226 Boyal Sociefi/ : — 



For its recei)tion; while Seinptn'*, in a latt-ly published paper, sepa- 

 rates it i'rom the Vertebrata altogether. 



In a recent eonununication to the Linnean Society, I have de- 

 scribed w hat I believe to be the representative of the duet^ of the 

 WollHan bodies, or "primordial kidneys" of the higher Vertebrata, 

 in Amphio.viis ; and 1 ])ropose, in this preliiniiiarv Tiotice, to point 

 out that although Amphioxus has no completely diifereutiated 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 a])erture of Amphioxnis 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 vdum 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 of¥ 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 (//,/, t% f?, c) 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 

 (b and a) pass in front of the first myotome; and the nerve a 

 runs parallel wath 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. 



In the Marsipobranch fishes My.vine and Ammocoetes (now knowii 

 to be a young condition of Petromyzon) a velum also separates the 

 buccal from the branchial cavity (figs, B, C, D). But this velum 

 is in connexion with the hyoidean arch. The resemblance of the 

 buccal cavity, with its tentacles, in Ammocoetes to the corresponding 

 cavity in Amphiomis is so close, that there can be no doubt that 

 the two are homologous. In the Ammocoetes there is a hyoidean 

 cleft which has hitherto been overlooked. The auditory sac lies 

 at the dorsal end of the arch and above the dorsal attachment of 

 the velum. The latter, therefore, corresponds ^\ith the auditory 

 region of the skull ; and the nerve h should answer to the last of the 

 pneauditory cranial nerves, Mhich 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 Ampldoxus 



* "Die Stammverwandtschaft cler Wirboltliiere und Wirbellosen," Arbeiten 

 aus dein zool.-zootoni. Institut in Wiirzburg. Bd. ii. 1874, p. 42. 



