86 m/RVEY OF i\] iJirri'j/i/x'AT/ji^ 



The reproductive cells of starfish behave somewhat 

 differently (Barron, I.e.). Both unfertilized eggs and 

 sperm were dead after being deprived of oxygen for 4 

 hours (the species is not indicated). 



The fertilization of Arhacia eggs does not take place if 

 both eggs and sperm are kept under anoxic conditions. 

 When care is taken to eliminate every trace of oxygen 

 (Barron, I.e.) not even the stage of the elevation of the 

 fertilization membrane is reached, although this process 

 seems to require only minimal traces of oxygen (Har- 

 vey, I.e.). 



Under normal conditions the first response of the G^g 

 to insemination consists in the breakdown of a thin layer 

 of cortical granules. This phenomenon, known as the 

 cortical layer response, can be elicited under experimen- 

 tal conditions by a variety of stimuli (Moser, 1939). It 

 is indeed interesting that it takes place in unfertilized 

 Arhacia eggs maintained under rigid anaerobic conditions. 

 Kitching and Moser (1940) observed it when the eggs 

 were treated in the absence of oxygen with V^ per cent 

 saponin in sea water, with isotonic urea or sucrose so- 

 lutions, or when they were punctured with a micro- 

 needle. If unfertilized eggs of the sea-urchin were first 

 treated with urea and this substance was then removed 

 by repeated washings with sea water— strictly anoxic con- 

 ditions being maintained during all these manipulations 

 — the eggs began to undergo cleavage after oxygen was 

 admitted. Obviously, then, the stimulus that prepares 

 the eggs for cleavage does not require molecular oxygen. 



The cleavage process itself, on the other hand, is en- 

 tirely dependent on the presence of oxygen. It does not 

 take place in the complete absence of oxygen, neither at 

 very low tensions, e.g., below 4 mm. of mercury (Loeb, 

 1895 ; Harvey, 1927 ; Amberson, 1928 ; Tang and Gerard, 

 1932). The fact that the oxygen consumption of both 

 fertilized and unfertilized Arhaeia eggs is somewhat de- 



