over the surface of the body, are prehen- 

 sile, and used in a pincer-like manner. With the Asteroidae, they usually 

 consist of two delicate forceps-like pieces (pedicellariae forcipatae), or of 

 two large valvular flaps (pedicellariae valvulatae). Generally they are 

 not pediculated.'^^ Those of the Echinoidea have been carefully studied 

 in Echinus. They are numerous, and occur for the most part about the 

 mouth, presenting three different forms : 1. Those composed of three 

 short, lenticular pieces (pedicellariae gemmiformes). 2. Those formed of 

 three long delicate pieces, laterally denticulated (pedicellariae tridactyli). 

 3. Those with three laterally denticulated spoon-like pieces (pedicellariae 

 ophiocephali). They are supported by a base of calcareous, reticulated 

 substance; and in the Echinoidea, always rest upon a stalk, the lower part 

 of which contains a cylindrical, calcareous nucleus, while the remaining 

 portion is soft, and capable of a spiral contraction. ^'-^ Here also they are 

 covered with ciliated epithelium, and can, by means of movable processes, 

 seize hold of objects, which, being passed along, may be conveyed even 

 from the dorsal surface to the mouth. 



near the moutli, and opposite the ambulacral Astro^onium, they are valvular and without a 

 rosette, a row of ambulacra having si)ecial pores. pedicle ; see Mii/ler and Troschel, loc. cit. p. 



5 See Valentin, Monogr. loc. cit. p. 37, PI. IV. 10, Taf. VI. fig. 3-6. 



v., and Erdl in fViegmann's Arch. 1842, I. p. 2 The pedicellariae of Echinus were, at first, 



55, Taf. II. fig. 10. The corpuscles found by taken for parasitic Polypi by O. F. Milller (Zool. 



Ehrenberg (Abhandl. d. Berl. Akad. 1841, p. 324, Dan. I. 1777, p. 16, Tab. XVI.). See Lamarck, 



Taf. III. No. VII. fig. 37, a. b.) in the marine Hist. Nat. des Anim. sans Vert^bres, II. p. 75. 



sand of Vera Cruz, and figured under the name Wore recently, Agassiz (Va/entin^s Monogr. loc. 



of Spongolithis uncinata, are only the cruciform cit. p. 51) has expressed the opinion that they were 



parts of the skeleton of Echinus. Tliis will be young individuals. The researches of TJe/Ze Chiaje 



evident from comparing them with the calcareous (Memor. sulla storia e notom. degH Anim. seiiza 



corpuscles figured by Valentin (Jlonogr. loc. cit. Vertebr. II. 1823, p. 324, Tab. XXIII.) and of 



PI. V. fig. 65). Sars (Beskrivelser, &c., p. 42, Tab. IX.) upon 



6 Catalogue of the Physiol, series of Comp. Echinus, Cidaris, and Spatangus, have dispelled 

 Anat. contamed in the Royal Coll. of Surgeons, all doubts as to the real natm-e of these organs. 

 London, IV. 1838, p. 196, PI. XLI.X. fig. 3-5. Very correct descriptions of them have lately been 



1 With twirfia, there are, however, tliree tongue- published by Valentin (Monogr. loc. cit. p. 46, 

 like pedicellariae. In Asteracanthion, Ihe^y ha.ye PI. IV.), and by Erdl (IVieg7nann^s Arch. loc. 

 a soft pedicle. In Asteropsis, Stellaster, and cit. p. 49. Taf. II. fig. 1-9).* 



*[5 78, note 2.] See Adams (Ann. of Nat. vespertilio ; he thinks, therefore, that they are 

 Hist. VIII. 1851, p. 237), who has found what he independent parasitic organisms. — Ed. 

 regards as Pedicellariae on the skin of Valuta 



