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CHAPTER yill. 



ON PROBLEMATICAL ORGANS OF SENSE. 



In addition to the organs of which I have attempted 

 in the preceding chapters to give some idea, and to 

 those which from their structure we may suppose to 

 perform analogous functions, there are others of con- 

 siderable importance and complexity, which are evi- 

 dently organs of some sense, but the use and purpose 

 of which are still unknown . 



" It is almost impossible," says Gegenbaur,* " to 

 say what is the physiological duty of a number of 

 organs, which are clearly sensory, and are connected 

 with the integument. These enlargements are generally 

 formed by ciliated regions to which a nerve passes, 

 and at which it often forms enlargements. It is 

 doubtful what part of the surrounding medium acts on 

 these organs, and we have to make a somewhat far- 

 fetched analogy to be able to regard them as olfactory 

 organs." 



Among the structures of which the use is still quite 

 uncertain are the muciferous canals of fishes. The 

 skin of fishes, indeed, contains a whole series of organs 

 of whose functions we know little. As regards the 



* " Elements of Comparative Anatomy." 



