80 BRAIN AND BODY OF FISH 



We must now mention the existence of a special organ, the well- 

 known papillary area on the lower or left side of the head, an area 

 covered with a number of villi. Bateson has stated that " contrary 

 to expectation these villi do not bear sense organs of the nature of 

 taste-buds," and my own observations confirm this conclusion, 

 although it has been denied by Cunningham ; but it accords with 

 the evidence given above, that the facial lobes are minute. The 

 presence of these villi explain the large size of the somatic-sensory 

 lobes which receive the tactile sensations from these sensory 

 filaments. 



" When searching for food the presence of which it recognises by 

 smell, the sole glides gently about over the sand, tapping with the 

 lower side of the head, in order to bring this sensory area in play. 

 The sole is one of the flat-fishes most addicted to burying themselves 

 in the sand or mud, leaving only the eyes exposed." 



It is commonly held by fishermen in the North Sea that soles 

 not only cover themselves when light is directed upon them but 

 bury themselves during periods of intense cold. Russell states 

 that they take no notice of a worm dangled above them : but Bateson 

 observed " that they perceive objects approaching them, for they 

 will bury themselves if a stroke is made with a landing net," but this 

 might also be exjjlained by vibrations produced by the rapid motion 

 of the net. But soles, eels, and rocklings have a clear appreciation 

 of light and darkness, always being buried during the day and swim- 

 ming about in their tank at night. 



The olfactory system is highly developed in the sole, as will be 

 described later, and the eyes of the sole are small. Not only are 

 the eyes of the sole small but their optic lobes are small in marked 

 contrast with the large optic lobes of the plaice. When we review 

 the above facts it seems possible to formulate a probable theory of 

 the significance of the central acoustic area in the sole. As a general 

 rule a central acoustic area is weU-marked when the facial lobe is 

 small and vice versa, and there is a large amount of evidence avail- 

 able in support of the view that it is associated with an auditory 

 function. How can we explain its presence in the sole ? We 

 suggest that an auditory centre would be of value to the sole, and 

 at least it is a reasonable assumjjtion that this centre is associated 

 with the perception of vibrations. 



The tapping of the sand so characteristic of the sole's method of 

 hunting, reminds one of the thrush feeding on our lawns, tapping 

 and listening for the hidden worm. Sea-birds, such as certain gulls 

 and the sheldrake, tap for worms, in the same way, on our shores 

 and in estuaries. 



