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4. The displacement of the endodermic area from opposite 
the animal pole to the future dorsal side in the eggs 
of lower Vertebrates is to be explained by a similar 
displacement to the ventral side during the early 
development of Annelids. 
5. The caudad-eccentric closure of the blastopore, typical 
for Chordates, is a result of the interference of th2 
contraction of the blastopore border with the backward 
shifting of the blastopore as a result of the elongation 
of the medullary tube — former stomodaeum — which 
in ontogeny occurs before this tube has been formed. 
Relation of anus and blastopore. — We shall pass now to 
the question of the relation of the anus to the blastopore, 
yet another question of Vertebrate embryology on which the 
greatest uncertainty and confusion reign and which indeed, 
as l hope to show, could hardly have been solved without 
the aid of my theory. 
The statements made by the numerous investigators on 
this subject are so divergent that it must be very difficult 
for any one who can not judge from personal experience 
to form a sound opinion. I shall try to show that the 
application of the principles of my theory on the origin of 
Vertebrates will once more serve to furnish us with the 
solution of an old problem which has been resuscitated, 
especially, by GROBBEN's (1900) classification of the animal 
kingdom. In the first place the different views and results 
of former investigators may be briefly reviewed. We shall 
confine ourselves mainly to the Amphibian egg, in which 
a relation between anus and blastopore was noticed for 
the first time. Anurans and Urodelans will be treated 
separately because, as [ can confirm from my own invest- 
igations on Rana esculenta and Amblystorna tigrinum, these 
two groups exhibit a notable difference in the relation of 
the anus to the blastopore. We shall begin with that group 
on which the first observations were made, the Anurans. 
Different views on Anurans. — BALFOUR (1881), in his 
Text-book, gives a description of the origin of the anus, 
based mainly on the figures of GOETTE (1875) for Bom- 
binator igneus and his own investigations «on Rana 
temporaria where the anus breaks through somewhat earlier 
than appears to be the case in toads generally. The blas- 
topore passes into the neurenteric canal and the anus 
eventually arises at the bottom of a diverticulum of the 
