6. How can an alteration of the surface of the egg--_e. g._, a cytolytic or other destruction of the cortical layer--lead to a beginning of development? The answer is possibly given in the relation of oxidation to development. The writer found in 1895 that if oxygen is withdrawn from the fertilized sea-urchin egg it can not segment and this seems to be the case for eggs in general.[103] In 1906 he found that the rapid disintegration of the eggs of the sea urchin which follows artificial membrane formation could be prevented when the eggs were deprived of oxygen or when the oxidations were suppressed in the eggs by KCN. This suggested a connection between the disintegration of the egg after artificial membrane formation and the increase in the rate of oxidations; and he found further that the formation of acid is greater in the fertilized than in the unfertilized egg. He, therefore, expressed the view in 1906 that the essential feature (or possibly one of the essential features) of the process of fertilization was the increase of the rate of oxidations in the egg and that this increase was caused by the membrane formation alone.[104] These conclusions have been since amply confirmed by the measurements of O. Warburg as well as those of Loeb and Wasteneys, both showing that the entrance of the spermatozoön into the egg raises the rate of oxidations from 400 to 600 per cent., and that membrane formation alone brings about an increase of similar magnitude. Loeb and Wasteneys found that the hypertonic solution does not increase the rate of oxidations in a fertilized egg. It does do so, however, in an unfertilized egg without membrane formation, but merely for the reason that in such an egg the hypertonic solution brings about the cytolytic change in the cortex of the egg underlying membrane formation.[105] According to Warburg it is probable that the oxidations occur mainly if not exclusively at the surface of the egg since NaOH, which does not diffuse into the egg, raises the rate of oxidations more than NH₄OH which does diffuse into the egg. And finally, the same author showed that the oxidations in the sea-urchin egg are due to a catalytic process in which iron acts as a catalyzer.[106] In view of all these facts and their harmony with the methods of artificial parthenogenesis the suggestion is justifiable that the alteration or cytolysis of the cortical layer of the egg is in some way connected with the increased rate of oxidations. [103] The writer found that the eggs of _Fundulus_ will segment a number of times even if all the oxygen has apparently been removed. [104] Loeb, J., _Biochem. Ztschr._, 1906, ii., 183. [105] Thus the treatment of an unfertilized egg without membrane with a hypertonic solution combines two effects, first the general cytolytic alteration of the cortical layer of the membrane and the corrective effect of the hypertonic solution. The former effect raises the rate of oxidations in the egg, the latter does not.