112 BRAIN AND BODY OF FISH 



facial, somatic in origin, from the fins and the barbels, and dorsal 

 organ. As the sections are traced caudally the facial nerves turn 

 sharply backwards and are seen as a thick trunk entering the facial 

 lobes. This trunk at first lies superficial to each lobe, which seems 

 to be divided into a mesial and lateral portion by some of the fibres 

 of the nerve, the lateral portion being the larger. 



As the nerve loses itself in the substance of the facial lobe this 

 is seen to increase greatly in size, and each lobe, appears in section as 

 a somewhat pear-shaped mass bulging laterally, and ventrally a 

 stalk, composed of descending fibres from the lobe, passes downwards 

 and outwards to enter the great longitudinal secondary gustatory 

 tracts. More posterior still the large mass of the facial lobes appears 

 to be again separated into two divisions, the internal portion ex- 

 tending further caudally than the lateral. In the more posterior 

 sections the motor nuclei of the vagal lobes appear, and dorsal to 

 this the sensory portion of this lobe is seen to pass upwards to occupy 

 the site previously taken by the inner division of the facial lobe. 



We see here a somewhat similar condition to that found in the 

 gudgeon loach and barbel, a division of the facial lobe on either side, 

 and also of the seventh nerve after it enters the brain, corresponding 

 to the elaboration of the gustatory function which results from the 

 varied stimuli received from the different groups of taste-buds. The 

 course of the nerves supplying the dorsal organ have now been 

 traced to the medulla, and it may be assumed to a specialised area 

 of the facial lobe ; there can be little doubt that the vibratile mem- 

 brane of the dorsal fin causes a stream of water to pass along the 

 chink with its collection of taste-buds, and the taint of any prey or 

 food would be recognised by these organs. 



The rockhngs are entirely nocturnal in their habits and remain 

 under stones or in crevices among rocks except when they dart out 

 to seize their prey, which they recognise by smell, but more particu- 

 larly by taste and to a much less extent by sight. The large primitive 

 end-brain points to a well-developed olfactory function and the 

 smajl optic lobes are in keeping with their nocturnal habits. 



