FERTILISATION 185 



lanthaaum nitrate, cause an enormous rise in resistance, when used 

 in solutions of 0-0005 Molar strength. Harvey ^ has adduced a 

 considerable body of evidence for believing that the egg becomes 

 more permeable to alkalis during fertilisation. E. S. Lillie^ has 

 also shown that Ariacia eggs take several times more water after 

 fertilisation than before. 



Brachet^ has given a very full analysis of the conditions 

 governing polyspermy in Amphibians. The controlling factor would 

 seem to be the aster and centrosome. Once the egg-aster has formed, 

 no extra spermatozoa can enter the egg under normal conditions, and 

 even in those eggs in which polyspermy has been induced by treat- 

 ment of the egg by chemical agents, or the use of very concentrated 

 sperm emulsions, it is found that one sperm never penetrates the 

 region of the astral rays of another sperm head. Artificial aster 

 formation, however, can be brought about in the ripe Echinoderm egg 

 by placing the egg in hypertonic sea-water. Harlent * has advanced 

 strong evidence in a recent paper to prove that this is the r61e of 

 hypertonic solutions in the various methods of producing artificial 

 parthenogenesis in these animals, such as those of Loeb. Loeb found 

 that preliminary treatment of the egg in weak solutions of a fatty 

 acid, such as butyric, was insufficient alone to induce development ; 

 subsequent treatment in hypertonic sea-water for a few minutes was 

 also necessary. Loeb considers that the oxidation processes set up 

 in the ovum by the initial treatment with butyric acid go too far 

 unless controlled by the second treatment. This, he believed, was 

 accomplished by the hypertonic sea- water. Warburg ^ and Meyerhof ,•* 

 however, have shown that a greatly increased consumption of oxygen 

 takes place when the eggs are placed in hypertonic sea- water. It is 

 probable, therefore, that hypertonic sea-water helps to initiate 

 parthenogenetic development on account of the aster formation it 

 produces in the cytoplasm of the ovum, which renders subsequent 

 segmentation possible. Additional evidence on this point has been 

 brought forward by Vl^s and Dragoin,^ who have shown that when 

 the dividing egg is subjected to increased pressure normal aster 



' Harvey (N.), "The Permeability and Cytolysis of Eggs," Science, N.S., 

 vol. xxxii., 1910. 



^ Lillie (E. S.), " Increase of Permeability to Water following Normal and 

 Artificial Activation of the Sea-Urchin Eggs," Amer. Jour, of Physiol., vol. xl., 

 1916. 



^.Brachet (A.), L'muf etles Facteurs de VOntogenese, Paris, 1917. 



* Harlent, "Comment agit la solution hypertonique dans la parth^no- 

 g6nfese exp6rimentalle," Arch. d. Zool. Exp., vol. Ivii., 1918. 



* Warburg, "Uber die Oxydationen in lebenden Zellen,'' Arch. f. ges. 

 Physiol., vol. Ixvi., 1910. 



^ Meyerhof, " Untersuchungen fiber die Warmetonung der vitalen 

 Oxydationsvorgange in Biern," Biochem. Zeitsch., vol. xxxv., 1911. 



'' Vlfes and Dragoin, " Etudes sur la pression osmotique d'arr^t de la 

 division oellulaire," Arch. d. Biol., vol. xxxi., 1921. 



