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will see that in ontogeny this backward shifting of the- 
blastopore, being the future neurenteric canal, is quite evident. 
We then have to assume that the stomodaeum has lost its 
original function and a new, secondary mouth had to be 
formed. This gives us at the same time the solution of 
the problem of “the old mouth and the new” (BEARD, 
1888, a), of the palaeostoma and the neostoma of KUPFFER - 
(1894) and shows us clearly, how the old mouth could 
have been lost and why a new one had to be formed in 
a way which reminds us of the Deuterostomia. This new 
mouth accordingly breaks through only very late in embryonic 
life, as DOHRN first emphasized (see quotation above). 
Moreover we will see in the second chapter that the- 
new mouth in Ascidians, Amphioxus and Craniates is formed 
in three different ways and, as a consequence, is not homo- 
logous in these three groups. This points equally to the- 
secondary nature of the Vertebrate mouth. 
Neuropore. — The primary mouth, being that of the Anne- 
lias, is represented by the neuropore of Amphioxus, and 
this itself again is phylogenetically secondary in respect 
to the „Urmund”, the mouth of the hydroid polyps, which 
in Annelids we find again in the cardiac pore, and in 
Chordates in the neurenteric canal, both representing the 
former blastopore. Thus in the ontogeny of Vertebrates-. 
we see the three successive mouths appear in the same 
Succession as they appeared in phylogeny : the blastopore 
(“Urmund”), the neuropore (the Annelidan mouth) and 
finally the definitive mouth. 
askell. — It truly seems a bold supposition that a part 
of the alimentary canal should have changed its function 
and have become the central nervous system. Yet, as we- 
will see especially in the last chapter, the facts of embryo- 
logy plead so strongly for it that KOWALEWSKY and the 
writer are not alone in their idea. A somewhat similar 
suggestion has been made by the physiologist GASKELL (1908) 
in his theory on the origin of Vertebrates. More than once, . 
in conversation and in correspondence, l have heard my theory 
compared with that of GASKELL, a comparison which |l must 
add at once did not exactly flatter me. 1 readily believe - 
that GASKELL was a good physiologist, but I cannot: 
admire his phylogenetic speculations, to which | think my 
theory bears only a superficial resemblance. GASKELL derives 
the Vertebrates from Arthropod-like ancestors by making 
