THE COD FAMILY 281 



III. Species in which there is no separate first dorsal, but the 

 front part of the single dorsal is a narrow fringe kept vibrating 

 during life. 



14. The Three -bearded Rockling. Two barbels on the 

 upper lip, one on the chin. Marked in the full-grown 

 state with black or brown round spots. 



15. The Pour-bearded Rockling. 



1 6. The Five-bearded Rockling. 



IV. Species in which there is one long dorsal fin and one 

 ventral. 

 17. The Torsk or Tusk. 



long ventral. 



Amongst these, those kinds which are provided with a single 

 barbel on the chin feed chiefly on the bottom, their habit being 

 to swim with their heads inclined to the ground, continually 

 feeling the latter with the barbel. These fish eat both fish and 

 lower animals, especially Crustacea. The ling is an exception, 

 it has a long barbel but feeds almost entirely on active fish. 

 The explanation of this seems to be that the ling is a some- 

 what nocturnal fish which haunts rocky ground and conceals 

 itself in the clefts and holes of the rocks. Its habits pro- 

 bably resemble those of the conger and rocklings, and its barbel 

 is of use to it as a sensitive tentacle to feel its way about, and 

 not to find Crustacea or other animals on the ground. Its 

 elongated shape corresponds to the habit of concealment. The 

 ling is not taken in the trawl so commonly and in such large 

 numbers as the cod is. 



The habits of the rockling are known from observations on 

 specimens in confinement and on the shore. They are entirely 

 nocturnal and self-concealing fish, remaining under stones or in 

 crevices among rocks except when they perceive the neighbour- 

 hood of prey or food, the presence of which they recognise by 

 smell rather than sight. They use their barbels for feeling about 

 on the bottom when seeking their food. 



Those fishes of this family which have no barbel feed more 

 on swimming creatures than on those that walk or crawl, and 

 the kinds that prey most largely on migratory fish which swim 

 near the surface are those which have a projecting lower jaw. 

 This is the case particularly in the pollack, to a less degree in the 



