MYXINE. 



47 1 



ginous rods. The end of the notochord in the tail is quite 

 straight (protocercal or diphycercal). 



Nervous system. — The brain has the usual parts, but is 

 small and simple. It is much compressed, with practical 

 obliteration of the ventricles. The fore-brain seems to agree 

 with that of Ganoids and Teleosteans in having a non- 

 nervous roof. The cerebellum is particularly small. The 

 spinal cord is somewhat flattened, and is sheltered simply 

 by fibrous tissue. Throughout at least a portion of the 

 cord there are two dorsal roots for each ventral root. The 

 union of dorsal and ventral roots is only partial, and there 

 is no sympathetic system. There is no lateral line system. 



The eye is without lens, cornea, or iris, and is hidden 



Fig. 199.- 



-Median longitudinal section of anterior end 

 of Myxine. — After Retzius. 



N., nostril ; 5., barbule ; p., brain ; nek., notochord ; C, gullet ; TV, tongue 

 muscle ; M., mouth cavity. 



beneath the skin ; the optic nerves do not cross ; the ear 

 has only one semicircular canal. The single nasal sac (with 

 paired folds of olfactory epithelium in Bdellostoma, an 

 American relative) opens dorsally at the apex of the head, 

 and communicates posteriorly with the pharynx by a naso- 

 palatine duct. It may be, as in the lamprey, a combination 

 of. olfactory and pituitary involutions. The absence of 

 pigment and sensory structures in the skin, and the simple 

 state of the eye and ear, may be partly associated with the 

 hag's mode of life, but it seems probable that the simplicity 

 is primitive rather than degenerate. 



Alimentary system. — The mouth is suctorial. There is 

 a median tooth above, and two rows of teeth are borne on 

 each side of the muscular "tongue." These teeth are 



