#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. #Sac#, a cavity or pouch. #Sa' crum#, a composite bone formed by the union of vertebræ in the region of hips. #Scap' u la#, the shoulder-blade. #Sep' tum# (pl. #sep' ta#), a wall or partition between two cavities. #Se' ta# (pl. #se' tae#), small bristles or stiff hairs. #Sex' u al#, pertaining to sex. #Si' nus ve no' sus#, an enlargement of the termination of the large veins. #Si' phon#, a tube-like organ. #So' mites#, the serial segments or rings composing the bodies of many animals. #Spe' ci es#, a word used in classification to designate a group of animals differing only in minor details. #Sper' ma ry#, the organ in which sperm cells are developed. #Sperm cells#, the small, often motile, reproductive cell, which fuses with the egg cell. #Spic' ules#, tiny needles of mineral substance found in the walls of many animals, notably sponges. #Spi' ra cle#, an opening into the tracheal breathing organs of insects. #Spire#, the coiled portion of a gasteropod shell. #Spore#, a cell capable of developing into a new organism. #Sternum#, a bone extending along the lower middle line of the chest region. #Stom' ach#, the region of the alimentary canal especially adapted to digest food. #Stom' ach-in tes' tine#, a region of the alimentary canal adapted to both digest and absorb food. #Sub cla' vi an#, situated beneath the clavicle. #Su' ture#, the junction of two contiguous structures. #Swim' mer ets#, the abdominal appendages in crustaceans. #Sym bi o' sis#, an association of two animals which is mutually helpful. #Tar' sal#, one of the bones of the tarsus or ankle. #Tar' sus#, (1) the ankle; (2) the fifth or terminal joint in an insect's leg. #Ten' ta cles#, special organs for touch; also used sometimes for other purposes. #Terrifying attitudes#, protective attitudes assumed by some animals.