FERTILIZATION IN PLATYNEREIS MEGALOPS. IO9 



Mathews' experiments ('01) on Asterias may in this connection 

 be cited. He found that when the eggs of this starfish were got 

 while still in the germinal vesicle stage shaking would produce 

 development only after the eggs had remained in sea-water until 

 maturation was gone through with. Sea-water acts as a first 

 stimulus and mechanical shock induces further development. 

 So R. S. Lillie ('08) on the same egg finds that its responsiveness 

 to momentary elevation of temperature as a means of producing 

 artificial parthenogenesis "varies greatly at different periods in the 

 life of the egg.'' "The most favorable period is some little time 

 (10 to 20 minutes) before the separation of the first polar body." 



Reasoning thus, I thought that I might carry Platynereis eggs 

 through maturation with one agent and then through cleavage 

 with another. Eggs were, therefore, treated with KCl, KOH, and 

 NaOH in sea-water for various lengths of time and then subjected 

 to heat, shaking, and centrifugal force. In no case did I procure 

 cleavage although the first agent in each case caused maturation. 

 With Nereis, on the other hand, KCl and subsequent warming in 

 sea-water induces development (see Just '15b). 



It is interesting to note that eggs subjected to heat in the 

 minute quantities of sea-water that permit fertilization do not 

 develop beyond maturation. Apparently, the conditions for 

 successful artificial initiation of development are more exacting 

 than those for successful insemination. 



We may conclude, then, that the results of attempted cross 

 fertilization and artificial parthenogenesis are harmonious with 

 those of sea -water insemination, so far as cleavage is concerned, 

 in their negative results. The fundamental questions are : (i) the 

 significance of the sea-water insemination and (2) the extent to 

 which the results with Nereis sperm and with parthenogenetic 

 agents are capable of like interpretation. 



Discussion. 



Any analysis of fertilization must deal with the phenomena 

 from the point of view of heredity or of initiation of development. 

 Considered as the .process of initiating development, fertilization 

 may be divided into the stages of insemination, sperm pene- 

 tration, and germ nuclei copulation. As Lillie has repeatedly 



