History of British animals - University of Guam Marine Laboratory

( 475 )ANOCYSTI.In those speciesin which the mouth and ventare at opposite endsof the axis of the animal, the body is globular or hemispherical, and dividedinto ten compartments by ten avenues of pores. The avenuesapproach hi pairs, making five of the compartments smaller than theothers with which they alternate. The smaller compartments consistof a double row of plates, united to each other by a zig-zag line, andto the larger compartments by a straight subserrated suture. Eachplate is covered with tubercles, on the surface next its fellows, in thesame compartment, but on the surface towards the opposite side, it isperforated with pores, in pairs, and arranged in oblique lines, with anoral direction. The portions of the plate, with the pores, are frequentlycompound. These plates increase in size, from the mouth to themiddle of the body, where the avenues of the pores are at the greatestdistance, and then decrease to the pelvis, where the pores approach,and terminate in a pentagonal costal plate. In the inside of the mouththere are five plates perpendicular to the margin, and perforated in themiddle, from which the smaller compartments take their rise. Thelarge compartments likewise consist of a double row of plates, unitedby a zig-zag line, covered with tubercles without pores, widest in themiddle of the body, and terminating in the five plates of the pelvis,one of which, termed the wart, is curiously puckered, and all of themhave a large perforation. These plates form the ring of a circularspace, covered by a tough skin, with tubercles, and perforated in thecentre by the vent. Around the mouth there is likewise a circularspace, formed by a tough muricated skin. The whole isbody coveredwith an iutegument, more or less intermixed with muscular fibres.The appendices of the skin are of three kinds. 1. The pricklesare ofdifferent sizes, and are seated on the convex surface of the tubercles,which are received into their concave bases, thus forming a ball andsocket joint, surrounded by theintegument, and put in motion by itsagency. These serve the purpose of defence, and assist locomotion.Their structure is radiated from the centre, with distinct traces of concentriclayers of growth. Mr Haidinger,in his translation of Mohs'sMineralogy, vol. ii. p. 91, has stated, that, in a fossil state, " everyone of the spines of Echini consists of a single individual (RhombohedralLime Haloide) perfectly cleavable, and the axis of which is parallelto the axis of the spine. But, what is still more remarkable, thespines of these animals possess the same property,even in recentspecimens of the latter, and it appears, that the carbonate of lime crys-