THE PHYSIOLOGICAL ASPECT 299 
Limulus, when the nerve-chain is severed just in front of the 
abdominal region, the rhythmic respiratory movements of the 
abdominal segments still proceed regularly and co-ordinately. 
Even when only a fraction of the nerve-cord, separated by 
severances in front and behind, is left, corresponding with a 
single abdominal segment, the rhythmic action of that segment 
continues ; but it is no longer synchronous with that of 
adjacent segments similarly isolated. 
It will probably not be contended that the co-ordinated 
rhythm of the isolated seement in crayfish or king-crab is any- 
thing but a bit of organic and physiological behaviour. 
Whether it be accompanied by consciousness—a bit of con- 
sciousness isolated from other bits—we do not know; but we 
have no grounds for supposing that the rhythmic behaviour is 
guided by consciousness. And when, as Dr. Carpenter pointed 
out half a century ago, a water-beetle, from which the ‘“ brain ” 
has been removed, swims forwards if placed in water, we must 
surely regard the co-ordinated progression as organic behaviour, 
whatever view we may hold with regard to a consciousness 
which in such a case is in a very literal sense a divided 
consciousness. 
In these invertebrates the central nervous system is obviously 
segmented—one can distinguish the ganglia and their con- 
necting nerve-strands. In the vertebrate the brain and spinal 
cord form a continuous mass of nerve-tissue without obvious 
segmentation. But the pairs of spinal nerves, each nerve with 
its afferent and efferent ‘‘root,” indicate a really segmented 
condition, though in the cord itself the segments so run 
together and overlap that they cease to be externally obvious. 
And there is a certain, though limited, amount of overlap in 
the distribution of these segmental nerves. Still, well co- 
ordinated responses occur when comparatively short portions 
of the spinal cord are isolated by severance from the rest. In 
the male frog, especially during the breeding season, a clasping 
reflex is produced by stimulating the dark swollen pads on the 
inner side of the hand, and this, as Goltz has shown, is 
exhibited when all the central nervous system has been destroyed 
