NERVOUS COORDINATION 



CHAPTER 33 



O/l 



Coordination 



and 



Beliavior 



The behavior and reproduction of an ani- 

 mal depend on the coordination of its or- 

 gans. This coordination in the higher 

 invertebrates and vertebrates is accomphshed 

 largely through the agency of a nervous sys- 

 tem and sense organs, and by means of a 

 rxumber of chemical substances (hormones) 

 secreted by the ductless (endocrine) glands. 

 The relations of the nervous system and en- 

 docrine glands are complex and closely asso- 

 ciated. Naturally, the higher an animal is in 

 the scale of life, the more complex these 

 agents of coordination become. We have 

 studied the reactions of a number of differ- 

 ent animals, and their various types of nerv- 

 ous systems, sense organs, hormones, and 

 behavior; now we are ready to consider the 

 subject as a whole. 



Coordination in 

 lower invertebrates 



Irritability and conductivity were found to 

 be fundamental characteristics of proto- 

 plasm. Amoebas and other protozoans that 

 lack specialized organelles for reception of 

 stimuli, nevertheless, respond to changes in 

 the environment much as do higher animals 

 that possess sense organs and nervous sys- 

 tems. However, some of the more complex 

 ciliates are supplied with a system of fibrils 

 (neuromotor apparatus), some of which are 

 conductile, for example, coordination of 

 ciliary action. Reactions to stimuli in 

 sponges are hardly more advanced than in 

 protozoans, unless the studies of deCeccatty 

 prove to be correct. If the researches going 

 on now in America confirm deCecatty's 

 report of a primitive type of nervous system 

 in sponges, then it will be recognized that 

 true nerve cells first appear in sponges rather 

 than in the hydra (coelenterate). However, 

 if no nerve cells are present, then stimuli are 

 transmitted very slowly from cell to cell. 

 True nerve cells unquestionably appear in 

 the hydra, where sensory cells (receptors) 



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