162 BRAIN AND BODY OF FISH 



cod, ling and pollack, with large fifth lobes and, among flatfish, 

 as turbot and particularly the halibut, the same enlargement is 

 present. 



Our task is nearly finished and we return with relief to the 

 seventh or facial nerve and taste-buds. As has been pointed out, 

 these organs apparently subserve different kind of sensory stimuh, 

 which we have called gustatory and "sentinel." The taste-buds, 

 with gustatory function are usually in the front of the mouth and 

 on the lips, and the sentinel in the branchial region and at the 

 entrance of the pneumatic duct into the gullet. 



These groups are supplied by the facial, the glossopharyngeal 

 and the vagal. When taste-buds are also situated on barbels 

 it is found that the nerve fibres from the barbels enter the facial 

 lobe with the fibres from the lips and body, but separate within 

 the lobe, the barbel fibres passing to the posterior part of the lobe. 

 The facial lobe only undergoes great enlargement when there are 

 barbels present. 



In the carps the mud-eating members of the family have a 

 specialised area, carrying taste-buds called the palatal organ, 

 which sifts the mud from the nutriment ; tliis area is supplied by 

 the IX and vagal nerves and is the cause of the great enlargement 

 of the vagal lobes. It is interesting to note how taste-buds may 

 form special taste areas as is seen in the rocklings, which have 

 adapted the dorsal fin to a taste organ. The dorsal fin is adapted 

 in other fish for other purposes besides propulsion and gustation, 

 it becomes a weapon of defence in the weever and a lure in the 

 angler fish ; in the rocklings, however, it causes a great enlargement 

 of the facial lobe. 



The question has not yet been answered, is the adaptation of 

 an organ to a specialised function as the palatal organ, the cause 

 of the increased size of the vagal lobe, or vice versa, does the neces- 

 sity of providing a sorting organ, cause an enlarged vagal to stimulate 

 the formation of a palatal organ ; also how far random variation 

 is responsible for the existence of the palatal organ, and the en- 

 larged vagal. 



It is a matter of common knowledge that, in the liigher verteb- 

 rates, the importance of the special senses vary to a considerable 

 extent. 



In man we all realise how little the sense of smell is developed 

 compared with the conchtion found in the lower animals. This 

 fact is even borne out in the study of language. Logan Pearsall 

 Smith in the appendix to his book, " Words and Idioms," gives 

 a hst of " corporeal " idioms, and points out that the human head 



