SKIN. 



413 



lateral line in fishes and tadpoles. Here, however, they 

 are scattered over the surface of the body, though especially 

 abundant on the buccal cirri. The epidermis lies upon a 

 thin layer of clear cutis. 



PL- 



ax.]. 



Fig. 178. — Transverse section through pharyngeal region of 

 Amphioxus. — After Ray Lankester. 



sp.c, Spinal cord ; nek., notochord, beneath which lie the two dorsal 

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

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

 ova ; 7«A, 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. 



Beneath this there is a layer of fine tubes, which unite in a longitudinal 

 canal running along each metapleural fold. These metapleural canals 

 are said by some to arise in development by a splitting of an originally 

 solid mass (schizoccelic) ; but it seems more probable that they aie 

 morphologically portions of the true ccelom — ventrolateral extensions 

 of the " collar-ccelom " (enteroccelic). 



