CONFORMITY WITH PLAN 305 



in the Infusoria, which have no digestive organs developed. 

 Here, as we have aheady pointed out, the same food-vacuole 

 goes through all the changes shown by the framework of the 

 alimentary canal of the higher animals. The rhythm of the 

 impulses in the completed organ-chain becomes effective 

 indirectly through a permanent framework, and is directly 

 active only from time to time when that is locally disturbed : 

 in the Infusoria it is expressed directly through a progressive 

 framework-forming. 



If we look into the matter more closely, we shall under- 

 stand why the digestive process so easily gets fixed by 

 permanent framework formation, and becomes frozen into a 

 chain of reflexes. Each stretch of the alimentary canal forms, 

 with the food-ball as indicator, a very simple kind of function- 

 circle, which is shut off as a pure reflex arc in the tissues 

 of the animal. The demands made on the steering-mechanism 

 of the nervous system are very slight. The receptors may 

 everywhere lie close to the glands, and convey the excitation 

 to them by simple nerve nets. The secretion from the 

 stimulated glands alters the food-ball in such a way that, 

 when it gets to the next section, it sends forth other stimuli 

 for which there are other receptors. 



The onward movement of the food-ball is effected by the 

 movement of the circular muscles, according to the simple law 

 of muscular tension. Round the food-baU they are on the 

 stretch, and so the excitation flows ^to them, and they push 

 the ball forward. 



Of course, at each digestive process there occur a number 

 of complications, since the food consists of different sub- 

 stances, which must simultaneously be partially broken down : 

 several function-circles then interlock. But the principle is 

 everywhere the same and everywhere simple. 



If we compare the movement-functions of an animal with 

 those of its digestion, we get the reverse picture. Here the 



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