MULTICELLULAR ANIMALS 209 



complex of human behavior commonly called personality is the sum 

 of many characters, including the state of the endocrine glands. 



Transmitted Correlations. The production of a hormonal 

 substance by a gland, its transportation, and its effect are time 

 consuming. For immediate response and rapid unification the 

 organism is equipped with a system for transmitting correlating 

 impulses. The principal agent in transmitted correlation is the 

 nervous system. 



Irritability is one of the fundamental properties of living ma- 

 terial. Irritability in the organism consists of three phases: First, 

 excitation. Thus if the finger is placed on a hot object the heat 

 excites a certain type of specialized nerve tissue. Second, transmis- 

 sion. If only the region in contact with the hot object were excited, 

 there would be no response and the excitation would serve no use- 

 ful purpose. Some sort of influence is propagated along the nerve to 

 ■other tissues. Third, response. The propagated impulse passes along 

 the nerve path until it reaches a muscle, and sets in motion a re- 

 sponse that results in the contraction of the muscle and a conse- 

 quent withdrawal of the finger. Thus in the highly organized 

 irritability mechanism of the human body the necessary structures 

 are: receptor, transmittor, effector, in the order named. But 

 even in the most simple animals these three components are always 

 concerned in any response to an outside stimulus. 



Primitive Excitation-Transmission Systems. We have 

 seen how in certain Protozoa, in the genus Diplodinium for instance, 

 there are definite paths over which pass correlating stimuli, a neuro- 

 motor system. In such forms as the genus Amoeba, however, no spe- 

 cialized system has been detected. We are forced to conclude that in 

 such simple types the properties of receptor, transmittor, and effector 

 are properties of the cell as a whole, with no special differentiations 

 or localizations, except that the surface of the cell must be the locus 

 of reception for all stimuli. In the members of the phylum Porifera, 

 the sponges, the cells that serve to receive and to transmit stimuli 



