Gametogenesis, Fertilization and Parthenogenesis 



203 



solution alone is effective. Also, Whitaker's 

 C'33) demonstration that activation could 

 occur with a decrease in respiratory rate re- 

 moved any general validity from that aspect 

 of Loeb's theory that involved the stimula- 

 tion of oxidative processes. No newer investi- 

 gations offer support for Loeb's views or any 

 recognizable modification thereof. 



R. S. Lillie ('41) proposed what may be 

 termed a bimolecular theory of activation 

 in which it is assumed that an activating 

 substance (A) is formed from the union of 

 two substances (B and S) that may be in- 

 itially present in low concentration in the 

 egg. Substance B is considered to be a prod- 

 uct of hydrolytic processes in the egg and 

 its formation to be stimulated by the action 

 of such agents as acids and heat, which can 

 act under anaerobic conditions. Substance S 

 is considered to be formed from synthetic 

 processes that may be stimulated by agents 

 such as hypertonicity acting only in aerobic 

 conditions. Since some of each is initially 

 present the threshold concentration of A can 

 be reached by increase in either B or S. This 

 theory provides a consistent formal interpre- 

 tation of a great mass of data that Lillie has 

 accumulated, mainly on starfish eggs. Thus 

 it accounts for additive and for sensitizing 

 effects when such agents as heat, acids, 

 hypertonicity and anaerobiosis are employed 

 in various combinations. In its general form 

 it is consistent, too, with other views, such as 

 the proposal that release of calcium is an 

 important factor in activation. 



The significance of calcium in activation 

 has been emphasized in two rather inde- 

 pendently developed theories, namely the 

 "sensitization to calcium" theory of Dalcq, 

 Pasteels and Brachet ('36; see also Brachet, 

 '47; Pasteels, '38a,b, '41; Pasteels and Fautrez, 

 '47) and the "calcivim release-protoplasmic 

 clotting" theory of Heilbrunn ('30-43). 

 These are based on experiments showing that 

 isotonic calcium chloride solutions or cal- 

 cium-rich solutions are effective activators 

 in many species of animals, that activation 

 by other agents is dependent upon the pres- 

 ence of calcium, and that depriving eggs 

 of calcium will sensitize them to the subse- 

 quent action of calcium solutions. Further 

 support for the general view may be found 

 in experiments by Scheer and Scheer ('47) 

 and by Runnstrom and Monne ('45a, b). 

 Heilbrunn's theory was developed for the 

 phenomenon of stimulation of cells in gen- 

 eral. In somewhat specific form it proposes 

 that the stimulating agent releases calcium, 

 from a calcium proteinate in the cell cortex, 



and the free calcium initiates a protoplasmic 

 clotting somewhat like blood clotting. It is 

 of interest in this connection that the fertili- 

 zin-antifertilizin interaction has been shown 

 to be largely dependent upon the presence 

 of calcium (Loeb, '13; Vasseur, '49) and that 

 fertilizin possesses some heparin-like activity 

 (Immers, '49). However, there is, as yet, no 

 direct evidence indicating that fertilizin is 

 concerned in the activation steps in the 

 processes of fertilization. There seems to be 

 no question that calcium is intimately in- 

 volved in the activation process and one 

 might speculate on its role on the basis of 

 its action on various enz5mies, such as 

 ATPase. However, the details of the picture 

 are still vague. There are very likely a large 

 number of substances concerned in the initial 

 changes of activation and it is not known 

 which constitute the primary reactants or 

 whether activation might be initiated by 

 various pathways. 



While the discovery of artificial partheno- 

 genesis did not bring the realization of the 

 early hopes that problems of fertilization 

 would be readily solved, it has provided im- 

 portant information concerning various as- 

 pects of the problem. It has, also, greatly 

 enlarged the scope of the attack on the prob- 

 lem of activation by substituting relatively 

 simple chemical and physical agents for the 

 spermatozoon. Further, since activation of 

 the egg involves changes in the activity of 

 various enzyme systems, artificial partheno- 

 genesis may come to be a useful tool for the 

 general problem of the factors responsible 

 for regulation of the enzymatic activities of 

 cells. 



REFERENCES 



Abelson, P. H. 1947 Permeability of eggs of 

 Arbacia punctulata to radioactive phosphorus. 

 Biol. Bull., ^3.-203. 



1948 Studies of the chemical form of P32 



after entry into the Arbacia egg. Biol. Bull., 95: 

 262. 



Aboim, A. N. 1945 Developpement embryon- 

 naire et post-embryonnaire des gonades normales 

 et agametiques de Drosophila melanogaster. Rev. 

 Suisse Zool., 52.-53-154. 



Allen, B. M. 1907 An important period in the 

 history of the sex-cells of Rana pipiens. Anat. 

 Anz., 3/.-339-347. 



Ball, E. G., and Meyerhof, B. 1940 On the occur- 

 rence of iron-porphyrin compounds and succinic 

 dehydrogenase in marine organisms possessing 

 the copper blood pigment hemocyanin. J. Biol. 

 Chem., y3^.-483-493. 



Ballentine, R. 1940 Analysis of the changes in 

 respiratory activity accompanying the fertiliza- 



