336 THE BODY AT WORK 



the heaving floor (we speak from personal experience) may result 

 in a heavy fall. Although this phenomenon must be classed 

 with other " after-sensations," it is so prolonged as to suggest 

 that consciousness, having become accustomed to a world 

 which causes a backward and forward flow of endolymph, 

 misinterprets the absence of sensation as indicative of change. 



Taste is, practically, a special kind of smell. A fish's olfactory 

 membrane, taste-buds, and chemical organs "of the lateral line" 

 serve the same sense, although, no doubt, they are applicable 

 to the analysis of different forms of matter in solution. 



Our ideal prevertebrate has now left its primitive undiffer- 

 entiated condition. In front of its mouth it bears organs with 

 which it searches the world. Close behind the mouth are its 

 auditory and orienting organs. The rest of the surface of the 

 body is endowed with the capacity of recognizing " taste," 

 temperature, and contact. Smell, sight, and orientation de- 

 termine the development of the brain. 



The cerebrum which has eventually become, as the seat of 

 consciousness, and hence the apparatus of mind, the dominant 

 factor in the nervous system, was in the first instance the part 

 of the brain concerned with the distribution to the muscles 

 of impulses generated in olfactory organs. There is scarcely 

 any indication in a fish's brain of the representation in the 

 cerebral hemispheres of any other sense, even that of vision. 



A bird's brain presents a striking contrast to the brain of a 

 fish. With the exception of the apteryx and other ground- 

 birds of New Zealand, all birds are apparently destitute of the 

 sense of smell. Vision is the sense upon which their activity 

 depends. It has invaded the cerebrum, converting it into an 

 organ in which sensations of sight are worked up into " mind- 

 stuff." The optic lobe connection is restricted to the produc- 

 tion of reflex actions in which vision is immediately followed 

 by movement. 



All the senses are represented in the great brains of mammals. 

 The cerebrum, which owes its existence to its connection with 

 the favourably-situated sense-organ of the nose, and grew in 

 importance when vision invaded it, has now taken in the senses 

 of hearing, taste, and touch. Only what may be termed in 

 general visceral sense, and the sense of orientation, are excluded. 



Looking back to the starting-point, we see a segmented 



