EIHAXG TILL K. SV. VET.-AKAD. HANDL. BAXD 18. AFD. IV. N:0 1. 35 



other operation has supervened, tbe retarded linal oue of deu- 

 tition, of breeding teetli and jaws. These massive parts in 

 the act of forming reqnire an abnndant snpply of organized 

 (•alcareous snbstance, and in tbe futnre imago tbey will de- 

 niand, powerfnl instrnnients as tbey are of prebension and di- 

 luinntion, tbe greatest possible faeility of motion. For tbeir 

 .sake, it will seem to me. in order to prepare for tbem pliant 

 siirroimdings, tbe onrrents of development are at last turned. 

 and calcareons matter just deposited in duly formed skeletal 

 constituents, is reabsorbed: remodelling in tbe Cidaridfe and 

 tbe Ecbinotbnrida^, all but dissolving in tbe otber gronps. 

 Tbis is tbe origin and bistory of tlie Inieeal niembrane. 



Tbe extension to wbieb tbe oral region of the corona in 

 lonseqnence of growtli and disintegration tbns is made flexible 

 and tbe stoma widened, is ditferent in tbe various gronps. If 

 tbe external diameter of tbe corona, measured in tlie direetion 

 of III— 5, is taken as 1, tbe corresponding diameter of tbe 

 stoma is as follows: 



In Cidaris papillata Leske 0,33; 



in Astbenosoraa varium Gribe 0,3o; 



in Arbacia pnnctulata Lmck. 0,5 9, A. australis Trosch. 0,5 2, 

 A. 0eqnitnberculata Blv. 0,5 1, Coeloplenrus Maillardi Mich. 0,4 7; 



in Ecbinometra Lucnnter L. 0,5 5. Heterocentrus mamil- 

 latns L. 0,5 4, Ecbinometra oblonga Blv. O.39, Stomopnenstes 

 variolaris Lmck. O.25; 



in Diadema saxatile L. 0.4 5. Ecbinotbrix Diadema L. O.ss; 



in Strongylocentrns grannlaris Say 0,3 4 ; 



in Spbperecbinns grannlaris Lmck 0,3 2; 



in Boletia Pileolns Lmck 0,34, Tripuenstes GratillaL. 0,2 8, 

 T. esculentus Leske 0,23; 



in Ecbinns esculentus L. 0,29, E. melo Lmck 0,24 ; 



in Amblypneustes pallidus Lmck 0,2 s, Salmacis sulcata 

 AoASS. 0,2 5, S. bicolor A gäss. 0,22. 



It is seen tbat tbe diameter of tbe stoma varies greatlv 

 in its proportion to tbat of tbe test. between 0,5 9 in Arbacia 

 and 0,2 3 in Salmacis. 



A\"bile in tbis m ann er a loss of calcareons snbstance goes 

 (in vcntrally. tbe number of coronal plates is augmented dor- 



