The Sea Lamprey. 41 7 



The sea lamprey (Petromyzon marinus) is specifically dis- 

 tinguished by having the second dorsal fin separate from the 

 tail, although sometimes in only a small degree. 



The body is long and round, slightly compressed, but more 

 so near the tail, and thus not unlike an eel. When the mouth 

 is closed, the part before the eyes appears somewhat length- 

 ened; but when open it is circular and terminal, so that the 

 fish appears as if the head had been cut off. The rim of what 

 may be termed the under jaw is a little curved, forming a 

 ridge which is edged with sharp points ; on the tongue there is 

 a more solid and firm bed of three teeth, having sharp points ; 

 and above, there is an arch of nine bifid teeth, the middle one 

 lower than the others — in all there are ten bifid teeth ; the re- 

 mainder of the mouth is covered with teeth having sharp 

 points, which stand in rows that pass off in curved radii from 

 the throat ; the lower ones small : altogether a formidable 

 arrangement. These teeth are deciduous, the new ones thrust- 

 ing off the old and taking their place. The mode of arrange- 

 ment is a specific character of this fish, and I have found the 

 renewal occurring in May; but it does not appear to observe 

 a regular recurrence. The mouth is fringed with fibres. Eye 

 moderate, lively ; vent far behind. First dorsal fin behind the 

 middle of the body, lower and shorter than the second ; the 

 caudal fin separate, and surrounding the tail. The colour is 

 often variegated and beautiful, as it is referred to by Ausonius ; 

 but sometimes it is plain and almost uniform ;' and this dif- 

 ference appears to belong to the district in which the indi- 

 vidual is found ; but on the whole the tendency is to blue 

 or green, with yellow on the sides and belly. The manner 

 in which the process of breathing is conducted is deserving 

 of notice. Under ordinary circumstances, when the mouth 

 is open, the water probably enters by it and passes out by 

 the openings of the gills; as it does also when the mouth 

 is held above the water, and water is seen to be drawn in by 

 the opening on the head. But on some occasions when wholly 

 immersed it was discharged by that opening as well as by the 

 gills ; but it was never seen to enter by the gills of one side, as 

 has been supposed, to be discharged by the orifices on the 

 other side. This family of fishes has usually been arranged 

 with cartilaginous fishes, which certainly is not its place. They 

 bear a closer affinity to the annelid or worm tribe. Professor 

 Owen says that in their fully ossified skeleton there is only one 

 and a-half of earthy salt per cent. ; and the remainder is 

 mucus, not p-elatine. 



