STUDY OF FERTILIZATION 431 



Since the initial phases of fertihzation and of artificial 

 parthenogenesis are alike, and since the subsequent phase of 

 development depends on the existence of a sperm-aster, is it 

 possible that the process of artificial parthenogenesis can only 

 be completed by treating the egg in such a way as to induce the 

 formation of a second aster ? 



As is well known, eggs which have been suljjected to ' mem- 

 brane formation ' will proceed to normal development if 

 treated with hypertonic sea-water. The recent work of Herlant 

 (16) shows clearly that such treatment does actually lead to 

 the formation of a second aster. Without such treatment 

 activated eggs behave in exactly the same way as eggs from 

 which spermatozoa have been removed after normal initial 

 activation. 



The formation of accessory asters within fertilized, or within 

 artificially activated eggs, when exposed to hypertonic sea- 

 water, is now quite well established (Herlant, 16 ; Vies and 

 Dragoiu, 29). Herlant has shown that one of these asters 

 comes into communication with the female aster and forms 

 a normal mitotic spindle in the case of artificially activated eggs ; 

 further, he has shown that the optimum conditions for accessory 

 aster formation and the optimum conditions for development are 

 exactly equivalent. When it is remembered that Morgan (26) 

 and Wilson (30) showed that similar treatment led to the 

 formation of asters within unfertilized eggs, it will be realized 

 that the work of Herlant has thrown much light on the 

 whole process of artificial parthenogenesis. We are now able 

 to give a reasonable explanation of the fact that membrane 

 formation may either precede or follow^ treatment with hyper- 

 tonic sea-water. There is no need to postulate the ' corrective 

 substance ' of Loeb. Since the egg is more permeable to water 

 after membrane formation than before, it is equally clear why 

 treatment with hypertonic sea-water is more rapidly effective 

 after membrane formation than before (Loeb). 



We can, therefore, summarize the process of artificial par- 

 thenogenesis as follows. There are two phases, (i) An activa- 

 tion of the egg, by the destruction of a lipoid film at the surface. 



H h 2 



