90 VERTEBRATE ZOOLOGY 



remains. It seems unlikely that they attack living active prey, as do 

 the lampreys, but they undoubtedly do prey upon fishes caught in 

 gill-nets or upon trot-lines. On account of these habits the hags have 

 acquired a well-earned unpopularity among the fishermen of the 

 North Sea and elsewhere. The flesh of the prey is shredded by means 

 of the strong rasping apparatus, and the digestive tract is so capa- 

 cious that one good meal lasts some time. All active hunting is done 

 at night, for the hags are blind; the day is spent buried in the mud of 

 the sea bottom at depths around three hundred fathoms, where they 

 are themselves safe from enemies. They swim swiftly with an eel-like, 

 undulatory motion. When caught they secrete from the skin glands a 

 great quantity of gelatinous mucus. Hags are said to be the only verte- 

 brates that are specifically hermaphroditic. This character may be 

 associated with their solitary life and with the fact that they are blind. 

 Some of the anatomical characters of the myxinoids that differ 

 from those of the petromyzonts are herewith listed. These charac- 

 ters are illustrated in Figs. 47 and 48. 



I. The mouth is terminal and there is no real buccal funnel. 



2: The naso-pituitary sac (nasal passage and infundibulum) opens 

 into the pharynx and through it water is drawn into the gills while 

 the mouth is engaged in feeding. 



3. There are four pairs of tentacles surrounding the mouth and the 

 terminal nasal opening, which have been compared with the oral 

 tentacles of Amphioxus. 



4. The branchial skeleton (basket) is poorly developed, since it 

 does not have to withstand strong suction. 



5. Dorsal arcualia (vertebral arches) are confined to the tail region 

 or extend only slightly forward from the tail. 



6. No spiral valve in the intestine. 



7. There is a row of mucous sacs on each side. 



8. The brain has no distinct cerebrum or cerebellum. 



9. The eyes are degenerate and without muscles or nerves. 



10. There is no regional specialization of the median fin. 



II. There is only one semicircular canal in the inner ear. 



12. The tongue apparatus is larger and more elaborate than in the 

 lampreys and this pushes the gill-slits further back. 



13. Some of the myxinoids have a larger number of gill-slits than 

 the lampreys, which is considered a primitive character. 



14. The pronephros (larval kidney) functions in the adult. 



