1244 METABOLISM OF LIPOIDS, STEROLS, [pt. iii 



the brine-shrimp. But it is difficult to picture what may be going on 

 in the egg of the worm to produce these effects. It is, of course, to 

 be remembered that Ascaris is an organism living in very peculiar 

 circumstances^. 



Gephyrean eggs were investigated by Needham & Needham, on 

 the Californian echiuroid worm Urechis caupo. 



Here the lipoid phosphorus declines markedly, the total phosphorus 

 receives no accession from outside, and the nuclein phosphorus in- 

 creases considerably. 



When we come to the phosphorus metabolism of the echinoderm 

 embryo, we find ourselves in a region where a good deal of work has 

 been done, yielding at first unsatisfactory and controversial results. 

 Interest in the phosphorus distribution of the echinoderm egg arose 

 in the first instance out of the great increase in nuclear substance 

 during the early stages of echinoderm development, noted by Boveri, 

 Loeb and Godlevski. Thus the ratio of the total volume of the cell to 

 the volume of the nuclear material in the unfertilised egg is 550/1 but 

 in the blastula stage 6/1. There must then, said Loeb, be an increase 

 in absolute and relative amount of nucleoprotein, i.e. in purine bases 

 and nuclein phosphorus, and if the nuclein phosphorus increases, 

 something else must decrease, probably either phosphoprotein or 

 lecithin. Loeb chose the latter substance as being the most likely pre- 

 cursor, and was supported by various investigators, notably Robertson, 

 who wanted the choline from the disintegrating lecithin for his choline 

 surface-tension theory of cell-division. However, the first investiga- 

 tions which were made did not lead to favourable results, for Masing, 

 taking the eggs of Arbacia pustulosa, applied the methods of Plimmer 

 & Scott to unfertilised eggs and morulae. Of the unfertilised eggs 



1 The eggs of another parasitic worm (the trematode, Distomum cygnoides) are said by 

 Schmidt to contain considerable amounts of esterified cholesterol. 



