62 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
concerned, they were in no observable respect to be distinguished from normal fishes. 
Their rheotaxis certainly did not depend upon their lateral-line organs, but was 
undoubtedly the result of cutaneous stimulation. Unfortunately I was unable so 
to operate on other individuals that I could obtain active specimens whose cutaneous 
nerves were severed but whose lateral-line systems were intact, and hence the only 
conclusion I can draw is that the general cutaneous nerves are stimulated by wave 
and current action and that this is sufficient to account for rheotaxis, but I can not 
state whether or not the lateral-line organs are also stimulated by these means. 
Conclusions concerning the lateral-line organs and the skin. — The observations 
on Fundulus recorded in the preceding pages give no support to the view of P. and 
F. Sarasin that the lateral-line organs are to be regarded as accessory ears, for 
individuals in which the eighth nerves had been cut and in which the lateral-line 
organs were intact did not respond to the sound-waves from a tuning-fork to which 
fishes with ears reacted with certainty. I have also seen no reason to suppose that 
the lateral-line organs are especially connected with the production of gas in the 
air-bladder, as suggested by Richard, or that they are particularly concerned with 
equilibration, as advocated by Lee. Since they are stimulated by slight disturbances 
in the water that do not affect the general cutaneous sense organs, I can not agree 
with Merkel in classing them as tactile organs. Their appropriate stimulus is a 
slight mass-movement of the water, which may or may not be vibratory, and which 
induces the fish to swim into deeper regions. This form of stimulus is of precisely 
the kin d that was attributed to these organs by Schulze (1870), but I have not been 
able to confirm Schulze’s further opinion that current and surface wave movements 
stimulate these parts. Such stimuli certainly do affect the general cutaneous sense 
organs, but whether or not they influence the lateral-line organs I am unable to say. 
GENERAL REACTIONS OF OTHER FISHES. 
Although my studies were made almost exclusively on Fundulus heteroclitus, I 
tested, as opportunities offered, other species of common fishes. These were placed 
without being operated upon in the aquarium with the bass-viol string as a means 
of producing sound. Because of the mixed character of the stimulus produced by 
this apparatus and also because of the fact that the fishes were not operated upon 
in any way, the results are significant in only one or two instances. 
Young mackerel, while swimming in the aquarium, always moved downward 
when the string was vibrated. The same was found true of adult mackerel, but 
whether this reaction was an ear or a lateral-line response was not determined. 
Menhaden, after they became somewhat accustomed to the aquarium, gave a 
sudden leap each time the string vibrated, but showed no tendency to descend. In 
tins instance, too, no clew was obtained as to the organs stimulated. 
Three specimens of smooth dog-fish, each about 18 inches long, were tested. 
When these fish were resting quietly on the stone bottom of the aquarium, the 
vibration of the string would cause them to move their pectoral and pelvic fins, 
or even begin swimming, but when they rested on some 3 inches of cotton wool 
covered with a cloth to afford a deadened surface on the bottom of the aquarium, 
no reaction of any kind was ever obtained. Apparently the ears, lateral-line 
organs, and skins of these fishes are not open to any of the stimuli produced by the 
vibrations of the bass-viol string and transmitted through the water, and they thus 
differ markedly from the other fishes examined. 
