S6 BRAIN AND BODY OF FISH 



■cerebellum is moderate in size. The somatic-sensory lobes are more 

 prominent than in the plaice, in fact they approach the form 

 described in the sole. The vagal lobes are small. In the witch, 

 the primitive end-brain is slightly twisted, and the optic lobes are 

 smaller than in the plaice and lemon sole. The somatic -sensory 

 lobes and vagals are similar to those of the plaice, but sections show 

 that the former project more dorsally : the facial lobes are very 

 similar to those of the plaice, but are smaller and produce no bulge 

 into the wall of the rhomboid fossa. The optic lobes are well 

 developed. 



The brain of the dab is like that of the witch but smaller. The 

 most striking feature of the brain pattern of this group is the size 

 of the optic lobes. These, in the plaice and lemon sole, have also 

 their peculiar characters. This is no doubt due to the importance 

 of sight in the hunting habits of these fishes. But it must be remem- 

 bered that this group is well known for its mastery of the art of 

 camouflage. It is true that the protective coloration in fish is 

 controlled by vision, which acts on the pigment cells, caUed chroma- 

 tophores, through the medium of the network of nerve fibres that 

 surround these ceUs. Flat-fishes have also the power of protruding 

 their eyes to a remarkable extent, particularly is this the case in 

 the fish we are now considering. It is assumed that it is necessary 

 for the fish to survey the ground before it can be able to simulate its 

 colour and pattern. Flat-fishes are peculiar in possessing an accesory 

 organ the recessus orbitalis, the function of which is to make the 

 protrusion possible. 



The second feature to be discussed in Group II is the presence 

 of a well-marked facial lobe which is associated with the presence 

 of taste-buds on the Hps and, therefore, indicates an important 

 gustatory mechanism. At the same time it must be noticed that 

 there is no central acoustic area in those fishes of the group that we 

 liave examined by serial sections. We are now in a position to 

 learn what are the dominant special senses that make the hunting 

 equipment of the group. They are, I, sight ; II, taste or gustation ; 

 And lastly, smell. Audition takes no part. The marked difference 

 of this picture from that of the sole is striking and it is not siu'prising 

 that the sole is placed by systematists in a different genus. But 

 there are other differences that may be mentioned namely, the 

 character of the eggs. The eggs of the great majority of flat-fishes 

 are buoyant and pelagic. Those of the sole have a number of small 

 oil-globules at the surface of the yolk, but in aU the members of the 

 families, Bothidae and Pleuronectid£e, the oil-globule is either single 

 or absent altogether, while the plaice has an undivided yolk without 



