1250 METABOLISM OF LIPOIDS, STEROLS, [pt. m 



phosphate when the P2O5/CO2 ratio is o-i. Biitschh, moreover, re- 

 ports that adult echinoderm spicules contain phosphate. 



The distribution of phosphorus in the Dendraster egg is, it may be 

 noted, widely different from that in the hen's egg. Instead of the 

 great stores of lipoid and phosphoprotein phosphorus, there is only a 

 small proportion of these bodies, while a prominent place is taken by 

 the various forms of water-soluble phosphorus and nuclein phos- 

 phorus. The phospho-protein phosphorus falls during development, 

 perhaps indicating that it is playing a similar part in both cases. The 

 figures for the starfish egg in Table 1 76 show no absorption of phos- 

 phorus from the sea-water, so that the practice cannot be universal 

 among echinoderms, but both organisms provide almost enough 

 nuclein phosphorus in their eggs for the requirements of the embryo. 

 This fact has already been considered in Section 10. The constancy 

 in lipoid phosphorus in Dendraster and the fall in Patiria may perhaps 

 be related to the fact that the initial amount is small in the former 

 case and large in the latter. Many instances of this have been given 

 in this section, and we mav summarise them as follows : 



This probably indicates two main appropriations of lipoid [a] a funda- 

 mental quota which no egg can do without, and which is built up 

 into the cell-membranes and other structures of the finished embryo 

 without change, and {b) a further store, which in terrestrial eggs may 

 be very great, which is broken down during development yielding 

 phosphorus in a form available for calcification or other uses. 



It is interesting to calculate the contribution of phosphorus made 

 to one echinoderm e.gg by one spermatozoon. In the case of Den- 

 draster we found i gm. dry weight of egg to contain 8 mgm. of total 

 and 2 mgm. of nucleoprotein phosphorus, and this value may be 

 accepted as being of the same order in various echinoderms. Accord- 

 ing to Page one million Arbacia eggs weigh when dried 0-124 gm., so 



