AMBLYSTOMA rUNGTATUM. 5 



"All the observers of the pigmentecl, developing Batrachian egg 

 agree in this, that sometime after fertilization they turn themselves 

 always with the dark pole upward, even if it was not the case at 

 first. A sufficient reason for this cannot be found. According to 

 my view, this turning of the yolk is ap|>arent, wiiether general or 

 in part, since only the pigmentary layer following the influence of 

 the newly determined pole, displaces itself."* 



Segmentation commences by the appearance of a furrow on the 

 dariv hemisphere which stretches around the egg, the two ends 

 meeting at the light j)ole, and thus dividing the egg into two 

 hemispheres, each of which contains half of the dark and half of 

 the light hemispheres. The two color areas during the early stages 

 of segmentation are more distinctly outlined than at any other 

 period. The dark area has become a rich dark brown. The 

 second furrow forms a great circle at right-angles to the first, and 

 starts also at the dark pole. After tiie formation of these four 

 meridional sections, by the two furrows, a third furrow passes 

 around the equator and separates the dark from the light hemis- 

 phere very sharply. The third segmentation furrow in Triton and 

 in Bombinator differs from Amblystoma in being not equatorial, 

 but nearer the upward pole. From this ])oint segmentation pro- 

 gresses quite rapidly and at different rates in the two color areas ; 

 it being much more rajiid in the lighter one. As the segments 

 begin to get quite small, more and more color makes its appear- 

 ance in the light area until as segmentation is about completed, 

 only a small light area is left at the lighter-colored or downward 

 pole. At the time when the first two furrows are complete there 

 may be seen on the different segments near the light pole, a few 

 small depressions in the substance of the yolk, the " trous vitellins " 

 of Dr. Van Bambeke.f They soon disappear however, being 

 visible for a few hours only. Upon examination, it is readily seen 

 that segmentation progresses much more rapidly in the light 

 hemisphere, and that it is carried on with very little regularity, 

 in either. When the egg has finished segmentation the entire sur- 

 face has become dark colored with the exception of a small irreg- 

 ular area surrounding the lighter |)ole and stretching away from it 

 in one direction. The cells or segmentation-masses immediately 



*Vide Der Unkc, p. 53. 

 f Bulletins de I'Academie royale de Belgique, 2'^ serie,Tom XXX, Nr. 7, 1870. 



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