On Phosphorus Metabolism in Embryonic Life

ABSTRACT An investigation was made of the phosphorus metabolism of several marine invertebrate eggs (two echinoderms, one gephyrean annelid, and two Crustacea). The distribution of phosphorus-containing compounds was measured before and after development had taken, place. Data are given for the total and lipoid phosphorus, the total water-soluble and stable organic water-soluble phosphorus, the inorganic ortho-and pyro-phosphate, the phosphoprotein and the nucleoprotein. During the development of the sand-crab (Emerita analoga) water is absorbed from the environment, as in the well-known cases of the frog, the trout, and various cladocerans. The egg shell of the brine-shrimp (Artemia salina) contain both calcium and haematin, offering thus a parallel with the shell of avian eggs. During the development of the sanddollar egg (Dendraster excentricus) there is an increase in total phosphorus per unit weight of dry solid. It is pointed out that this absorption of an element from the sea water by the embryo must be taken into account in considering the penetration of marine organisms into fresh water, if, as seems probable, the phosphorus concentration in an aqueous environment may act as a limiting factor. The spicules of the sanddollar pluteus probably contain inorganic phosphate, in quantity roughly corresponding to the amount taken in by the developing egg from the sea water. In all cases so far studied the extent to which lipoid phosphorus is transformed into other forms of phosphorus during embryonic life is proportional to the amount of lipoid phosphorus present at the time of fertilisation. Included in the large stores found in certain eggs there is a fundamental quota which no egg can do without, though this may be, reckoned in absolute values, very small. A computation shows that the contribution of one echinoderm spermatozoon to one egg is of the order of a ten-thousandth part of the phosphorus which is there already. The analyses reported in this paper indicate that, in spite of the large increase of visible nuclear matter during echinoderm development, there is no corresponding synthesis of nuclein. The formation of the chromatin of the nuclei must therefore consist in an organisation of preformed nucleic acids into structural arrangement and not in a manufacture of these compounds by chemical means from other raw materials. Nuclein synthesis, however, certainly occurs in some eggs, and study of the relevant investigations of other workers leads to the conclusion that it is associated with uricotelic metabolism, terrestrial development, and the properties of cleidoic embryos. Wherever the purine ring is synthesised by embryonic cells for nitrogen excretion, there a notable synthesis of the purine ring for cell-nuclei is also found : whatever this is not so, there the eggs are provided by the parent organism with sufficient nuclein for the needs of the embryos.