118 
REPORT- 1847. 
these to a much greater degree of thinness than Prof. Valentin seems (from 
the descriptions and delineations which he gives) to have succeeded in ob> 
taining*. My own investigations, too, have been carried into all the leadiDg 
groups of the class; and I had myself determined, and demonstrated to 
others, the structure of their skeleton, before the Monograph of Prof. Va¬ 
lentin, published in 1842, had rcache<l this couotrj’, 
107- The elementary structure of the skeleton of the Echinodemata may 
be described as a network, cotupoacd of calcareous and animal matter iuQ- 
mately united; the former, however, being greatly predominant. In tla 
network, the interspaces or areola?, and the solid structure which surrounds 
them, may bear an extremely vwiable j)roportion to each other; so that ia 
two masses of equal size the ouc or the other may greatly predominate, wd 
the texture may have either a remarkable lightness and porosity, or a cos- 
siderablc degree of compactness and brittleness. Wo may perhaps taketb 
plates making u]> the testa of the ICchinus os presenting to us the most typ* 
, tncthwl mny be iweful to others, Itliink it dewnblehne'" 
aetail it. The procmis adoptnl id this country for mshinp thin sections jf hone, fflaril 
acc., 13 employee . with A aiigiu varUiion required by the peculiar nature of the »obian« 
operated on, and ia pr.nciiaed n* follows. A thin slice of the »bell or spino b cut off "ith* 
tone saw, flatteued on one side with e file, and tlieu poIMiod with water upon a » Waia-of- 
♦1 w f""®; should then be well dried : and when any portion afthe skelewnof 
Uie JSc/mwdermaia is beiiiK opcn-nlrd on, core must be tnlcon that the drying is so eomplrtea 
Iprv tUiriiiff the polislilng Inin the spsvM of ia 
for Lml rnH®'r • ’! ''*■*' ’* sections worm near a fire orovtr slamp 
an ntTrfJl.- "■ previously hardened by bolliiig, sou toaUsia 
Is then to ho mclled upon a sUp of el«s, and made »f«m» 
‘ *•'»* ••«*/ bare formed in it will Ipnf* 
ration of thin *^*'*"15 ^ P**'*'* of K««« importsiice in the pr*))!- 
indented bv the nlu 
boiledlS ior. ‘=bip. If it be too .aft, itdieuld b 
fluid balsam When if J C'"** *«heiicd by Iwinp inched and then rahed with mote 
polished sidL bein tbe right consUtcncc. the sertion should belaid uponlUiurfece.IlK 
be gradually wttrLdaaU^d.o^*^ 
of bubbles; and Uw «ct5?n^l« ^ iflwcvrr to avoid beating it so far a* |o ocmion the fi>fin«« 
piece of ordinary-lh,m ..r r« ° “P®" 'I'C liquefied W«in. 
of balsam shall be iinSCn.., ^**'* ** reijuislte is, llial a Ihhi l*yef 
aeraing to attach the two the pollahcd side of tlie section and tH* 
glass, so 83 to fores m.t *®Ii’ “"*1 *1''^ action may be firmly pressed down opso 1^ 
skeleton of the /jL-AiWcrtun^f^h balsam from between them. When say portion olU« 
substance shall be lalurated ' 
tcrstices by capilUrv aiti-a -i, 'c balsam, which will bedrswn npinuiH^'r 
gcuri^prcsLddown^imon .1^® wpi'llod iu sufficient qnnntity. The section !«•« 
by the hardened balsam }. ? • ** 'eft «o cool. tW purtwse of the Mtnr^ 
»L .hi,*.”!':;™,",” ‘“srxi •‘■-5'^"',^: 
same tenuity. If ihe I,a I..,,,, i.- ^ .'t* bone, and thus to allow It to be rHuced wi 
bris resulting from Ihe subsi-mio’*Jr'n^,!l* '“'*‘''*"‘•5' bardeued, it will Isy hold ^ the 
opakc matter. If. on the oih^r K-. iiifersdces will thus be filled up " 
the secUon, when r^m, ““ 
in part or as a whole Sumuitinn. *'! disposed to sepame from tbs gh*‘''‘V 
per consistence, the s'cctioifinav fh m* '** balaanj hare been hardened to ihep 
upon the stone,’ until it ‘I®*®- «» first with . file, and 
placing it occasionally tin, Ipr th* • ^^^blslto thinness, which oust be ; 
can oi^y I« duScd^riU hiVhn,?'^^ 
very little more rubbino wn.it f pevffvnon when the thinness of the section b sufh 
management after m.ioh practice ' f ‘^isian only he attained by 
18 to be gently wanned ri,.,i ...wT r tbc aecttoo js sufficiently reduced, the slip ^ 
Of vapour, which, wl.en on^ ,?nr * ? f' 
be got rid of. A small bit of I '® of thrstmcHire, cm 
ihe preparation is complete ^ 
