Mammalia: Visceral Systems — 



Respiratory, Circulatory, Alimentary, 

 Urinogenital 



17 



An automobile, a motor ship, and an airplane are very different in 

 form, structure, and general appearance, yet their engines may be 

 very similar. Their ability to operate under the diverse conditions 

 attending motion on land, on water, and in air depends upon differ- 

 ences in the structure of the "bodies" of the several mechanisms and 

 not on the use of totally different types of engine. An animal may run, 

 leap, swim, fly, dig burrows, or climb trees. Each type of activity 

 requires appropriate adaptation of the muscles and skeleton. The 

 requirements are so different that the several bodies may appear to us 

 in the forms of mammals so unlike as a tiger, a mole, a bat, and a 

 whale. But corresponding visceral organs of very different mammals 

 may possess only relatively minor differences. Digestion is the same 

 sort of process whether the animal runs or swims. It makes no differ- 

 ence to a kidney whether the wastes to be eliminated result from mus- 

 cular activities of flying or of burrowing. 



Somatic (referring to the body-wall) anatomic differences between 

 two animals are especially significant because they are directly cor- 

 related with the specific functional adaptation of either animal to its 

 particular mode of living. Therefore somatic differences are to a 

 large extent qualitative. Running, swimming, and burrowing are not 

 just more or less of the same sort of thing. They are of different sorts, 

 each having its peculiar pattern of muscular activity and a correspond- 

 ing anatomic pattern. Visceral differences are to a large extent merely 

 quantitative. The organs of nutrition, respiration, and excretion merely 

 have more or less of their work to do depending on the amount of 

 energy expended by the somatic mechanisms. However, new visceral 



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