ADAPTATIONS 395 



also the fifth and seventh nerves supplying the similar organs 

 on the head, and then to compare the behaviour of fishes so 

 treated with uninjured specimens. Only one kind of stimuli 

 were found to produce definite effects which were wanting in 

 the fishes in which the nerves had been cut as described ; these 

 stimuli were vibrations of low frequency produced by pulling 

 the aquarium slightly to one side and then letting it go. The 

 rate of vibration was about six per second. Normal specimens 

 of Fundulus when put into the aquarium swim first to the 

 bottom, and after a time when they have become accustomed 

 to their new surroundings they ascend to the surface. Any 

 slight disturbance such as a quick movement of the observer or 

 a slight jar to the aquarium causes them to descend to the 

 bottom. The slow vibration above described has always the 

 same effect. Specimens in which the nerves to the lateral line 

 organs have been cut, on the other hand, take no notice of such 

 vibrations, although they were sensitive to ripples on the actual 

 surface. Similar reactions to the same kind of vibrations were 

 observed in the other species of fishes tested. 



On the other hand, it was proved that the lateral line organs 

 were not sensitive to sound vibrations although the ears were. 

 It has often been suggested that the lateral line organs are sti- 

 mulated by currents in the water. All the fishes above men- 

 tioned in the normal condition were found to turn their heads 

 always towards the direction of the current, but they did this 

 with equal certainty after the nerves to the lateral line organs 

 had been cut, so that apparently the reaction to the stimulus of 

 a current of water depends on the ordinary tactile sensibility of 

 the skin. The most important question arising from these ex- 

 periments is : what are the stimuli which affect the organs in the 

 natural life of the fish, and this question is not very satisfactorily 

 answered by Parker. He found that when he produced strong 

 ripples on the surface of the water by blowing upon it specimens 

 of Fundulus invariably went to the bottom, while those whose 

 nerves were cut only sank below the superficial water. Still 

 more distinct was the reaction when an object unseen by the 

 fish was dropped into the water. It seems to me from this 

 that the chief use of the lateral line organs is to perceive the 

 movements of other fish in the water. We do not know at 

 present to what distance vibrations due to such movements 



