310 CHORDATA. 
which is the mouth, surrounded by four pairs of small buccal 
cirri. Above the mouth is a small median aperture usually 
termed the xasal opening. It leads into a tube, the 
pituitary sac, which also has an internal opening into the 
pharynx. 
The single olfactory sac opens into the pituitary sac near 
its external aperture. The mouth is situated at the base of 
a suctorial buccal funnel, on the dorsal wall of 
which is a large median horny tooth. Other 
horny teeth are attached to a large tongue which is moved 
by enormous muscles. 
Myxtne is an active carnivorous animal and often devours 
fish caught on the lines. It is indeed frequently so caught 
itself. ‘Ihe edges of the buccal funnel are said to form a 
sucker, and the movements of the tongue serve to rasp the 
flesh of its victim. The mouth passes into a pharynx 
continued backwards into:a wsophagus. The pharynx 
has six pairs of lateral openings which pass outwards 
into large branchial sacs (or gill-pouches) containing the 
gills. From each of these a canal leads back- 
wards. Those of each side unite to open by a 
single branchial aperture situated ventro-laterally. Behind 
the last branchial sac the cesophagus has a duct on the left 
side (the wsophageo-cutaneous duct) leading directly to the left 
branchial aperture. When the mouth is being employed 
the respiratory current passes through the pituitary sac to 
the gills. The cesophagus expands into an intestine which 
receives a dile-duct from a simple dilobed liver. ‘There is a 
small gall-bladder. The intestine terminates ventrally in an 
anus, 
The xotochord consists of a skeletal chordoid rod running 
from below the mid-brain to the tip of the tail. It is sur- 
Skeletay, YOUnded by a thick sheath. A membranous 
* sheath also surrounds the nerve-cord. There 
is no trace of a vertebral column. Cartilage is found in 
rings supporting the ‘‘nasal passage,” and the buccal cirri 
are supported by cartilages. Under the brain there lies a 
ventral cartilaginous portion of a cranium, completed dor- 
sally by membrane. A trace of visceral arches may be 
represented by a sudocular bar and other cartilaginous 
structures connected with it, united with the cranium. 
Alimentary. 
Respiratory. 
