134 
the shape of a crescent and the border of which (fig. 35%), 
as further development shows, indicates the limit of the 
head as far as the gill-slits. On this plate two suckers, 
the mouth and the two olfactory grooves are afterwards 
found. Further experiments have shown me, that the mark 
c is generally found a little distance further behind the 
fold which represents the border of the sense-plate than 
indicated in fig. 2 of my publication of 1916 and that as 
a consequence we probably can not think of a closer 
relation between the so-called sense-plate and the apical 
plate of a trochophore as alluded to at that time (p. 9). 
The mark d also does not alter its position in a marked 
way. It is found again in the region where afterwards the 
gill-slits will break through. 
he above results were published by me in 1916. Since 
then l have repeated and completed these experiments and, 
by using specially sharpened hedgehog quills, have now 
succeeded in making marks not only at the animal but 
also at the vegetative pole, i. e. at the opposite point of 
intersection of the first two cleavage-furrows, where the 
yolk accumulated here renders marking more difficult since 
a little lesion causes the yolk to protrude in great quantity. 
During further development, during cleavage and gastru- 
lation, the mark at the vegetative pole did not change In 
the least its position with regard to the one at the animal 
pole. After the blastopore border had appeared it was 
found just in front of the ventral lip within the white area 
and finally it was lying at the place where the blastopore 
closes to a short slit, still right opposite the mark at the 
animal pole. This shows that the white endodermic area 
does not change its position at all while the blastopore 
border is overgrowing it and while at its periphery the 
smaller endoderm cells are proliferating and by sinking In 
and splitting are forming the archenteric cavit 
he results obtained with Rana esculenta and Ambly-_ 
stoma tigrinum agree on the whole with those on Rana fusca. 
The closure of the blastopore, however, does not occur 
exactly opposite the animal pole as in the latter form. In 
less than 180° of the circumference of the egg, whereas in 
Amblystoma it is situated somewhat more to the ventral 
side, the base of the embryo extending here dorsally over 
