STRUCTURE OF MYXINE. 403 



fishes, boring its way into them, but the evidence is not 

 satisfactory. J. T. Cunningham discovered that the young 

 animals are hermaphrodite, containing immature ova and 

 ripe spermatozoa, while older forms produce ova only. 

 Nansen has corroborated this, and calls the hag " protandric," 

 i.e., first male and then female. Of the development and early 

 history nothing is known. They are said to spawn in late 

 autumn. 



Form. — The body is eel-like, and measures about fifteen 

 inches when full-grown. There is a slight median fin around 

 the tail; beside the mouth and nostrils are four pairs of 

 barbules or tentacles. There are no paired fins. 



The Skin is scaleless, and rich in goblet cells which secrete 

 so much mucus that the ancients said the hag " could turn 

 water into glue." There is a double row of glandular pits 

 on each side of the ventral surface along the entire length of 

 the animal. Each opens by a distinct pore. 



Muscular System. — The muscle-segments or myomeres 

 are to some extent traceable. Working the rasping teeth is 

 a powerful muscular structure or "tongue." 



The Skeleton is wholly cartilaginous. The notochord 

 persists unsegmented within a firm sheath, the skull is a 

 simple unroofed trough, jaws are not distinctly developed, 

 there is little trace of the complicated basket-work of cartil- 

 age which supports the gill-pouches in the lamprey, but the 

 tongue, the barbules, etc., are supported by cartilaginous 

 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; the fore-brain seems to agree with 

 that of Ganoids and Teleosteans in having a non-nervous 

 roof. The spinal cord is somewhat flattened. Through- 

 out at least a portion of the cord there are two posterior 

 roots for each anterior root. The union of anterior and 

 posterior roots is only partial, and there is no sympathetic 

 system. 



The eye is degenerate {e.g., without a lens or iris), and is 

 hidden beneath the skin ; the ear has only one semi-circular 

 canal ; the single nasal sac opens dorsally at the apex of the 

 head, and communicates posteriorly with the pharynx by a 

 naso-palatine duct. The absence of sensory structures in 



