348 



lines in Fig. 2. Seven of these eggs developed and in these the ex- 

 ovates occupied the following positions: 



In one egg (Fig. 8) the exovate lies a the right of the median 

 plane and far within the transverse portion of the neural fold. 



In a second egg (Fig. 9) the position of the exovate is exactly in 

 the median line and in the anterior end of the neural groove. 



In a third egg (Fig. 10) the exovate lies in the transverse portion 

 of the neural fold and at the left of the median line. 



In the fourth and fifth eggs (Figs. 11, 12) the exovates lie in, or 

 near, the transverse portion of the neural fold and again at the right 

 of the median plane. 



In the sixth and seventh eggs (Figs. 13, 14) the exovates lie, as 

 in the third egg, on the left of the median plane and within the 

 neural fold. 



The results of this series of experiments indicate that the trans- 

 verse portion of the neural fold differentiates in an area lying midway 

 between the upper pole of the egg and the dorsal lip of the blastopore. 



Series III. Twenty eggs in the same stages as those in series II 

 were punctured at the upper pole of the egg, as indicated by the 

 cross-lines in Fig. 3. Six of these eggs developed. 



In one egg (Fig. 15) the exovate lies just without and to the 

 left of the anterior end of the embryo. 



In two eggs (Figs. 16, 19) they lie to the left, at the level of the 

 anterior end of the embryo but far removed from the median plane. 



In three eggs (Figs. 17, 18, 20) the exovates lie close to the 

 median line but far in front of the anterior end of the embryo. 



The experiments indicate that the area in which the punctures 

 were made later occupies a position in front of the embryo, in other 

 words the head of the embryo forms on the blastoporic side of these 

 punctures. 



In Figs. 21, 22, 23, I have represented the successive stages which 

 an accidental mark occupied during the formation of the blastopore. 

 Its sucessive positions leave no doubt but what a process of infolding 

 is going on at the dorsal lip of the blastopore, precisely as I, among 

 others, have witnessed during the gastrulation of other Amphibia. 



I have represented in Figs. 24, 25 two positions occupied by a 

 slight artificial abrasion. While this is the only observation on this 

 point and should not therefore be given too much weight, it points 

 toward a like process going on at the ventral lip of the blastopore. 



In one egg (Figs. 26, 27) an artificial mark was observed at the 

 position indicated in Fig. 26, after the embryo had become visible 



