702 Comparative Morphology of Chordates 



sustain great weight. Accordingly, it consists of a large number of 

 strands of wire. A telephone or telegraph cable contains many wires, 

 each wire (or pair of wires) serving a particular instrument or group of 

 instruments. The single and simple weight-supporting function of the 

 bridge cable is the summation of the functions of its many constituent 

 wires acting all at once and all in the same way. The electric cable, as a 

 whole, may be said to perform the function of communication, but it 

 does not act as a whole in the manner that the bridge cable does. 

 " Communication" is not the mechanical resultant of the actions of its 

 wires acting all at once and all in the same way. Its specific functioning 

 is that of the individual wire. The many wires act independently. 

 They do many different things and probably they never all act at once. 

 Were they to do so, the summation of their actions would not be a 

 useful function analogous to the supporting function of the bridge 

 cable; it would be a chaos of jumbled messages. 



A muscle, consisting of many parallel muscle-fibers (cells), re- 

 sembles the bridge cable except in that the function of the cable is 

 static and that of the muscle is dynamic. The essential function of the 

 muscle is its contraction, which is the summation of the contractions 

 of its constituent fibers. The brain resembles rather the electric cable. 

 The function of the brain as a whole may be said to be the control of 

 the activities of the animal, but this total function is not the mechanical 

 resultant of the simultaneous action of all of its constituent parts as it 

 is in the bridge cable and muscle. Its essential functioning is that of 

 the individual nervous elements or groups of related elements acting, 

 at a given moment, independently of other elements or groups, the 

 several elements or groups having each its own specific function and 

 never all acting at once. (Were they all to act at once, the result might 

 be cataclysmic for the animal!) 



In muscles, hearts, stomachs, and glands, the function as a whole 

 is the important thing, and each of the organ's constituent cells is 

 functionally, as well as structurally, a subordinate constituent of the 

 whole. In a brain the function of a single cell (neuron) or group of 

 cooperating neurons is the primary thing. There is, in strict sense, no 

 nervous function of the brain as a whole. Its size is, therefore, inci- 

 dental to the necessary number of its neurons, and the form of the 

 whole brain is merely an incident of the necessary and specific arrange- 

 ment of the constituent parts, having in itself no dynamic or physio- 

 logic significance — i.e., it would not matter functionally whether a 

 certain lobe of the brain were spherical, ovoid, or cubical, so long as its 

 constituent neurons were properly connected. In short, then, the larger 

 muscle, contains more cells because its function requires that it be larger: 

 the larger brain is larger because its functions require that it contain more 

 cells. 



