462 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



The increase in oxygen-consumption is obviously much less than 

 that caused by membrane-formation and it is, moreover, transitory, 

 falling off with time after the exposure instead of increasing, as it does 

 when the eggs are normally fertilized or treated with butyric acid. 

 On the other hand in eggs in which membrane-formation has been 

 induced by butyric acid or by the entry of a spermatozoon, no increase 

 whatever and no important decrease in the rate of oxidations could 

 be observed on treatment with hypertonic sea-water. The corrective 

 effect of hypertonic solutions in preventing the death and disintegra- 

 tion of the eggs which succeeds membrane-formation by cytolytic 

 agents is therefore not to be sought in an effect upon oxidations. It 

 may possibly reside in an effect upon underlying hydrolyses, for these, 

 as we have seen, will bring about the destruction of the egg if they are 

 permitted to go forward while the oxidations are retarded or prevented 

 by lack of oxygen or by cyanides, and hence if they were dispropor- 

 tionately rapid, even in eggs in which oxidation were proceeding they 

 might be presumed to exert a like deleterious effect. However this 

 may be, the action of the hypertonic solutions upon the egg is not 

 reversible upon restoration to normal sea-water. The effect is to induce 

 a permanent alteration of the egg which renders it able to withstand 

 partial cytolysis (membrane-formation) without injury. Thus Loeb has 

 shown that if the unfertilized eggs of Strongylocentrotus purpuratus be 

 placed for from two to two and a half hours in hypertonic sea-water 

 (50 c.c. sea-water + 8 c.c. 2| m. Ringer solution) they may be returned 

 to normal sea-water and subsequent treatment with butyric acid, even 

 forty-eight hours later, will induce, not merely membrane-formation, 

 but full and normal development of the embryo. 



THE RELATIONSHIP OF PHOSPHOLIPINS TO THE SYNTHESIS OF 



NUCLEAR MATERIAL AND THE EFFECTS OF LECITHIN 



UPON EARLY DEVELOPMENT. 



The leading results of the early development of the embryo are, 

 in the first place, the very great increase of cellular surface due to 

 repeated subdivisions of the original egg-cell and in the second place 

 an increase in the proportion of nuclear to cytoplasmic constituents. 

 The earlier estimations of Boveri led him to the conclusion that the 

 mass of nuclear material in the cells is doubled at each cell-division, 

 but the more recent estimations of Conklin have tended to greatly 

 reduce this estimate, the average nuclear growth during cleavage 

 amounting, it appears, to not more than from five to nine per cent, for 

 each cleavage that occurs. Nevertheless there is a definite increase 

 in nuclear material during the formation of the multitude of new cells 

 which comprises the Blastula-stage of the sea-urchin and since during 

 this period of development no growth of cytoplasm occurs, the cyto- 

 plasm of the new cells occupying collectively the same space as the 

 original egg-cell, it is evident that a disproportion of nuclear to cyto- 



