Artificial Parthenogenesis in Starfish Eggs 41 1 



The conditions of this change of susceptibihty are at present 

 unknown. I have endeavored to determine if a similar variabihty 

 exists in respect to fertilization by spermatozoa; and the result 

 has appeared that although normal fertilization is possible through- 

 out a far greater period in the history of the egg (namely, at any 

 time after maturation has begun until several hours after its 

 completion) a very similar variation in the degree of susceptibility 

 to the fertilizing influence does in fact exist. Conditions for fertili- 

 zation by spermatozoa are at their best during the maturation period, 

 at or about the time of separation of the first polar body; and later 

 they become less favorable. There is thus a certain parallehsm 

 between the conditions of artificial fertilization by momentary 

 warming and of normal fertilization by spermatozoa. The fol- 

 lowing table gives the results of two series of experiments. Sper- 

 matozoa were added to successive portions of eggs, taken in each 

 series from a single female, at the indicated intervals after removal 

 from the animal. The condition of the eggs at the time of fertili- 

 zation is indicated by the italicized portion in parentheses. 



Four other similar series of experiments were performed with, 

 in general, very similar results. In all of these the most favorable 

 time for fertilization was either before or about at the time of the 

 separation of the first polar body; eggs fertilized at periods of one 

 to three hours after the completion of maturation gave few or no 

 larvae, and these were mostly abnormal. These experiments 

 agree in indicating that the egg gives the best response to the 

 fertilizing influence of the spermatozoon at or near the time of 

 separation of the first polar body. After the separation of the 

 second polar body the proportion of developing eggs undergoes 

 rapid decline. It is however possible for eggs at such stages to 

 give normal larvae on fertilization, although the optimal conditions 

 are found at earlier stages. 



On comparison with the results of momentary warming a cer- 

 tain agreement is seen. The egg responds best to both fertilizing 

 influences at or near the time of separation of the first polar body 

 although rather before than after this event in the case of warming 

 This agreement is of some further interest as indicating that the 

 essential determining conditions of the initiation of the develop- 



