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, 



a.c.f. 



mp* 



>atr. 



FlG. 249. Transverse section through pharyngeal region of 

 Amphzoxus. After Ray Lankester. 



s^.c., Spinal cord ; nc/i., notochord, beneath which lie the two dorsal 

 aortae; /., myotome ; a.c.f., atrio-coelomic funnel, opening 

 into sub-chordal coelom ; C., caecum ; ., a genital sac with 

 ova; ;;/^., metapleural fold ; atr., atrial'cavity ; Ph., pharynx, 

 with dorsal and ventral grooves, and bars between gill-slits. 

 Note in the primary bars and in the ventral groove the small 

 ccelomic 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 



