AMPHIOXUS 461 
behind the mouth to the atriopore, and into which the gill- 
slits of the pharynx open in the adult. 
Skin.—The epidermis consists of a single layer of cylin- 
drical cells. Some of them project slightly from the surface, 
Ph. 
alr, 
Fic. 249.—Transverse section through pharyngeal region of 
Amphroxus.—Alter Ray Lankester. 
sf.c., Spinal cord; c/., notochord, beneath which lie the two dorsal 
aorte; mz., myotome; a.c.f, atrio-ccelomic funnel, opening 
into sub-chordal coelom; C., cecum; G., a genital sac with 
ova; 7zp., metapleural fold; @/~., atrial cavity; P%., pharynx, 
with dorsal and ventral grooves, and bars between gill-stits, 
Note in the primary bars and in the ventral groove the small 
cozlomic spaces. The ectoderm ‘is dark throughout. 
and are connected at the base with nerve-fibres. These are 
sensory cells, and may be compared to the cells of the 
lateral line in fishes and tadpoles. Here, however, they 
are scattered over the surface of the body, though especially 
