THE ORIENTATION OF THE FROG's EGG. 389 



line of separation of the black and white, and also indicates 

 the subsequent line of invagination of the remainder of the 

 blastopore. It will now be seen (fig. 11) that the point of in- 

 jury lies just outside of the pignaented line. At 12 midnight 

 the blastopore had grown much smaller (fig. 13), and the point 

 of injury was outside of the blastoporic rim. The point of in- 

 jury is now at less than half its former distance from the 

 dorsal lip of the blastopore. 



Experiment II (figs. 13, 14). — Egg at blastula stage, had 

 been kept overnight on ice to retard rate of development. At 

 9 a.m. the blastopore had appeared. Egg stuck in white at 

 a point not quite so far from the blastopore as in the last case. 

 At 4.30 p.m. the outlines of the whole blastopore to be seen, 

 but the point of injury, as before, is still outside of the blasto- 

 poric rim, and is nearer to the dorsal lip of the blastopore than 

 at first. 



Experiment III (figs. 15, 16). — In this egg the blasto- 

 pore appeared at first as a vertical pigmented line (fig. 15), 

 which soon extended laterally into the usual crescent. The 

 point of injury was nearly the diameter of the egg from the 

 blastopore. At 4.30 p.m. (fig. 16) the crescentic blastopore 

 was much nearer to the point of injury. Later stages not 

 followed. 



Experiment IV (figs. 17 — 19). — Stuck at 8 a.m. at 

 far edge of white, fig. 17. Blastoporic crescent already 

 formed. At 4.30 p.m., fig. 18, dorsal lip of blastopore 

 much nearer to defect. At 8 p.m. circular outline of blasto- 

 pore present, and defect lies just within the edge of the 

 blastopore. 



Experiment V (figs. 20, 21). — Stuck at 4 p.m. quite near 

 to the blastopore. Blastopore had already formed a crescent. 

 At 8 p.m. the dorsal lip of blastopore had nearly reached the 

 defect. 



Experiment VI (figs. 22, 23). — In this experiment the 

 lower pole was not stuck until the circular outline of the blas- 

 topore was formed (fig. 22). The dark line of the crescent 

 marks the dorsal lip of blastopore. The dotted line marks 



