FUNCTION OF LATERAL-LINK ORGANS IN E'ISHES. 203 



brought into strong contrast the histological differences between the organs of tht> 

 car and the lateral-line system and those of the sense of taste, a contrast strengthened 

 by the recent work of Herrick (1903a, L903b, 1903c). 



The innervation of the lateral-line organs and of the ear also supports the belief 

 in the genetic relations of these parts. Mayser (1881, p. 311) first pointed out the 

 interesting fact that the nerves from the lateral-line organs and from the ear all 

 terminate in one central structure, the so-called tuberculum acusticum, and this 

 observation has been continued and its significance admitted by almost all subsequent 

 investigators. 



The development of the ear and of the lateral-line organs has led to still more 

 important results, however, for in this way it has been shown that both sets of 

 organs are derived from the skin, and that the relations of the ear to the lateral-line 

 organs are such that, as Beard (1884, p. 143) declared, the ear may be regarded as 

 a modified part of the lateral-line system. This opinion was accepted by Ayers 

 (1892, p. 306) in his interpretation of the -work of Allis (1889), and has been main- 

 tained recently by Cole (1898, p. 197) as now 7 fully established, notwithstanding 

 the fact that in some fishes, like Amia, the ear and lateral-line organs develop 

 separately (Beckwith, 1902). 



Finally, the physiological evidence shows that these organs are intermediate in 

 character between the skin and the ear, and support the conclusion elsewhere 

 expressed (Parker. 1903b, p. 198), that together these sense organs represent what 

 may be figuratively spoken of as three generations, in that the skin represents the 

 first generation, which gave rise to the lateral-line organs, from which in turn came 

 the ear. Thus the organs of touch, of the lateral-line system, and of the ear form a 

 natural group, genetically connected as just indicated. 



It may well be asked what disturbances in the water under natural conditions 

 give rise to stimuli for the lateral-line organs. To determine this I tried some 

 experiments with normal and cut Fundulus heteroclitus. It seemed to me probable, 

 since- the vibratory stimulus for the lateral-line organs was usually accompanied by 

 ripples on the surface of the water, that by blowing on the water and producing 

 strong ripples a movement might be induced in the deeper water sufficient to stimu- 

 late the lateral-line organs. This was tested by putting normal fish one at a time in 

 an aquarium about a foot deep and blowing on the surface of the water till strong 

 ripples were produced. All the fishes invariably went to the bottom and stayed 

 there while the wafer remained agitated. These tishes were then cut, and after 

 recovery again tested. While none of them would stay in the superficial water 

 obviously in motion, as, in fact, was to be expected, none sought the bottom as they 

 formerly had. done, and there was no doubt left in my mind that when wind blows 

 upon the surface of water it causes a motion of the deeper water, which stimulates 

 the lateral-line organs. If this be true it follows that the more active fishes should 

 have better developed lateral-line organs than the more sluggish bottom ones, and, 

 at least so far as sharks and rays are concerned, this has been claimed to be so by 

 Garman (1888, p. 65) and by Ewart (1892, p. 81). 



I also tried the effects on normal and cut Fundulus heteroclitus of dropping 

 unseen objects into the water. This was done with as little noise as possible, and 

 almost always was followed by a sudden spring on the part of a normal fish generally 



