236 



the glass. Once the ovate gets into this position, while the further 

 growth of the ventral lip across the yolk would of course go on, its 

 progress across the mirror would be interfered with by the ovate. 

 In this situation the continued growth of the ventral lip across the 

 yolk would produce a gradual total revolution of the egg, 

 in a direction opposite to that indicated by the arrow 

 in Fig. 16 ^^ And thus the dorsal lip would execute a movement 

 across the field, which would be in large pai't merely an apparent 

 movement across the yolk. It is, I believe, to this revolution of the 

 egg as a whole, caused by the ovate becoming pressed against the 

 glass, that the very excentric position of the blastopore (Fig. IG ^ '') 

 is due. — The other two eggs of this batch behaved in a different 

 way from the rest. In one egg, in which the ovate was very small, 

 the blastopore occupied a central position in the mirror picture at 

 1 A.M. Mar. 11 (Fig. 10^^), the ovate lying at the ventral lip. In 

 the other egg, the ovate, instead of becoming greatly flattened, be- 

 came rounded off and only slightly flattened; and in this egg, the 

 blastopore at 1 A.M. occupied a position not far from central, as is 

 shown in Fig. 16^^, with the ovate at tlie ventral lip. In these two 

 eggs, the ovate evidently did not affect, or did not materially affect, 

 the position of the egg as a whole. — Results such as those de- 

 scribed in the case of this experiment were obtained in the case of 

 other similar experiments. 



The results of the great majority of my experiments, in which 

 the ovate was produced opposite the dorsal lip (120 — 150*^ distant), 

 are substantially the same as those reached by Morgan ('93), in that 

 the ovate continues to remain at the ventral lip, during the gradual 

 approximation of the dorsal and ventral lips. Morgan's conclusion 

 rests however on the assumption that the ovate is a fixed point, and 

 therefore that the ventral lip is stationary, while the dorsal lip travels 

 120" across the yolk. Morgan however overlooks the not infrequent 

 indication that the ovate is shifted in the direction of the ventral lip 

 (Exp. 8 — from a position at an appreciable distance from the lip, 

 to it). Morgan also in interpreting his results, makes no use of 

 the evidence to be drawn from those experiments, in which the ovate 

 is produced in the centre of the black hemisphere, and at or just 

 al)ove the dorsal lip. The evidence from the latter kind of experiment 

 is that the ovate moves with the dorsal lip (Exp. 4, 5) — hence it is 

 a priori possible that the ovate at or near the ventral lip, moves 

 with that lip. The former kind of experiment Morgan says is un- 

 satisfactory (why?), but my results were very uniform, as where those 



