Pulsating vacuoles, see Contracting vacuoles.
Pu' pa, the stage in the development of an insect immediately preceding the adult.
Quill, one of the large, stiff, strong flight feathers or tail feathers of a bird; the hollow, basal part of a feather; a large, hollow, sharp spine.
Ra' di al sym' me try, having the organs or parts arranged symmetrically around a center.
Re gen er a' tion, the power to grow new parts or organs.
Re' gions, the principal divisions of the body, head, thorax, and abdomen.
Res pi ra' tion, the passage of oxygen into the tissues of a living organism and of carbon dioxide out of them. These gases can pass through any thin, moist, organic membrane. When such a membrane separates two fluids which differ in the amount of oxygen they contain, oxygen passes to the fluid containing the smaller amount. The same is true of carbon dioxide. Respiration is believed to occur in all living organisms.
Ro' dent, mammals with curved self-sharpening incisor teeth, order including mice, rats, squirrels, rabbits, etc.
Ros' trum, a beak-like projection or snout.
Ru' mi nant, chewing the cud.