PERIODS OF SUSCEPTIBILITY IN THE DIFFEREN- 

 TIATION OF UNFERTILIZED EGGS 

 OF AMPHITRITE. 



J. W. SCOTT. 



While studying the unfertilized egg of Amphitrite at the Ma- 

 rine Biological Laboratory, Wood's Holl, Mass., I verified Fisch- 

 er's 1 result that the eggs could be caused to develop cilia by 

 squirting them from a pipette, by transferring them from one dish 

 to another, or by some other sort of mechanical agitation. I be- 

 lieve however that it is inadmissible to speak of this development 

 as parthenogenesis, meaning the production of a normal embryo 

 from an unfertilized egg. Ciliated, swimming structures result, 

 but their differentiation takes place with only partial or abnormal 

 and usually without any definite segmentation. I will discuss 

 the morphology of these processes in another paper. Lillie 2 has 

 shown clearly a similar differentiation in the Ch&topterus egg. 



In addition to Fischer's results, I found : (i) At least two criti- 

 cal periods in which the egg is highly susceptible to mechanical 

 stimulation, one period thirty to forty-five minutes, the other 

 eighty to one hundred minutes after they are removed from the 

 body and placed in sea-water ; (2) slight agitation is more effec- 

 tive in the second period than in the first ; rougher handling is 

 better in the first than in the second in which the eggs are more 

 easily broken into fragments. (3) Frequent and moderate 

 squirting after thirty to fifty minutes seems more effective than 

 one hard squirting after the same time. 



In my early experiments with certain salt solutions, the results 

 were sometimes discrepant, and there was great variableness in 

 the number of swimming eggs obtained under apparently identi- 

 cal conditions. About this time Fischer's paper came into my 

 hands. He had shown that " parthenogenetic development can 

 be produced by adding a small amount of Ca-salt to sea-water " 



1 Fischer, Martin H., Am. Jour. Phys., 1902, III., p. 301. 



2 Lillie, F. R., Archiv fur Entwickelungstriechanik der Organismen, 1902, XIV., 



P- 377- 



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