MECHANORECEPTORS AND BEHAVIOR 371 



may actually decrease. Ten Kate (1934) showed that these reflexes were 

 initiated and controlled from within one body segment. 



The Labyrinth in Equilibrium 



Because of their accessible labyrinths, because of their hardiness, and be- 

 cause of the simplicity of their behavioural responses, the elasmobranchs 

 were favoured experimental animals in early studies on labyrinth function. 

 The range of experiments performed in several elasmobranch species and the 

 significance of the results of the work of Loeb, Lee, Lyon, Kriedl, and 

 himself are reviewed by Maxwell (1923) in his book Labyrinth and 

 Equilibrium. 



When the body of a shark is rotated (as in "roll") the eyes rotate to 

 preserve the original visual field and the pectoral fins move to restore the 

 body's position. Thus, if the body moves down on the right, the right eye 

 will move up and the left eye will roll down, but the right pectoral fin will 

 move down and the left will come up. These compensating movements, 

 which show the interrelationships between the eye, fin movements and laby- 

 rinth position, require labyrinthine measurements of out-of-true positions. 



The fin movements are to be interpreted in relation to the role of the fins 

 in locomotion, for most elasmobranchs are denser than seawater and need to 

 set their pectoral fins with sufficient angle of attack to generate the correct 

 dynamic lift (Harris 1936). Measurement of the body's relevant angles is 

 presumably done by the labyrinth. 



Harris (1965) has described the movements of the eyes of swimming 

 dogfish and related these to labyrinth function. He found that the eye move- 

 ments of swimming dogfish (Squalus) did not fully compensate for the 

 lateral movements of the head that occur during swimming; the head moved 

 through an arc of about 25°, but the eyes moved backwards only 15°. He 

 analysed these movements into a number of components and found that a 

 free-swimming dogfish with intact labyrinths, but with the spinal cord cut 

 (i.e. a spinal preparation), moved its eyes to obtain complete compensation, 

 whereas in a fish with both eighth nerves cut, but with the spinal cord in 

 connection with the brain, the eyes moved in the opposite sense to com- 

 pensation; the combination of these opposing effects resulted in only partial 

 compensation. Harris pointed out that this would stabilize a visual field on a 

 plane close to the fish, whereas with total compensation the visual field 

 would be stabilised at infinity. 



Destruction of one labyrinth has a pronounced effect, causing movements 

 of fins and eyes, but removal of both labyrinths causes no obvious effect. 

 Surprisingly, fish thus altered swim in what appears to be the normal 

 fashion. 



The Lateral Line in Equilibrium 



One role that it was soon agreed was not the function of the lateral line was 

 an immediate coordination of movement, for lateral-line nerve section had 



