Vol. XXIX. September, 1915. No. j 



BIOLOGICAL BULLETIN 



STUDIES IN ARTIFICIAL PARTHENOGENESIS. 

 II. PHYSICAL CHANGES IN THE EGG OF ARBACIA. 



L. V. HEILBRUNN. 



CONTENTS. 



I. Physical Organization of the Egg 149 



II. Cortical Changes 158 



A. Membrane Elevation and Membrane Swelling 158 



B. Permeability Changes in the Vitelline Membrane 160 



C. Theories of Membrane Elevation 163 



D. Cortical Action of Heat and of Various Chemicals 169 



E. Inhibitors to Membrane Swelling 174 



F. Cortical Changes at Fertilization 178 



G. The Significance of Cortical Change 183 



III. Internal Changes. The Problem of Segmentation 184 



A. Theories of Segmentation 184 



B. The Action of Hypertonic Sea-water in the presence of KCN 185 



C. An Analysis of the Methods of Producing Segmentation in the 



Unfertilized Arbacia Egg 188 



IV. Summary 200 



V. References 201 



I. PHYSICAL ORGANIZATION OF THE EGG. 



In spite of the many researches on the sea-urchin egg very 

 little is known of its physical make-up. Year after year the 

 egg is used in attempts to analyze fundamental problems and 

 various theories have been based upon experiments with it. 

 And yet, but little is known definitely about the type of physical 

 organization which it possesses. Is the egg essentially fluid 

 or is it a more or less rigid jelly, is the unfertilized egg surrounded 

 by a microscopically visible membrane or by a hypothetical 

 film beyond the limits of vision, what indeed is the nature of 

 the membrane which controls osmotic interchange? These 



149 



