CHAP. XIIL] LOWER ANIMALS. 219 



(previously regarded as one of the parts of the organ of 

 Hearing, of great physiological importance, which he desig- 

 nates the ' sense of Space.' Some of his conclusions on 

 this subject are as follows : 



" The Semi-circular Canals are the peripheral organs of 

 the sense of Space, that is to say, the impressions produced 

 by the excitation of the nerve expansions in the ampulla? 

 of these canals seem to form our notions of the three 

 dimensions of space. The impressions from each canal 

 correspond to one of these dimensions." 



11 The physiological excitation of the peripheric termi- 

 nations belonging to the organ of the sense of Space occurs 

 probably in a mechanical manner, by means of the otoliths 

 which exist in the ampullae. These otoliths will be thrown 

 into vibration by every active or passive movement of the 

 head, and, perhaps, also by the atmospheric waves whose 

 movements the tympanic membrane transmits to the liquid 

 which fills the system of semi-circular canals." 



" The eighth pair of cerebral nerves thus contains two 

 nerves of sense altogether distinct the Auditory Nerve 

 and the Space Nerve (Eaumnerv)."* 



* All that pertains to this difficult subject is still in its infancy. 

 Since the above was in type two articles have been published on 

 the question in this country, which, in addition to exposition and 

 criticism, contain references to the literature of the subject. The 

 one, by Dr. Orum Brown, is in "Nature" for October, 1878; 

 and the other, by Prof. Groom Robertson, in " Mind," October, 

 1878, p. 559. 



