ON THE MORPHOLOGICAL AND PHYSIOLOGICAL 

 CLASSIFICATION OF THE CUTANEOUS 

 SENSE ORGANS OF FISHES. 



C. JUDSON HERRICK. 



In determining the rank and meaning of any given sense 

 organ there are three criteria to which we may appeal. (i) 

 Doubtless the most important is direct introspective knowledge, 

 the psychological criterion. This criterion obviously is not avail- 

 able to us in the study of the senses of the lower animals, where 

 we are shut up to the remaining two. (2) Of these the most 

 important is direct physiological experimentation. The sense 

 organs under consideration are subjected to various types of 

 stimuli under experimental conditions and the reactions noted — 

 the physiological criterion. (3) The structure of the organs 

 frequently permits of inference as to probable function, a 

 method of small value except as controlled by other data — the 

 anatomical criterion. 



For over two centuries it has been known that the fishes 

 possess various highly specialized sense organs in the skin, and 

 for over half a century it has been recognized that these belong 

 to two distinct morphological types. The problem of the mor- 

 phological and physiological significance of these organs has exer- 

 cised some of the ablest zoologists during the whole of these 

 periods without, however, any agreement having been reached. 

 The reason for this unsatisfactory condition is not far to seek. 

 Most of these authors have been content with inferences as to 

 function based on studies of the structure of the organs — a 

 perilous course at the best — and few carefully wrought out 

 physiological experiments have been made. By the cooperation 

 of a number of students this condition is now largely remedied 

 and positive conclusions become possible. We shall summarize 

 these conclusions without in this place undertaking to give the 

 evidence for them in detail or to cite authorities, taking up first 



