422 FISHES CHAP. 
supplying them have atrophied. The embryonic pronephros is 
retained in the adult. The eggs are large; segmentation is 
meroblastic ; and development is direct, without a larval meta- 
morphosis. Two families can be distinguished. 
Fam. 1. Myxinidae.—Gill-sacs not exceeding six pairs, with 
a common external aperture on each side of the body. 
The family includes a single genus, My«ine, of which the 
common Hag (JZ glutinosa) from the North Atlantic is the best 
known species (Figs. 92, A, and 240). This Hag-Fish occurs 
off the coasts of Northern Europe, including the British Isles, as 
well as on the Atlantic sea-board of North America,’ southwards 
to Cape Cod. Other species are found off the coasts of Chili 
Fic. 240.—Myzine glutinosa. A, lateral view ; B, view of the ventral surface of the 
head, showing the mouth and tentacles. J./.p, Lateral pore-like apertures of the 
mucus-sacs 3 v, anus. 
and Japan. Myaxine is quasi-parasitic in its habits, boring its 
way into the bodies of large Fishes. By means of its rasping 
“tongue” it devours all the soft parts of its prey, leaving little 
more than a mere shell of skin and bones. The Fishes usually 
attacked are the Cod and other Gadoids, but the Sturgeon is not 
immune, and the presence of a Hag in the abdominal cavity of a 
Shark (Zamna cornubica) has been recorded. Myxine has the 
reputation of being very destructive to Fishes caught on lines, 
and it is said that whole “catches” have been destroyed by its 
depredations, so that North Sea fishermen have been forced to 
change their fishing-cround. To what extent the Hags attack 
Fishes which are living and free is somewhat uncertain, but the 
little evidence obtainable seems to point to the conclusion that, 
as a rule, they only prey on Fishes when the latter are hooked or 
netted, or injured or dead. When not seeking food the Hag lives 
1 The American Hags probably belong to a distinct species, M. /imosa Girard ; 
Bashford Dean, Sciénce (N.S.), xvii. 1908, p. 483. 
