207 
and the soft palate, and are innervated by the gustatoyr 
branches of the N. trigeminus, facialis and glossopharyngeus. 
rotostomia, Deuterostomia, Tritostomnia,. — We have come 
to the conclusion that the old distinction by HATSCHEK of 
the three groups Zygoneura, Ambulacralia and Chordonia 
is to be piefered to GROBBEN’s division into Proto- and 
Deuterostomia, since the latter group does not constitute a 
natural unit. HATSCHEK and his assistant SCHNEIDER have 
also been inclined to unite their Ambulacralia and Chor- 
donia into one group, the Enterocoela, in which the 
coelomic mesoderm is of entodermal origin, whereas ín the 
Zygoneura or Ecterocoela it would be of ectodermal origin 
(cf. HATSCHEK, 1611, p. 18). That this last opinion is erro- 
neous has been conclusively demonstrated by the cell-lineage 
investigations. 
My theory, on the contrary, would rather point into the 
direction of a union of the Chordonia with the Zygoneura, 
from which they are to be derived. Yet a subdíivision of 
the “Coelomata”, the three-layered Metazoa, into three groups 
is no doubt the more preferable method. In GROBBEN's 
nomenclature we could designate these three groups as 
Protostomia, Deuterostomia and Tritostomia. 
In the first group the primordial opening of the gut to the 
exterior, the blastopore, becomes the ingestion-opening. In 
the second group it passes into the anus and a second 
opening becomes the mouth. In the Tritostomia the first 
and the second opening pass into the canalis neurentericus 
(former ingestion-opening) and the anus, while the mouth 
breaks through only late in embryonic life as a third opening. 
To the question if there is any relation of the anus to the 
blastopore we will revert in the last chapter. There l hope 
to show that not only the application of the principles of 
my theory will bring us the solution of the old problem of 
the relation between anus and blastopore, which will prove 
to be a secondary one, but also that, considered in the light 
of this solution, the facts to be observed yield one of the 
strongest supports in favour of the view that the neural 
tube indeed represents nothing but the former stomodaeum 
that has grown out in caudal direction as far as the pos- 
terior end of the body and even further still (formation of 
the tail). 
