LAMPREYS AND HAG-FISHES. 525 



situated a considerable distance behind the head, instead of close to it. 

 The eggs difl'er from those of the lampreys by their relatively large size, as 

 well as by having a horny coating furnished with tendrils for the purpose of 

 attachment to submerged objects. The young are hatched in a fully- 

 developed state, and undergo no metamorphosis. In the members of the 

 typical genus Myxiiic there is only one gill-aperture on each side of the body, 

 but this gives rise to six ducts leading to the gill-pouches. On the other 

 hand, in the genus Bdellostoma each of the six or more gill-pouches com- 

 municates directly with the exterior by a separate aperture. Whereas the 

 members of the first genus have a wide geographical range, the two repre- 

 sentatives of the second appear to be confined to the coasts of the South 

 Pacific. All are exclusively marine, and they have been taken at great 

 depths. They are blind, and to a large extent parasitic, so that they may be 

 regarded as degraded types ; and they have the habit of secreting a vast 

 quantity of stiff slime. Like the lampreys, they feed on the flesh of fishes, 

 the various members of the cod tribe being their especial favourites. They 

 do not, however, content themselves by hanging on to the surface of the body, 

 for which the structure of the mouth is less suited, but actually bore their 

 way into the flesh of their unwilling hosts. 



