COORDINATION AND BEHAVIOR 



555 



glands may affect one another; for example, 

 if the anterior lobe of the pituitary gland is 

 removed, both the testes and ovaries regress 

 and secrete little, if any, of their respective 

 hormones. Furthermore, several of these 

 hormones may have a similar function, or, 

 on the other hand, they may be antagonistic. 

 Only when all are behaving properly is an 

 equilibrium established among the various 

 physiologic processes in the body, so that 

 we feel and react like normal human beings. 



Other chemical coordinators 



It has been pointed out that the amount 

 of carbon dioxide in the blood controls the 

 respiratory center in the brain and hence 

 regulates the rate of breathing. 



Both the force and the rate of the heart 

 beat can be altered, depending on the re- 

 quirements of the body. The rate of the 

 heart beat can be greatly slowed by the 

 presence of a chemical substance, acetyl- 

 choline, while the presence of an adrenalin- 

 like substance, sympathin, will increase its 

 rate and force. Such substances are called 

 neurohumors ( neurohormones ) because 

 they are liberated at nerve endings. Acetyl- 

 choline is given off by the cranio-sacral 

 (parasympathetic) division of the auto- 

 nomic system, and sympathin is liberated by 

 the nerve endings of the thoracolumbar 

 (sympathetic) division of the autonomic 

 nervous system. There is an increasing 

 amount of evidence indicating that the 

 effects of the autonomic nervous system 

 are not brought about directly by nerve im- 

 pulses themselves, but by chemical sub- 

 stances which the impulses cause to be 

 liberated from the nerve endings. These 

 chemical substances from nerve endings, 

 after performing their physiologic functions, 

 are destroyed by enzymes. 



Both electrical and chemical theories 

 have been advanced in order to account for 

 the transmission of impulses across the 

 synapse between neurons. The evidence, as 

 it now stands, is not sufficient to establish 

 beyond reasonable doubt that transmission 



of impulses from one neuron to another is 

 only by a neurohumor substance. The new 

 knowledge of neurohumors, however, is 

 making it necessary to discard many old 

 concepts of the coordinating mechanism 

 in animals. 



ANIMAL BEHAVIOR 



We have defined behavior as the reactions 

 of the whole organism to its environment 

 and have described the behavior of the 

 amoeba, euglena, paramecium, hydra, earth- 

 worm, crayfish, and frog. The behavior of 

 all these animals has much in common. In 

 the first place, as already noted, one of the 

 fundamental properties of protoplasm is its 

 irritability or ability to respond to stimuli, 

 that is, to react to changes in the environ- 

 ment. 



Protozoans 



The behavior of such simple animals as 

 the amoeba is based on the inherent re- 

 sponsiveness of the protoplasm of a single 

 cell. Such primitive behavior patterns would 

 not make possible the active lives of more 

 complex animals. Even among protozoans, 

 as in the paramecium, organelles involving 

 fibrillar conduction serve to coordinate the 

 activities of different parts of the cell. 



Extensive studies indicate that there is 

 no evidence of the existence of differences 

 of fundamental character between the be- 

 havior of protozoans and that of the lower 

 metazoans. The study of behavior lends no 

 support to the view that the life activities 

 are of an essentially different nature in pro- 

 tozoans and metazoans. The behavior of pro- 

 tozoans appears to be no more and no less 

 machinelike than that of the metazoans; 

 similar principles govern both. 



Sponges 



Sponges are active when in the larval 

 stage, swimming about by means of flagella; 



