164 



INTERNAL FACTORS 



IV. i 



it is stated that the egg-axis becomes inclined to the vertical. 

 This would seem to be an error, due to a confusion between the 

 original white area and the white area enlarged by the addition 



FIG. 79. Diagrams of the closure of the blastopore in the egg of the 

 common Frog (R. tempomria). In A-D the egg is viewed from the vegeta- 

 tive pole, in E, F from below. The dorsal lip is at the top of the figures. 

 In D the ventral lip has just been formed and the blastopore is circular. 

 In E the rotation of the whole egg has begun, and in F is complete. 

 * 



of the grey crescent (compare Fig. 44 with Fig. 78). The 

 egg is now bilaterally symmetrical about the plane which 

 includes the egg-axis and the middle point of the crescent. 



