Gametogenesis, Fertilization and Parthenogenesis 



197 



ported by Ruffo and Monroy ('45) for egg 

 brei. 



Changes in Permeability. In addition to the 

 early demonstration that fertilization results 

 in an increased permeability to water (R. 

 S. Lillie, '16) and such nonelectrolytes as 

 ethylene glycol (Stewart and Jacobs, '32), 

 recent tracer experiments (Abelson, '47; 

 Brooks and Chambers, '48; Lindberg, '48) 

 show a great increase in permeability to 

 phosphate. The fate of the phosphate that 

 is incorporated into the fertilized egg will 

 be discussed further below. 



Changes in Electrical Properties. Activation 

 of eggs has often been considered analogous 

 to stimulation of nerves. However, attempts 

 (Peterfi and Rothschild, '35; Rothschild, '38, 

 '46) to detect the propagation of an action 

 potential over the egg surface upon fertiliza- 

 tion in sea urchins and frogs have been un- 

 successful. In fact, no potential difference 

 was found across the surface of the sea 

 urchin egg. While this might be attributable 

 to short-circuiting between the electrodes, the 

 fact that eggs can be fertilized after insertion 

 of the electrode indicates that the fertiliza- 

 tion reaction does not depend upon there be- 

 ing a potential difference across the egg 

 surface. Also, the membrane resistance is ap- 

 parently unchanged upon fertilization in sea 

 urchins and frogs (Cole, '35; Cole and Spen- 

 cer, '38; Cole and Guttman, '42). Membrane 

 capacitance is approximately doubled upon 

 fertilization in sea urchins, indicative of 

 change in dielectric constant, but no change 

 is obtained in eggs of Cumingia, Chaetopterus 

 or the frog (Cole and Cvirtis, '38; Cole and 

 Guttman, '42). 



Changes in MetaboHsm. Detailed surveys 

 of the metabolic changes that occur upon 

 fertilization have been presented by Need- 

 ham C42) and Brachet ('47). The newer 

 ovitlook in this field is largely due to the 

 work of Whitaker ('31a,b,c, '33a,b), who 

 refuted the idea that fertilization was in- 

 variably accompanied by a rapid rise in rate 

 of oxidation. In fact a decrease was found to 

 occur in some species, such as the annelid 

 Chaetopterus and the mollusk Cumingia, 

 while in other animals such as the starfish 

 and the annelid Nereis there is no very 

 marked change. In a single species of animal, 

 too, there may be an increase, decrease or 

 no change depending upon the condition of 

 the unfertilized egg^ as Tyler and Humason 

 ('37) have shown in Urechis. Even in sea 

 urchins, the classic rise, first described by 

 Warburg ('08), does not occur if the eggs 

 are fertilized very soon after removal from 



the ovary, since, as Borei ('48, '49) has 

 shown, the freshly shed unfertilized egg 

 has a respiratory rate as high as that of the 

 fertilized egg. Theories of activation that 

 are dependent upon an increased rate of 

 oxidation are evidently no longer tenable. 



It has also been held that the oxidative 

 processes differ qualitatively in the fertilized 

 and imfertilized egg. For example, Ruben- 

 stein and Gerard ('34) and Korr ('37) have 

 reported large differences in the temperature 

 coefficient of the rate of oxygen uptake of 

 fertilized and unfertilized eggs of sea 

 urchins. On the other hand, Tyler and Huma- 

 son ('37) found no significant differences in 

 sea urchins and other species of animals, and 

 Borei and Lybing ('49) confirm this with 

 sea urchins. This is consistent, too, with the 

 newer findings concerning sensitivity to 

 cyanide and carbon monoxide. Runnstrom 

 ('28, '30a) and Korr ('37) had reported 

 that these agents do not inhibit the respira- 

 tion of unfertilized sea urchin eggs. Along 

 with the initial failure of many investigators 

 to detect cytochrome spectroscopically in sea 

 urchin eggs, this led to the view (Korr, '37) 

 that before fertilization the respiration is 

 mediated by a nonferrous autoxidizable fer- 

 ment, such as a flavoprotein, while upon fer- 

 tilization the previously unavailable cyto- 

 chrome is thrown into circulation. However, 

 Robbie ('46) has shown that if precautions 

 are taken to avoid absorption of the hydrogen 

 cyanide by the alkali well of the respiration 

 vessel, the oxygen uptake of the unfertilized 

 egg can be almost completely inhibited. 

 Also, photo-reversible inhibition of oxygen 

 uptake by carbon monoxide has now been 

 demonstrated by Rothschild ('49a), who ac- 

 counts for the earlier misinterpretations on 

 the basis of a simultaneously occurring light- 

 inhibition of respiration and stimulation of 

 oxygen uptake by carbon monoxide (prob- 

 ably by oxidation of the carbon monoxide). 

 On the basis of these experiments, the demon- 

 stration of the presence of a cytochrome 

 oxidase (Krahl et al., '41) and the spectro- 

 scopic identification of cytochromes (Roths- 

 child, '49a), it may now be concluded that 

 respiration is mediated by the cytochrome 

 system before as well as after fertilization. 



In regard to the dehydrogenase part of the 

 respiratory system Runnstrom ('30a) and 

 Orstrom ('32) found no change in rate of 

 methylene blue reduction upon fertilization 

 in sea urchins, whereas Ballentine ('40), 

 using ferricyanide as the electron acceptor, 

 found an increase. This contradiction still 

 needs to be resolved. Concerning the path- 



