COORDINATION 



429 



• - 



salh 



capillary 



capillary 



zmymz 



sweot gland 



digestive gland 



Fig. 16-25. Two different types of glands and how they function. Sweat glands merely extract the substance from 

 the blood, concentrate it, and secrete it. Digestive glands, on the other hand, must manufacture the enzyme from 

 row materials supplied from the blood, and then secrete the finished product. In both instances energy is 

 required. 



the synapse, which would indicate that 

 sometliing happens to them as they pass 

 through the gap. Not only is there a delay 

 in the transmission of the impulse as it 

 passes through the synapse but something 

 happens in this junction which allows the 

 impulse to cross it in only one direction. 

 These characteristics of the synapse may 

 indicate that the neurohumoral explanation 

 is the correct one, although there is more 

 work to be done on the problem before this 

 can be stated positively. 



EFFECTORS-THE ORGANS 

 OF RESPONSE 



The principal effector organs of higher 

 animals are the muscles and glands, al- 

 though there are other types of effectors in 

 use throughout the living world. For ex- 



ample, there are chromatophores, found in 

 a large group of vertebrates and inverte- 

 brates, that are responsible for rapid color 

 change in the skin. Some animals possess 

 luminous organs which radiate light when 

 stimulated and still a few others possess 

 electric organs that generate electrical dis- 

 charges under suitable conditions. Each of 

 these effectors will be discussed briefly with 

 the exception of the muscles which have 

 been treated rather thoroughly in Chapter 

 15. 



Glands 



Skin glands have already been discussed 

 ( Chapter 14 ) but there are other glands in 

 the body which are stimulated directly by 

 the nervous system. Just how a gland cell 

 secretes is not well understood. Its job is 

 to extract the product of secretion from the 



