No. 3.] - BASIS OF THE AMPHIBIAN EMBRYO. 473 
fold had formed, and the position of the exovate was found 
to be slightly at the right of the median line and in the 
posterior end of the embryo, as shown in Fig. 8o. 
At 3 p.m. April 4, an egg in which the blastopore had 
reached the crescentic form (Fig. 81) was punctured a short 
distance above the blastoporic opening. At g a.m. on the 
following morning the blastopore had narrowed to a small, 
circular opening, as shown in Fig. 82. At 6 P.M. the neural 
fold became visible, and the exovate was found to occupy a 
position considerably at the left of the median plane, and in the 
posterior end of the embryo (Fig. 83). 
At 3 p.M., April 4, an egg in the stage of crescentic blastopore 
was selected, in which a group of peculiar accidental markings 
were present near the blastopore, as shown in Fig. 84. At 9 P.M. 
the blastopore had changed to the form shown in Fig. 85. It 
will be observed that the mark above the blastopore has passed 
toward the blastoporic margin at about the same rate observed 
in the progress of the exovates in the three preceding experi- 
ments. At 6 a.m. on the following day the blastopore had 
almost reached the circular form, as shown in Fig. 86. The 
mark above the blastopore has passed entirely within, while 
those below are about to disappear. In following the successive 
steps represented by Figs. 84-86, it is plain that a change has 
occurred in the relative positions of these markings; this shift- 
ing has undoubtedly been brought about through lateral pressure, 
which is now revealed by the greatly elongated and narrowly 
compressed cells. 
At 3 p.m., April 4, an egg in the early blastopore stage was 
punctured at a point 20° to 25° below the centre of the 
crescentic line, as shown in Fig. 87. At 5 p.m. the blastopore 
had changed to the semicircular form indicated in Fig. 88. The 
exovate and dorsal lip of the blastopore are now appreciably 
nearer to each other. At 11 p.m. the blastopore had reached 
the stage shown in Fig. 89. The exovate, however, does not 
seem to have changed its relative position. At 6 a.m. on the 
following day the circular blastopore was completed (Fig. go), 
the distance between the exovate and the dorsal lip being now 
greatly diminished. At 11 a.m. the circular blastopore was 
