44 



THE INORGANIC CONSTITUENTS OF MARINE INVERTEBRATES. 



In No. 14, the common edible slirimp of the Washington (D. C.) markets, the shell was so 



thin that the available material was too small for complete analj'sis. Only P2O5, 3.07 per cent, 



was determined. 



Reduced analyses of crustaceans. 



In addition to the foregoing analyses two more were made by Mr. Salkover of very minute 

 crustaceans, such as form a large part of the marine plankton. Two samples, each made up 

 of hundreds of individuals, were obtained from the U. S. National Musemn, as follows: 



1. Temora longicomis (O. F. Mtiller), from the coast of New England. Weight of dried sample, 0.6105 gram. 

 A copepod. 



2, Thysanoessa inermis (Kroyer), from Balena, Newfoundland. Weight of dried sample, 1.5973 grams. A small 

 shrimp. 



As the amount of material was insufficient for a thorough analysis, only three determina- 

 tions were made on each sample. They were: Loss on ignition, mainly organic matter and 

 water; phosphoric oxide; and residue insoluble in acid. The phosphoric oxide, P2O5, was re- 

 calculated into the form of tricalcic phosphate, Ca^P.Og, and wdth that adjustment the analyses 

 assume the following shape: 



Analf/ses of minute crustnci"'ns. 



These analyses show that the inorganic matter of these minute creatures consists almost 

 entirely of calcium phosphate, although more refined analyses on larger quantities of material 

 would doubtless show small percentages of other things. So far, however, it seems that these 

 very small organisms effect what is perhaps a primary concentration of the traces of phosphorus 

 that exist in sea water, and so, as food for the larger animals, they furnish the material from 

 which the skeletons of marine vertebrates are built. It is a familiar fact that vertebrate skele- 

 tons consist largely, although not exclusively, of calcium phosphate. 



