206 
HEYMANS and VAN DER STRICHT (1898) in studying the 
ontogeny of the spinal nerves could not detect spinal ganglia. 
This is indeed a difficulty from the point of view of my theory 
which Il will not try at all to diminish by any far-fetched 
hypothesis. The only thing we can do is to assume that 
the spinal ganglia have fused with the medullary tube or 
have disappeared in the same way as all the sense-organs 
and the cerebral ganglia have been lost by Amphicxus 
which, as we will see, exhibits, in addition to its primitive 
features, many peculiarities which point to degeneration. 
No stomodaeum in Chordates. — lt is in accordance with 
my theory that in lower Vertebrates, in Amphioxus, Asci- 
dian larvae and Appendicularia nothing like the ectodermal 
stomodaeum of the Zygoneura or Protostomia is tound. 
The whole oesophagus is entodermal and the cardía is some- 
thing quite different from the cardiac pore of Annelids. The 
mouth, breaking through only very late in embryonic develop- 
ment, leads directly into the entodermal branchial basket. 
Taste in Chordates. — Now if our supposition is right that 
the stomodaeum was one of the first sense-organs, that of 
the taste, we must conclude that the Chordates would have 
lost this important sense, if they have not acquired a sub- 
stitute. Probably the neural gland of Tunicates may be 
explained in this way. This peculiar organ, opening by the 
ciliated funnel in the roof of the anterior part of the bran- 
chial basket, originates from the central nervous system, as 
was pointed out by KOWALEWSKY (1866) for the Ascidians 
and by myself for the Appendicularia (1912). Evidently a 
new communication between the former stomodaeum and 
the gut was established after the old one had atrophied, 
originating as a diverticulum from the so-called brain-vesicle, 
afterwards separating from it and thus giving rise to a litile 
ciliated funnel-shaped sense-organ of ectodermal origin in the 
entodermal gut-wall. It remains in close connection with 
the cerebral vesicle, the swollen anterior end of the medullary 
tube, the former stomodaeum. 
In Amphioxus and the Craniata we see arise an ectodermal 
involution, the oral cavity, into which in Craniata the end- 
buds — in fishes still widely distributed in the mouth, the 
branchial cavities and the outer surface of the head, in 
some even over almost the whole surface of the body— 
gradually concentrate to form the taste-buds which in higher 
Craniates are chiefly confined to the epithelium of the tongue 
