111 
head-fold, opposite the place where the blastopore closes. 
The results described above point to the general pre- 
valence of a relation between the animal pole of the egg 
and the anterior border of the cerebral plate, as might be 
expected from my theory. For the sake of completeness Î 
must mention here that HELEN DEAN KING (1902) in Bufo 
and EYCLESHYMER (1902) in Necturus concluded from 
Similar pricking experiments that in these forms the 
animal pole is found some distance in front of the 
transverse brain-fold and that the latter lies even halfway 
between the animal pole and the equator. However, 
it seems to me that the evidence yielded by these expe- 
riments is not so conclusive as to preclude the possibility 
that on re-examination these forms also might turn out 
to conform with the rule found to be valid for such closely 
allied species. 
Acrania and Craniata,— In the foregoing chapter we 
have pointed already to the fact that the relation of the 
animal pole to the cerebral plate in Amphioxus is a different 
one from that in Craniata. In Amphioxus, as shown by 
CERFONTAINE's (1906) figures, the place of the animal 
pole is often indicated until the gastrula-stage by the second 
polar body which remains fixed to the egg. Here also the 
closure of the blastopore occurs nearly opposite the animal 
pole, but a comparison of a gastrula where the polar body 
is still present, as represented in fig. 12, with a somewhat 
older stage, with a neuropore but where the polar body 
has been lost (fig. 5), renders it quite evident that, if in the 
latter the polar body were still present, it would be found 
at a considerable distance in front of the neuropore. In 
both Acrania and Craniata the animal pole lies at the 
anterior end of the embryonic rudiment, in corresponding 
places with regard to the main axis of the embryo and to 
the place where the blastopore closes (with regard to the 
latter circumstance exception must be made for very yolk- 
laden eggs). The neuropore in Craniata however lies ter- 
minally and close to the animal pole while in Acrania it 
IS situated dorsally, a good distance away from the animal 
pole. This is one of the circumstances which, in the fore- 
going chapter, has induced me to conclude that the prae- 
chordal part of the brain of Craniates is not yet present 
In Acranía, In reality, however, | first made this conclusion 
from other reflections (1913) and only afterwards, by the 
