ADVANTAGE OF DISTANCE RECEPTORS 157 



ment and is therefore the first to be affected by whatever 

 is new in that environment. Obviously, the receptors at 

 the front end will be most frequently stimulated and their 

 stimulation will be of greatest significance to the or- 

 ganism. It is in accordance with this principle that we 

 find the most important receptors at the front end; and 

 particularly is it true of nearly all animals that such 

 distance receptors as they possess are in that part of the 

 body. An important consequence of this grouping of the 

 distance receptors in one region is the corresponding in- 

 crease in size and complexity of the front ganglia. The 

 distance receptors ar^ complicated organs composed of 

 numerous parts and requiring many sensory nerve-cells 

 to connect them with the central ganglia; the result is 

 that the ganglia at the front end of the body are usually 

 the largest of all that the animal possesses, and on account 

 of their connection with the distance receptors they are 

 also the most important. Here we have the beginning 

 of the brain, namely, a group of ganglia with an especially 

 large number of sensory nerves leading in, and of course 

 an equivalent supply of outgoing nerves, either motor, 

 leading directly to effectors, or connecting, leading to 

 other ganglia, and so, indirectly, to more distant effectors. 

 Moreover, it is of predominating importance because it 

 is the ganglion-group with which all the distance recep- 

 tors communicate and into which, therefore, are poured 

 the nervous impulses bringing information of facts in the 

 environment at a distance from the body surface. These 

 factors of numbers of nerve connections and of relation 

 with the distance receptors, in combination, make the 

 brain at once the dominant part of the nervous system. 

 The Advantage of the Distance Receptors. — When 

 the contact receptors are stimulated, the response is as 

 prompt as the working of the mechanism will permit. 

 Obviously, this promptness is an essential part of adjust- 

 ment to contact stimuli, since if the source of the stimu- 

 lation is in immediate contact with the body immediate 



