kc;hinoi)ERMs. 



33 



'I'liis is very near the analysis of the opliiuraii Irmn ( 'iildnii Island, which is not far from the 

 h)cality of this liolothuriaii. The coinciileiice is very stril\iiif^. 



In tlie specimen represented hy analysis 2 the proportion of inorganic matter was so small 

 that good results could hardly be obtained. Tiie otlier two analyses were also made with alto- 

 gether iiiadecpiate material. These analyses, however, sliow that the small inorganic portions 

 of the holotlmrians are relatively rich in phospiiatic matter and in magnesia. The difliculties 

 of iliscussing them intelligently are like those of discussing the woiin tulx's and the axes of 

 alcyonarians. In Trochosfoma there are l)rown spots, wliich were already known to be phos- 

 phatic, although quantitative analyses of them seem to be lacking. The true cliaracter of such 

 bodies can be determined only by an elaborate investigation upon abundant material, a task 

 which lies outside of our main problem. 



Two analyses of holothurians are already on record, as follows: 



1. Stichoptis regalis. Locality not stated; analysis by (). Biitsf-hli. K. Gesell. Wiss. Gottinsrcn .\l)h., \o. 3, 1908. 



2. Ash of the epidermis ("lederhaut") of a large holothurian. species and locality not stated; analysis by Uilger. 

 I'tlttger's Archiv f. Physiologic, vol. 10, p. 212, 1875. 



Old nnalgses of holothurians. 



These analyses, together with ours of nolothuria, show that the hard parts of these animals, 

 like those of the other echinoderms, are distinctly magnesian. Although definite data are 

 wanting, it seems probable that Hilger's specimen came from warmer water than that analyzeii 

 by Biitschli. The sodium salts are of course extraneous. 



6. SUMMARY. 



From the evidence now available it seems almost certain that the inorganic constituents 

 of any echinoderm wall have the composition of a moderately magnesian limestone. There may 

 be exceptions, but none has yet been found. The five tables — for crinoids, sea urchins, star- 

 fishes, ophiurans, and holothurians — all tell the same story, and with remarkable unanimity. 

 Furthermore, the proportion of magnesium carbonate appears to be a function of temperature, 

 the organisms from warm waters being richer in it than those from cold waters. The exceptions 

 to this rule are few and may be only apparent, for cold or warm cmTents and varymg depths 

 of water account for nearly all irregularities. Schmelck's analyses of starfishes from the North 

 Sea are the most troublesome to explain. 



The sea urchins seem to be a little poorer in magnesia than either of the other groups, hut 

 the analyses are fewer and therefore less conclusive. Silica and sesquioxides are probably 

 altogether extraneous, although it is possible that small quantities of them may really belong 

 to the organisms. As shown by Meigen's reaction, all the echinoderms studied are calcitic, and 

 no evidence of aragonite in them was found. 



The temperature relations shown by the analyses offer an interesting biological problem, 

 with which we can not undertake to cope. It is not due to ditt'erences of composition in the 

 solid matter of sea water, for that is practically uniform the world over. In all the great oceans, 

 and even in minor bodies of water like the Mediterranean, the Baltic, and the Black seas, the 

 proportion of magnesia to lime is very nearly if not actually constant. In gaseous contents 

 and especially in carbon dioxide the waters vary; the gases being more soluble in cold than 

 in warm water. Whether this fact has any relation to the phenomenon under discussion we 

 can not attempt to say. We can only report the facts and leave their biological discussion 

 to others. 



