FLAT-FISHES 83 



lobe of tlio same type. It has also been noted that the surface- 

 feeding iishos have small facial lobes. It has been suggested by 

 some writers that a large central acoustic lobe may be associated 

 with the regulation of the gaseous pressm-e in the swim-bladder, 

 but inasmuch as the sole has no swim-bladder in the adult this 

 theory receives no support in its case. Moreover, the gurnard, 

 a bottom -feeding fish with a closed swim-bladder, does not need 

 any special control of the pressure in this organ. 



Evidence has been given associating the large central acoustic 

 lobe in both the giu'nard and mullet with the reception of sounds, 

 the former with noises produced by the fish, and the latter with, 

 noises from external sources. The large somatic-sensory lobes,, 

 similar to those seen in the turbot, and the presence of a large swim- 

 bladder in the larval stage of the sole suggest that originally the- 

 sole had pelagic habits at an early evolutionary stage, and that the; 

 bottom habitat is a recent acquisition. 



