BIOPSYCHOLOGICAL 633 



distinctly experimental, not engrained, character, we would include 

 an exceedingly interesting kind of tentative behaviour, which 

 might, perhaps, be called experimenting below the level of intelli- 

 gence. It is well illustrated by the way in which some individual 

 starfishes, of the common Aster ias rubens species, will tackle small 

 sea-urchins and disarm them by wrenching off the scores of snapping 

 blades or pedicellariae. This remarkable operation is not rewarded 

 until it is completed; it is far from being on the line of least resis- 

 tance ; it is strangely circuitous, for the starfish uses one arm after 

 another; it is an individual activity, not often observed; and it is 

 exhibited by an animal which has no nerve-ganglia in the ordinary 

 sense. The starfish's nervous system consists of a pentagonal ring 

 of simple neurons around the mouth, a strand of the same up each 

 arm, and a loose network of similar cells in various parts of the 

 body, for the most part not sunk in below the surface of the epi- 

 dermis. The same puzzle occurs when starfishes "learn" to right 

 themselves more and more rapidly when they are turned upside 

 down, or "learn" to escape from staples and curved pegs that bind 

 them down. It seems very difficult to think of such cases as illus- 

 trating purely physiological reaction and enregistration. 



CONDITIONED REFLEXES.— The appearance of a translation of 

 Prof. I. P. Pavlov's Conditioned Reflexes has made available a mass of 

 experimental data, hitherto almost unobtainable by students outside 

 Russia, in the field which that great physiologist has made his own. 

 Certainly, Pavlov was not the first to see how artificial was the 

 boundary which separated those activities of the nervous system 

 which were regarded as falling within the province of physiology 

 from those higher faculties which were approached in a different 

 spirit and with the terms and methods of psychology ; but he was 

 the first to plan and carry out a campaign for advancing the frontier 

 of physiology in this direction. 



The simple reflexes, which Pavlov calls "unconditioned", are 

 common to all normal members of a species ; they do not have to be 

 learned, but are inborn. If a man is sitting with one leg over the other 

 and the foot swinging freely, a sharp tap below the knee-cap will 

 cause the foot to jerk upwards as the leg straightens. This is one of 

 the simplest reflexes; it does not require the intervention of the 

 brain; the nervous impulse travels up a sensory nerve-fibre from 

 the "receptor" in the skin to the spinal cord, along a short connective 

 link within the cord, and down another fibre, a motor, to the muscles 

 which cause the leg to straighten. Normally, of course, a message 

 also goes to the brain to report the occurrence ; but the brain does 

 not enter into this simple "reflex arc". By an effort of the will, 

 however, we can, if forewarned, prevent the straightening of the 

 leg and suppress the reflex. 



