x] CAUSE OF DEVELOPMENT 143 



but unless some corrective process is applied, the cytolytic 

 action continues and leads to the final disintegration of the 

 egg. In the improved method for bringing about artificial 

 parthenogenesis the function of the hypertonic solution is 

 to have this corrective effect; its exact mode of action is 

 unknown, but it seems to induce the formation within the 

 egg of some substance which counteracts the later cytolytic 

 effect of the butyric or other acid. 



The cytolytic effect of the agents which induce artificial 

 parthenogenesis can also be counteracted by depriving the 

 eggs of oxygen after treatment with the butyric acid or 

 other agent. Absence of oxygen completely inhibits cell- 

 division, but if the eggs are placed in normal sea-water after 

 being deprived of oxygen for some hours, they begin to 

 segment in the typical manner instead of undergoing cyto- 

 lysis. This might suggest that the effect of the hypertonic 

 solution is to prevent the absorption of oxygen, but that 

 this is not a full explanation is shown by the fact that the 

 hypertonic solution must contain oxygen if it is to be suc- 

 cessful. The actual formation of the membrane can take 

 place in the absence of oxygen, but it seems that a result of 

 the processes which lead to its production is greatly to 

 increase the oxygen absorption of the egg, and this leads 

 to cytolysis. If the egg is kept without oxygen for some 

 hours, or treated with a hypertonic solution, other processes 

 take place in the egg which regulate the oxygen absorption 

 when the egg is replaced in sea-water, and allow normal 

 development to occur. When development is brought about 

 by treatment with a hypertonic solution alone, it must be 

 supposed that this acts in a double capacity; it tends to 

 cause cytolysis and thus to initiate development, but at 

 the same time it corrects the excessive cytolytic effect, and 

 allows development to proceed. 



