CHAPTER IX 



EXPERIMENTS OF BORN AND OF ROIJX 



Pfluger, as we have seen, believes that when the frog's %g^ 

 is rotated so that the white hemisphere is turned uppermost, 

 no rotation of the contents of the egg takes phxce. Born 

 ('84, b) repeated this experiment of Pfliiger and sought, by 

 making actual sections of the eggs, to hnd out whether any 

 changes do take place in the interior of the reversed eo-o-.i 



Sections through normal, fertilized or unfertilized frogs' eggs 

 show that there is a peripheral, darkly pigmented rind in the 

 form of a shell thickest at the black pole (30 to 40 microns) 

 and fading away at the white pole (Fig. 8). Beneath the 

 black rind in the upper hemisphere lies a brownish pig- 

 mented protoplasm. In the centre of this and just under the 

 black pole is found in cross-section a clearer spot containing 

 the nucleus. The yolk lies within the white hemisphere. The 

 yolk appears coarsely granular, while the protoplasm in the 

 dark hemisphere is finely granular. 



Changes that take place in the Interior of the 

 Egg after Rotation 



Born observed in the living Qg<g that when the white hemi- 

 sphere is kept upward, it gradually becomes darker in color, 

 owing to the appearance of a grayish-white area. Pfliiger had 

 noticed the same phenomenon. This area grows larger in pro- 

 portion to the length of time that the ^^g has been turned. 



Examination of sections of an inverted ^gg shoAvs that fort}'- 



1 After the first account of Bora's had appeared, other papers dealing with 

 the same subject by Roux, Rauber, and 0. Hertwig were also published. These 

 authors all agree with Born. 



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