1212 
SCANDINAVIAN FISHES. 
brain. Here in Branchiostoma there is hardly any such 
swelling: — the spinal cord is a string of almost uni- 
form thickness, gradually tapering backwards, and only 
slightly dilated at its anterior end (fig. 366, a) so as 
Fig. 366. Anterior end of the spinal cord and the nerves thereof in 
Branchiostoma lanc-eolatum , seen from above and magnified. After 
Vogt and Yung. 
a. medullispinal swelling and its cavity; b, first, c, second pair of 
nerves; d, pigment Spot ( eye spot?); e, third and fourth pairs of 
upper (posterior, sensory) nerves; /, spinal cord. 
Fig. 367. Caudal end of Branchiostoma lanceolatum, seen from the 
left and magnified. After Vogt and Yung. 
a, spinal cord; b, notochord; c, upper ramifications of the sensory 
nerves; d, lower ramifications of the same; e , hindmost myocomma 
(boundary of the hindmost myomere). 
to form a kind of cerebral vesicle. And the notochord 
tapers to a pointed termination at each end of the body. 
A peculiarity never seen in any vertebrate higher than 
Branchiostoma, is that the notochord (fig. 365, Ch) 
projects forward beyond the anterior end of the spinal 
cord {My) and in front of the mouth aperture (/ and g). 
At the posterior end of the body the case is different. 
There (fig. 367) we find an upcurved dilatation of 
the medullispinal canal (a), reminding us of Myxinc 
(fig. 354). 
The mouth is of a curious structure for a verteb- 
rate. It is neither a prehensory nor a suctorial mouth; 
it is, so to say, merely a deglutitory mouth, edged 
with a ring of small cartilages (fig. 365, /), in texture 
resembling the notochord. Each one of these cartilages 
gives out a process (g) to form a support in one of 
the so-called cirri which surround the oral aperture 
Fig. 368. Posterior wall of the mouth cavity (postoral sphincter or 
velum ) with its twelve centripetally meeting cirri, which are furnished 
with the sensory bodies first described by Langerhans, bundles of 
sense-hairs on thickened parts of the epithelium. After Ray Lankester. 
outside, but are folded inwards when the mouth is 
closed. These cirri are almost exactly similar to the 
sense-filaments or tentacles possessed by many of the 
lower animals. At their base they are united to a 
membrane coursed by muscular fibres; and their sur- 
face is clothed with a cylindrical epithelium, among 
whose cells some are ciliated, others prolongated out- 
wards into stiff setae, which are collected in verruciform 
bundles, and connected inwards with nerve fibrillae, 
whence they have been interpreted as organs of taste. 
Within the mouth is a buccal (pharyngeal) cavity, 
the inner surface of which displays active ciliary mo- 
tion, especially along the margins of a number of 
