CORRELATION IN HIGHER FORMS 151 



effector, constitutes the beginning of a definite adjustor 

 mechanism. 



Correlation in Higher Forms. — As one goes up the 

 animal scale beyond the most primitive multicellular 

 types increased complexity of structure is shown in va- 

 rious directions. Only two are to be stressed here. They 

 are (1) increased number of receptors and effectors, and 

 (2) a device for permitting flexibility of connection be- 



FiG. 41. — Diagram to show how when the distance from R to E 

 is too great to be bridged by a simple outgrowth of R an additional 

 cell, A, establishes the connection. Such an intermediary cell, 

 speciaUzed for conduction, represents the beginning of a definite 

 adjustor mechanism. 



tween the receptors and effectors. In the last paragraph 

 the organism was pictured as though it had only one re- 

 ceptor and one effector, so that the only nervous system 

 required was a single cell connecting the receptor to the 

 effector. As a matter of fact, one does not have to go 

 very far up the animal scale before encountering forms 

 which have many receptors and likewise a goodly number 



