150 NERVOUS CORRELATION 



It will be seen that the contact of one with the other is 

 so close that a disturbance of the sensitive cell, to which 

 we may now give the name of receptor since it is special- 

 ized for receiving stimuli, can be transmitted directly to 

 the effector (muscle) cell so as to excite it to activity. 

 The next step in the development is seen in Fig. 40, 

 w^here the receptor at the surface is separated by a short 

 distance from the muscle cell; the gap is bridged by 



Fio. 40. — Diagram illustrating how a projection of sensitive cell, 

 /?, may bridge a small gap to contractile cell, E, enabling a dis- 

 turbance of I{ to 1)0 transmitted across the gap to E. 



an outgrowth of the receptor cell which enables it to 

 establish contact with the effector. The next step, which 

 is illustrated in Fig. 41, is one in which the distance be- 

 tween the receptor and the effector is too great to be 

 briflgofl by a simple extension of the receptor, and so we 

 find another cell making the connection. This cell which 

 comes between the receptor and the effector cells, and 

 serves to carry messages across from the receptSr to the 



