412 



CEPHALOCHORDA, AMPHIOXUS. 



Skin. 



The epidermis is a single layer of columnar cells. Some 

 of them project slightly from the surface, and are connected 

 at the base with nerve fibres. These are sensory cells, and 

 may be analogous with the cells of the lateral line in fishes 

 and tadpoles. The epidermis lies upon a thin layer of clear 



a.c.f. 



atr. 



Fig. 133. — Transverse section through pharyngeal region of 

 Amphioxus. (After Ray Lankester.) 



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

 aortse ; ?;;., myotome; a.c./., atrio-coalomic funnel; C, csecum ; 

 G.^ a genital sac with ova ; mp., metapleural fold ; atr. 'iatrial 

 cavity; /'/z., pharynx, with dorsal and ventral grooves, and bars 

 between gill slits. 



cutis. Beneath this there is a layer of fine tubes, which 

 unite in a longitudinal canal running along each metapleural 

 fold. These metapleural canals may be derived from the 



