CHORDATA. 143 



Subphylum C. Cephalochprda (Pharyngobranchii, 



Acrania). 



Marine Chordata with a continuous median fin but no paired fins. 

 Axial skeleton represented by the notochord which extends from one 

 end of the body to the other. No skull, jaws, true brain, sympathetic 

 system, auditory organ, heart or spleen. An unpaired eye as a pigment- 

 spot in the brain substance, and an unpaired olfactory pit. Blood 

 colourless. Body-cavity an enteroccele. Excretory organs as a pair of 

 short tubes opening into the atrial cavity surrounding the pharynx, this 

 cavity opens to the exterior by an atriopore. Gonads arranged rneta- 

 inerically ; no gonaducts. Only one known genus. Amphioxus lanceo- 

 latus, lancelet. 



