ORGANIZATION 243 



tinguish between what is necessary and what is only ac- 

 cessory. That only is essential to life which is common 

 to all forms of life. Our brains, stomachs, livers, hands, 

 and feet are luxuries. They are necessary to make us 

 human, but not living, beings. Half of our body is 

 taken up with a complicated system of digestion ; but 

 the amoeba has neither mouth nor stomach. We have 

 an elaborate apparatus of motion ; the adult oyster can 

 not stir an inch. 



Nutrition, Motion, and Sensation indicate three steps 

 up the grade of life. Thus, the first is the prominent 

 function in the coral, which simply "vegetates," the 

 powers of moving and feeling being very feeble. In 

 the higher insect, as the bee, there is great activity with 

 simple organs of nutrition. In the still higher mam- 

 mal, as man, there is less power of locomotion, though 

 the most perfect nutritive system ; but both functions 

 are subordinate to sensation, which is the crowning 

 development. 



In studying the comparative anatomy and physiology 

 of the animal kingdom, our plan will be to trace the 

 various organs and functions, from their simplest expres- 

 sion upward to the highest complexity. Thus Nutrition 

 will begin with absorption, which is the simplest method 

 of taking food; going higher, we find digestion, but in 

 no particular spot in the body ; next, we see it confined 

 to a tube ; then to a tube with a sac, or stomach ; and, 

 finally, we reach the complex arrangement of the higher 

 animals. 



