HOLOTHURIAN SPICULES 



895 



class generally. 1 But a microscopic examination of their integument 

 at once brings to view the existence of great numbers of minute 

 isolated plates, every one of them presenting the characteristic re- 

 ticulated structure," which are set with greater or less closeness in 



FIG. 680. Holothurioidea : I,Stichopus Kef erst ei nil ; , calcareous 

 plate of same; 6, c, calcareous plates of Holothuria vaffabunda ; 

 (1, the same of H. inh<il>His\ e, the same of H. botellus; f, of H. 

 pardalis : g, of H. edit fin. 



the substance of the skin. Various forms of the plates which thus 

 present themselves in Holothuria are shown in fig. 680. 2 In the 

 Synapta, one of the long-bodied forms of this order, which abounds 

 in the Mediterranean Sea, and of which two species (the 8. digitata 



FIG. 681. Calcareous skeleton of S//>Hij>t : A, plate imbedded in 

 skin ; B, the same, with its anchor-like spine attached ; C, anchor- 

 like spine separated. 



and >V. inhcerens) occasionally occur upon our own coasts, 3 the cal- 

 careous plates of the integument have the regular form shown at A, 

 fig. 681 ; and each of these carries the curious anchor-like appendage, 

 C, which is articulated to it by the notched piece at the foot, in the 



1 For an account of a very remarkable form see Moseley ' On the Pharynx of an 

 unknown Holothurian, of the family Dendrochirotae, in which the calcareous skeleton 

 is remarkably developed,' Quart. Jourti. Microsc. Sci. n.s. xxiv. p. 255. 



2 For figures of the spicules of British Holothurians, see Bell, Catalogue of the 

 British Echinod&rms, London, 1892, pis. i.-vi. 



3 ' On the spicules of Syiiapta, together with some general remarks on the archi- 

 tecture of Echmoderm spicules,' consult R. Semon, Mitth. Zool. Stat. Ne^el, vii. 

 p. 272. An excellent summary of our knowledge of the spicules of Holothurians is 

 given by Prof. Ludwig in his volume in Bronn's TJiierreich, pp. 35-61. 



