128 OTOLITH ORGANS AND SEMICIRCULAR CANALS 



that the compensatory motions described in the case of animals 

 from which all the ampullae have been removed occur also when 

 activity of the retina has been excluded. 



It must also be noted that the dogfish, Hke most animals which 

 rest on the bottom and are not merely suspended in the water, mani- 

 fests very strong contact reactions. A vigorous specimen which has 

 been bhnded and which has had as far as possible all the end organs 

 of the eighth nerve destroyed will almost always be found belly 

 down when at rest. Such a fish may swim indifferently back or belly 

 up, but when it comes to rest the position is a fair index of the general 

 state of the animal. When an investigator affirms that his specimen 

 came to rest indifferently in any position, he has given good incidental 

 evidence as to the animal's physical condition. In stating that a 

 dogfish deprived of its six ampullae makes normal righting reactions 

 I have not been unmindful of these facts, but have taken care to 

 exclude the possibihty of contact stimuli. 



Although it can be proved that after the loss of all the ampullae, 

 with exclusion at the same time of retinal and contact stimuH, the 

 dogfish makes normal compensatory movements of the eyes and fins 

 to rotations in all vertical planes, it is necessary to note that there 

 are some differences between this and a normal animal. 



The following seem to be fairly constant results. (1) The com- 

 pensatory movements of the eyes, though prompt, are noticeably 

 slower than in the uninjured animal. Compensatory movements 

 due to visual stimuli alone are so much slower, requiring several 

 seconds or even minutes, that no difficulty is experienced in distin- 

 guishing these from reflexes of labyrinthine origin. (2) If seized 

 while in the water the animal strongly resists the attempt to turn 

 it back downward. One feels, however, that the resistance is neither 

 as prompt nor as strong as in a normal animal. (3) In swimming 

 there is more or less evident a slight tendency to sway from side to 

 side around the longitudinal axis, Hke a boat insufficiently ballasted. 



These three conditions are less noticeable in vigorous specimens; 

 they become very marked in weakened individuals. They can per- 

 haps all be accounted for by a lowering of muscle tonus. It is impor- 

 tant to note that, as I shall show later, precisely the same complex 

 of conditions can be brought about through a totally different 

 operation. 



