ACTION OF THE SPERMATOZOON UPON THE EGG 235 



Finally, the rate of segmentation is the same in the eggs 

 developing parthenogenetically as in eggs fertilized by sperm. 

 This also proves that the sperm does not induce development 

 by any catalytic influence, but by the removal of an obstacle 

 or an inhibiting factor which obviously exists in the condition 

 of the cortical layer. Formerly the writer had suggested that 

 the removal of this obstacle consisted in the secretion of an 

 inhibitive substance from the egg, 1 a view which Bataillon 2 

 and Lillie 3 have since adopted; but the fact that complete 

 cytolysis of the unfertilized sea-urchin egg by saponin raises 

 the rate of oxidations in the same way as membrane formation 

 or fertilization suggests that the cytolysis of the cortical layer 

 is the essential removal of the " obstacle." 4 



The destruction of this cortical layer, the artificial membrane 

 formation, leads to a rapid increase in the rate of oxidations 

 in the egg of the sea-urchin. These oxidations form the foun- 

 dation of all the further cytological changes in the egg, since 

 their suppression inhibits these cytological changes. It is, 

 therefore, obvious that the point which demands further ex- 

 planation is the connection between membrane formation or 

 cytolysis and rate of oxidation. It is conceivable that the cor- 

 tical layer of the unfertilized egg forms a crust impermeable 

 to oxygen, but there is no proof for such an assumption. It 

 is also conceivable that there is present in the surface of the 

 egg a substance which inhibits the development of the egg, and 

 that this substance is altered or removed in the process of 

 membrane formation. It is finally conceivable that the surface 



1 Loeb, University of California Publications, Physiology, II, 1905. 



-Bataillon, "Le probleme de la fecondation circonscrit par I'impregnation 

 sans amphionyxie et la parthenogenese traumatique," Arch, de Zool. exper. et 

 urn., XLVI, 101, 1910. 



3 F. Lillie, Jour. Morphol, XXII, 361, 1911. 



4 There is a possibility that the egg contains in the cortical layer a catalyzer 

 or substances causing an increase in the rate of chemical reactions in the egg. 

 While in the unfertilized eggs these substances are not able to act, they are rendered 

 available if the cortical layer is cytolyzed. This possibility was set forth by me in 

 Proc. Soc. for Exper. Biol. and Med., VII, No. 4, April 20, 1910. 



