114 INTRODUCTION TO CLASSIFICATION. 



There is a cartilaginous skull, devoid of cranial bones ; but no 

 mandible, nor any traces of limbs. The notochord is persistent 

 and no centra of vertebrae are developed. 



The heart presents an auricle and a ventricle. The gills are 

 sac-like, and not ciliated. 



These fishes have a distinct brain and auditory organs ; and 

 the liver and kidneys are constructed upon the ordinary verte- 

 brate plan. 



6. The PHARYNGOBRANCHII. Neither cartilaginous nor 

 osseous skull, nor mandible, nor any limbs, are developed, The 

 persistent notochord extends beyond the cerebro-spinal axis to 

 the anterior end of the body, whereas in all other Vertebrata 

 it stops behind the pituitary gland. 



There are no vertebral centra or arches. No distinct brain 

 exists, nor any auditory organs. 



There is no heart, but several of the great vessels are rhyth- 

 mically contractile. The walls of the pharynx are perforated 

 by many slits, and ciliated. The liver is sac-like, and no kidneys 

 have been discovered. 



This order is represented by the single species Anyphioxus 

 lanceolatus. 



