NO. 584] B1LA TERALITY IN VERTEBRATES 513 



Experiments 



On June 5. 1S<)4, sixteen eggs in the thirty-two eell stage were punc- 

 tured at the equator, in the middle of the white cells, as shown in Fig. 



in the accompanying cut. The extraovates were found in the positions 



positions are doubtless due to my punctures falling at different points, 

 sometimes hitting as in Fig. 12. at other times in the very edge of the 



two showed no blastopore. 



On June 4, 1S94, pricked egg B at middle of lower pole, soon after 



trally this outline was not clearly marked. At 4:30 this blastopore was 

 outlined all around and nearly circular or about % diameter observed 

 at 3 :00. At 6 :30 the blastopore was far advanced and nearly circular. 

 At 8 :30 it was nearly closed. It will be noted that the extraovate re- 

 mained central throughout. 



Another egg C was punctured in the ventral edge of the blastopore 

 rim, and the extraovate was carried along by the closing blastopore. 

 I ought to have made two punctures, one in the middle as well so that 



along by this overgrowth, and one might imagine this puncture a fixed 

 point, approached by the blastopore from the opposite side. 



June 5. I pricked a number of eggs in the early cleavage stages 

 (8-64 cells) at lower pole. In most of these eggs the extraovates were 

 found after two to three hours to lie at or near the equator of the egg. 

 This was long before the appearance of the blastopore. The extra- 

 ovate has evidently moved and if one should leave the egg until the 

 blastopore appeared and then look at it, it might be found at the middle 

 of the body; and thus it might appear as if the embryo had lengthened 

 across the lower pole (Roux). Sometimes extraovates have moved and 



