222 



lips (tne depression is shown at x in Fig, 13 a, b, c), indicating that 

 the two lips overgrew the yolk at about equal rates. Summary of 

 experiment : individual yolk cells were seen to be covered up by the 

 ventral lip; a natural mark near the centre of the blastopore area 

 was equally approached by the dorsal and ventral lips. 



Still another similar experiment may be selected for description. 

 An egg, in which the dorsal lip had just made its appearance, was 

 compressed and inverted at 10,45 A.M. The entire blastopore lip 

 was not outlined as an edge until 12,45 P.M. At 1 P.M. the dia- 

 meter of the compressed egg being 1,7 mm, the diameter of the 

 blastopore was 1,152 mm. A 3 P.M. (Fig. 14 a) the blastopore 

 measures 1 mm in the dorso-ventral diameter. The reference line 

 1 points to the apex of a cell 48 (.i from the ventral part of the 

 lip; the lip reaches the cell apex at 3,40 P.M. (the light was such 

 that, as indicated in the figure, a whole row of yolk cells could 

 plainly be seen; and the steady approach of the lip to the serrated 

 line, formed by their ends, made a very satisfactory observation). 

 — The condition of the blastopore at 3,45 P.M. in this egg, is 

 shown in Fig. 14 6. Reference line 2 points to the apex of a yolk 



Fig. 14. Successive views (a, b, c) of the blastopore of a compressed egg. d, I. 

 dorsal lip. v. I. ventral lip. 



cell 84 (.1 from the dorsal part of the blastopore lip ; at 4,20 P.M., 

 the dorsal lip is only 48 (.i from this cell apex. Reference line 

 1 points to the apex of a yolk cell (others indicated on each side). 

 This apex is at 4 P.M., GO (.i from the ventral part of the lip; at 

 4,30 P. M., the lip reaches the apex. — The blastopore at 4,30 P.M. 

 (dorso-ventral diameter of blastopore is now 0,768 mm) is shown in 

 Fig. 14 c. The reference line 1 points to the apex of a cell, which 

 at 4,45 P.M. is 72 /< from the ventral part of the lip ; at 5,40 P.M. 

 it is barely 24,« from this lip. Summary of experiment: Yolk cells 

 were seen to be covered up both by ventral, and by dorsal lips. 



