44. COMPARATIVE ZOOLOGY. 
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 pow- 
ers of moving and feeling being very feeble. In the 
higher Insect, as the Bee, there is great activity with low 
organs of nutrition. In the still higher Mammal, 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 expression up- 
ward to the highest complexity. Thus, Vuéritcon 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 in Man. 
CHAPTER VI. 
NUTRITION. 
Nutrition is the earliest and most constant of vital 
operations. While the organs of motion and sensation 
seem to be wanting in some lower forms, the means of 
vegetative life are always present. So prominent is the 
nutritive apparatus, that an animal has been likened to a 
moving sac, organized to convert foreign matter into its 
own likeness, to which the complex organs of animal life 
are but auxiliaries. Thus, the bones and muscles are le- 
vers and cords to carry the body about, while the nervous 
system directs its motions in quest of food. 
