Vol. XXVIII. May, 1915. No. 5. 



BIOLOGICAL BULLETIN 



ON THE RHYTHMICAL SUSCEPTIBILITY OF DE- 

 VELOPING SEA URCHIN EGGS TO /«9' 

 HYPERTONIC SEA WATER. 



ARTHUR RUSSELL MOORE. 



(From the Biological Laboratory of Bryn Mawr College and the Marine Biological 

 Laboratory at Woods Hole.) 



In a recent communication M. Herlant^ attempting an 

 analysis of Loeb's method of artificial parthenogenesis concludes 

 that (i) the fatty acid treatment gives rise to the rhythmical 

 activity of the centrosome but never to normal divisions of the 

 egg; (2) the treatment of the eggs with hypertonic sea water 

 causes the formation of accessory asters and is necessary to 

 complete the causes for normal division ; (3) the optimum results 

 are obtained by applying the hypertonic solutions at certain 

 intervals after fatty acid treatment, viz., 30 and 70 minutes and 

 possibly 1 15-120 minutes, while with 40-50 and 95-100 minute 

 intervals marked minima are shown. 



As to the first generalization, Herlant ignores the fact that 

 in Strongylocentrotus and Arhacia the fatty acid treatment alone 

 may cause normal segmentation. If the eggs of S. purpuratus 

 are kept at a low temperature (5°-io°) after acid treatment 

 alone, they divide regularly and may reach the morula stage.^ 

 In Arhacia eggs, normal segmentation may take place after 

 acid treatment without subsequent treatment with the hyper- 

 tonic solution, but does not as a rule proceed beyond the two- 

 cell stage. On the other hand hypertonic treatment alone may 

 cause Arhacia eggs to segment and develop into swimming larvse, 

 while it brings about only early segmentation stages in the eggs 

 of Strongylocentrotus. 



1 M. Herlant, Comptes Rendus de I'Academie, T. 158, p. 1531. 

 ^ J. Loeb, "Artificial Parthenogenesis and Fertilization," p. 76. 



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