TO THE EMBRYOLOGY OF AMPHIBIA. 21 



At 10:30 a.m., next morning (April 30th., the fourth day 

 after deposition), the blastopore was nearly closed, leaving only 

 a small yolk-plug, and the general outline of the neural plate 

 could be well recognized. Fig. 36 gives the left side view, and 

 Fig. 37 the posterior view of the egg at this stage, sketched 

 respectively at 10:37 and 10:50 a.m. These figures show that 

 the dorsal lip of the blastopore has again grown a little down- 

 ward while the position of the blastopore remains nearly unaltered. 

 This is probably due to the fact that the rotation of the egg 

 had ceased before the closure of the blastopore was finished, and 

 thus bereft of the counterbalancing movement the downward 

 growth of the dorsal lip toward the center of the blastopore is 

 able once more to make itself felt. It seems to me that this is 

 a strong argument in favour of the view that the blastopore is closed 

 by the overgrowth of its lip all around its circumference. 



Fig. 38 shows the left, side view of the egg on the morning 

 of May 1st., (the fifth day). The neural groove is already closed, 

 and the first traces of the mandibular arches, the optic vesicles 

 etc. are visible. 



The facts brought out by the study of this egg (Egg C) 

 are as follows : — 



1). The entire lip of the blastopore, the dorsal, ventral and 

 lateral parts, grow equally from all around toward the center of 

 the blastoporic area, from the first until the blastopore is com- 

 pletely closed, although at certain late stages, this is obscured by 

 the rotation of the egg. 



2). The rotation of the egg as a whole by which the dorsal 

 blastoporic lip is again brought back to its first starting point begins 

 when the dorsal lip has grown downwards over the yolk mass about 

 70°, proving that the dorsal lip never travels beyond the yolk-pole, 



