226 Royal Society :— 
for its reception; while Semper*, in a lately published paper, sepa- 
rates it from the Vertebrata altogether. 
In a recent communication to the Linnean Society, I have de- 
scribed what I believe to be the representative of the ducts of the 
Wolffian bodies, or “ primordial kidneys” of the higher Vertebrata, 
in Amphiowus ; and I propose, in this preliminary notice, to point 
out that although Amphiowus has no completely differentiated brain 
or skull, yet it possesses very well-marked and relatively large 
divisions of the cerebro-spinal nervous axis and of the spinal 
column, which answer to the encephalon and the cranium of the 
higher Vertebrata. 
The oral aperture of Amphiowus is large, of a long oval shape, 
and fringed by tentacles, external to which lies a lip, which is 
continuous behind with the ventro-lateral ridge of the body. The 
oral chamber is spacious, and extends back to the level of the 
junction between the sixth and seventh myotomes (fig. A). Here 
it is divided from the branchial cavity by a peculiarly constructed, 
muscular velum palati, the upper attachment of which to the 
ventral aspect of the sheath of the notochord lies vertically below 
the anterior angle of the seventh myotome. 
Eight pairs of nerves are given off from the cerebro-spinal 
axis as far as this point. The eighth, or most posterior, of 
these, which, for convenience, may be called h, passes out between 
the sixth and seventh myotomes, and runs down parallel with the 
lateral attachment of the velum. The next five (g, f, e, d, ¢) pass 
out between the first six myotomes, and are distributed by their 
dorsal and ventral branches to those myotomes, to the integument, 
and to the walls of the buccal cavity. The foremost two nerves 
(6 and a) pass in front of the first myotome; and the nerve a 
runs parallel with the upperside of the notochord to the end 
of the snout, giving off branches to that region of the body 
which lies in front of the mouth. This nerve lies above the eye- 
spot. 
i: In the Marsipobranch fishes Myaine and Ammoceetes (now known 
to be a young condition of Petromyzon) a velum also separates the 
bueeal from the branchial cavity (figs. B,C, D). But this velum 
is in connexion with the hyoidean arch. The resemblance of the 
buceal cavity, with its tentacles, in Ammocetes to the corresponding 
cavity in Amphioaus is so close, that there can be no doubt that 
the two are homologous. In the Ammocetes there is a hyoidean 
cleft which has hitherto been overlooked. The auditory sac les 
at the dorsal end of the arch and above the dorsal attachment of 
the velum. The latter, therefore, corresponds with the auditory 
region of the skull ; and the nerve / should answer to the last of the 
preauditory cranial nerves, which is the portio dura, Assuming 
this to be the case, though the detailed homologies of the cranial 
nerves of the higher Vertebrata are yet to be worked out, it follows 
that the segment of the cerebro-spinal axis which in Amphiowus 
* “Die Stammverwandtschaft der Wirbelthiere und Wirbellosen,” Arbeiten 
aus dem zool.-zootom. Institut in Wiirzburg, Bd. ii. 1874, p. 42. 
