THE l- l »// 7,7/) 141 



Class III. — M lrsipobb ln< mi t Lampreys, o ■ I 



General Characters of the CyclostomatMis Vertebrates. — 

 In the hag fish and lamprey, representatives of the jawli 

 Vertebrates, the body is long and slender, cylindrical, the 

 skinsmooth, scaleless, with only a median dorsal and Neu- 

 tral tin (or in Myxine only a small lower median fin); the 

 mouth is circular, and in the lampreys armed with numer- 

 ous conical teeth. There is no bony skeleton ; the spit 

 column is represented simply by a thick rod (dorsal cord, 

 uotocord) surrounded by a sheath. The skull is cartiL 

 inous, not movable on the vertebral column; is very impi - 

 fectly developed, having no jaws, the hyo-mandibular boi 

 and the hyoid arch existing in a very rudimentary 

 The few teeth present in the hag fish are confined to the 

 palate and tongue; those of the lamprey are numero 

 conical, and developed on the cartilages supporting the li 



The nervous system is much as in the fishes, the brain 



th its olfactory, cerebral lobes, thalami, opl . ml 



medulla being developed, the cerebellum in Myxine blend- tl 

 with, in the lamprey free from the medulla. The dig* 

 canal is straight, with no genuine stomach, but the liver - 

 much as in higher Verti • The respiratory 



are very peculiar, being purse-like cavities (whence the 

 name Marsipobranchii), in the lampn en in num- 



ber on each side of the pharynx, opening rnally by 



small apertures; internally they connect with a long cav- 

 ity lying under the oesophagus, and opening autcrioi 

 into the month. The heart is like that of fislx -. - 

 the kidneys. The eyes are minute, sunken in the head and 

 under the skin in the hag (M . but larger in the 



lamprey. 



Another extraordinary feature in tl 

 nasal aperture, as opposed to the \ n all h 



Vertebrates. The aperture leads to a sac, which in ti. 

 Myxi 9 communicates with the mouth (phari u in 



(lie lamprey forms a eul-de-- 



