THE FERTILISATION OF THE ECxG 



19 



mediately form fertilisation membranes. After 15-20 minutes 

 they are then brought, for a period of 30-60 minutes, into sea 

 water made hypertonic by the addition of sodium chloride. 

 Finally they are returned to normal sea water. Many of the 

 eggs then cleave, and develop into normal larvae. 



In the eggs of the frog satisfactory results are obtained with 

 a treatment discovered by Bataillon (1910-1913). When punctur- 

 ed with a fine needle, such eggs extrude their perivitelline fluid, 

 and develop a fertilisation membrane. Cleavage, however, occurs 

 only if the eggs have previously been moistened with blood. It 

 appears that, for normal development to occur, a live blood 

 corpuscule, containing a nucleus, must be brought into the egg. 

 In this way, cleavage can be provoked in great numbers of eggs, 

 and in a certain percentage of the cases normal further de- 

 velopment will take place. A number of parthenogenetic larvae 

 have even been raised successfully through metamorphosis. 



The experiments on artificial parthenogenesis have provided 

 the opportunity for a further analysis of the processes that 

 initiate development. Two components of this phenomenon can 

 now be separated experimentally, which in normal fertilisation 

 are so interwoven that they can hardly be distinguished. For 

 instance, sea urchin eggs 

 have been treated with bu- 

 tyric acid, as in the first part 

 of Loeb's method, but then 

 kept in normal sea water. 

 When such eggs are brought 

 back into normal sea water, 

 the cortical reaction takes 

 place, with the result that 

 the fertilisation membrane is 

 elevated. However, cleavage 

 and further development fail 

 to occur. After some time, 

 the egg nucleus swells, its 

 nuclear membrane disap- f'^- ^- Activated egg of a star- 

 , . , fish. Egg nucleus in monaster. No 



pears, and a single aster ap- fertilisation membrane has been 

 pears in the surrounding formed in this case. After Dalcq. 



