92 EXTERNAL FACTORS III. 3 



completely by a furrow. When segmentation occurred the first 

 two blastomeres were unequal and detached ; the vegetative 

 hemisphere was hardly segmented at all in later stages, the 

 previous divisions having disappeared. The nuclei were affected 

 in various ways, and the directions of the cleavage spindles 

 altered. The capacity for resistance to these evil effects was 

 noticed to increase as development advanced. 



The polar area produced in these experiments recalls the polar 

 areas observed by Roux in Frogs' eggs exposed to a horizontal cur- 

 rent, at right angles, therefore, to the axis. Alternating currents 

 of 50 and 100 volts were employed. The eggs were fertilized 

 two or three hours before the commencement of the experiment. 

 In from fifteen to thirty seconds after exposure two polar 

 areas appeared in each egg. The polar areas were turned 

 towards the electrodes. They were marked, dotted in various 

 ways, and flecked with white extruded drops of yolk, and 

 separated by furrows from a middle or ' equatorial ' zone, the 

 width of which varied directly with the distance of the egg 

 from the electrode, inversely with the strength of the current 

 and the duration of exposure. 



Unfertilized ova were found to react in the same way. So 

 also eggs in which segmentation had begun, and in those cases 

 where the furrow cut the equatorial zone obliquely, the two 

 halves of the latter turned away from one another. 



The polar areas appear too in eggs which are exposed in the 

 ' morula ' stage, each cell having in addition a polar area of its 

 own. The latter, however, do not appear in enfeebled eggs, but 

 only the former. 



In the gastrula and later stages the reaction occurs, but less 

 markedly. 



None of the eggs which have been exposed to the current 

 develops any further. They stick to the jelly, and consequently 

 lose their power of rotation. 



Similar results were obtained by the use of the continuous 

 current (43 volts), but the anodic and the kathodic areas usually 

 differed from one another in certain details. 



It is important to notice that neither in these experiments, 

 nor in another in which the eggs were placed inside a glass 



