THE REFLEX ARC 245 



gradients or excitation arcs, either local or general or 

 both, and excitation and its transmission occur in proto- 

 plasm where no visible nerve structure exists. 



Finally, the difficulty of conceiving a nervous system 

 without effectors which was pointed out by Samassa 

 and Schaeppi is a real difficulty, but when we remember 

 that primitive protoplasm is effector as well as receptor 

 and conductor and that passage of excitation over any 

 protoplasmic region involves reception, conduction, and 

 effect, this difficulty remains only for the teleological 

 point of view. When we consider the nervous system 

 as an adaptation for biological purposes, its existence 

 without adapted effectors is difficult or impossible to 

 conceive, but when we consider it as the visible expres- 

 sion and record in protoplasm of an excitation gradient 

 or gradients resulting primarily from a differential 

 relation to the external world, the presence or absence 

 of a specialized effector becomes a matter of minor 

 importance. In the first case we are considering the 

 nervous system as a means, and without relation to the 

 end the effector or the effect produced by it it 

 becomes inexplicable, while in the second case we are 

 considering it as an effect or result, and as such it 

 follows necessarily from the irritability of protoplasm, 

 the gradients, the capacity for morphological differen- 

 tiation, etc. 



THE FUNCTIONAL DIRECTION IN THE NERVE NET 



The question of the localization of receptor, con- 

 ductor, and effector and of what may be termed the 

 functional direction of the reflex arc with respect to 

 the axial gradients remains to be considered. As 



