384 HAVE FISHES MEMORY. 



lateral line and ■ certain similar apparatuses in the head of sharks are 

 brought into action by no irritations other than those produced by 

 variations in pressure. The ingenious series of experiments by which 

 he arrived at his result deserves special mention. Through every 

 nerve runs a so-called current of action, demonstrable by means of 

 electric appliances. At the moment when a nerve comes into action 

 the intensity of this current is somewhat diminished. Not all irrita- 

 tions produce this result; only such as actually force the nerve into 

 action. For instance, the current of action in the eye is weakened 

 when light falls upon it, not if the eye is excited in some other way. 

 Fuchs measured the current of action in the nerves of the lateral line. 

 He noted a diminution in intensity only when the uninjured fish was 

 exposed to variations in the pressure exerted by the surrounding water. 

 These oscillations, then, are the irritations to which the apparatus in 

 the lateral line responds. 



Let us sum up briefly m hat conclusions may be derived from our 

 data concerning the sense impressions of fishes. They respond to 

 chemical irritations (sense of taste and smell); the}^ receive light sen- 

 sations, gain optical images through their eyes, and can see. It is ques- 

 tionable whether, properly speaking, they can hear, but they are aware 

 of violent commotions in the water, even such as are produced by sound 

 waves. P'inally. it appears that they possess additional sense organs in 

 the canals of the head and along the lateral line which permit sensa- 

 tions corresponding to variations of pressure exerted by the surround- 

 ing medium. With regard to this sense apparatus, we know not only 

 the end organs at the surface of the body, but also the nerves and 

 their termini in the brain. AVe know, furthermore, that not a single 

 one of these nerves extends beyond the first ganglion it reaches, but 

 there are fiber strands which join all these end ganglia to one another 

 in definite, constantly recurring ways. The question now is, Is the 

 above apparatus fitted to retain impressions brought to it ? Is there 

 any lingering effect from past irritations? 



As we have absolutely no knowledge of the psychic processes that 

 fish may undergo — in other words, of states of consciousness accom- 

 panying the various movements visible to us — our descriptions must 

 make use of a nomenclature which, as far as practicable, eschews the 

 terms used for similar processes in man, for in order to keep strictly 

 within the bounds of science we must refuse to entertain any suppo- 

 sition not forced upon us by given phenomena. We shall regard the 

 animal as a machine, but by no manner of means is this attitude to be 

 taken as a prejudgment of psychologic data of which we are still igno- 

 rant. A machine always responds to the touch of a given kej^ or 

 valve with the same motion; the relation between irritation and move- 

 ment is absolutely simple and strictly regulated by law. Such simple 

 relations are not unknown in the animal kingdom. They are charac- 



