BIOCHEMISTRY OF THE SEXUAL ORGANS 315 



division sets in, and oxygen consumption and development are to a 

 large extent independent of each other. Development is therefore 

 not the cause of the increased oxygen consumption. On the con- 

 trary, the increased oxygen consumption is the cause of develop- 

 ment, and fertilisation is the method by which this increased oxygen 

 consumption is induced. This conception has received strong con- 

 firmation by the recent work of Shearer.^ On bringing together 

 the eggs and the sperm of Echinus microtuberculatus there is at once 

 during the first minute an enormous increase in the oxygen con- 

 sumption. In fact, this increase during the first minute is much 

 greater than that observed at any subsequent period. The significant 

 fact is that this increase occurs before the spermatozoa have pene- 

 trated the cell membrane. The increased oxygen consumption must 

 therefore be due to a change at the extreme periphery of the egg. 

 Shearer suggests that the cortical lipoid layer contains traces of 

 iron. As we have seen (see p. 313) traces of iron may act as a 

 catalyst: for instance, they greatly increase the oxygen absorption 

 by emulsions of lecithin.^ In the unfertilised egg the iron is present 

 in the cortical layer in an inactive condition, and is set free by the 

 alteration in the cortical layer induced by the spermatozoon. 



If the initial cytolysis is allowed to proceed unchecked the eggs, 

 although they begin to divide, eventually undergo complete cytolysis 

 and die. A second corrective process is necessary to save the life 

 of the cell. Experimentally this second corrective life-saving process 

 consists either in stopping oxidation altogether by immersing the 

 eggs in a potassium cyanide solution or by depriving them of oxygen, 

 or by placing the eggs for a short time in a hypertonic salt solution 

 containing oxygen. The eggs then develop in the same way as if 

 they had been fertilised by a spermatozoon. They develop into 

 larvae, and such larvae can, with the necessary care, be reared to 

 sexual maturity. Delage has succeeded in doing so in the case of 

 the sea-urchin. Loeb and Bancroft raised a parthenogenetic frog 

 through metamorphosis and found that its sex glands contained eggs. 



How this second process, which Loeb terms the "corrective 

 factor,'' operates is not very clear. One can only conclude that it 

 is not only necessary'that the metabolism of the mature ovum should 

 be stimulated and reach a certain optimum, but the processes thus 

 initiated by the formation of a fertilisation membrane must be 

 properly co-ordinated. Otherwise the entire developmental process 

 may go astray. 



If it be admitted that artificial parthenogenesis reproduces the 



1 Shearer, " On the Oxidation Processes of the Echinoderm Egg during 

 Fertilisation," Proc. Roy. Soc, B., vol. xciii., 1921. See above, pp. 186-197. 



2 Thunberg, loc. cit. See also Warburg and Meyerhof, Zeitseh. f. physiol. 

 Chem., 1913, vol. Ixxxv. 



