<§> 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 Holothurioi'dea 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 respii-atory systems, will be fully treated hereafter. 



§78. 



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

 (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 difi"erent 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 mouth, and opposite the ambulacral Astrogonium, they are valvular and without a 

 rosette, a row of ambulacra having special pores. pedicle ; see Mailer 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 PFiegmann's Arch. 1842, I. p. -' The pedicellariae of Echinus were, at first, 



5.5, Taf. n. fig. 10. The corpuscles found by taken for parasitic Polypi by O. F. Mailer (Zool. 



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



Taf. HI. No. vn. fig. 37, a. b.) in the marine Hist. Nat. des Anun. sans Vert^bres, II. p. 75. 



sand of Vera Cruz, and figured under the name More recently, Agassiz {Valentines Monogr. loc. 



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



parts of the skeleton of Echinus. This wiU be young individuals. The researches of De/Ze CAzo/e 



evident from comparing them with the calcareous (Memor. sulla storia e notom. degli Anim. senza 



corpuscles figured by Foien^m (Monogr. loc. cit. Vertebr. n. 1823, p. 324, Tab. XXin.) 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. contained in the Royal Coll. of Surgeons, all doubts as to the real nature of these organs. 

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



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

 like pedicellariae. In Asteracanthion, they have PI. IV.), and by Erdl (fViegmann's Arch. loc. 

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



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

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

 regards as Pedicellariae on the skin of Valuta 



