#Com pressed' #, narrower from side to side than from dorsal to ventral surface.

#Con ju ga' tion#, a process occurring in some one-celled animals, preceding reproduction. In this process two animals unite temporarily and exchange nuclear substance, or in some forms the two cells fuse into one. After this exchange or fusion fission occurs, usually more rapidly than before.

#Contracting# or #pulsating vacuoles#, small, clear spots in a cell, filled with a watery fluid. In the living animal these alternately disappear and then reappear.

#Co' nus ar te ri o' sus#, a cone-shaped artery connected with the ventricle of the heart.

#Cov' ert#, a feather overlying the base of the large feathers of the wing or tail.

#Cra' ni um#, the skull, particularly that part of it inclosing the brain.

#Crop#, an enlarged portion of the esophagus.

#Cross fertilization#, a form of fertilization in which the male and female elements are produced by different individuals.

#Crus ta' ce a#, aquatic, gill-bearing arthropods, with two pairs of antennae.

#Cu' ti cle#, the thin outer skin.

#Cy' to plasm#, the portion of the protoplasm of a cell which is outside of the nucleus, less dense than the nucleus and usually taking a lighter stain.

#Den' ta ry#, the terminal portion or bone of the lower jaw of vertebrates lower than mammals, containing all or most of the teeth.

#Di a phragm#, a muscular part.i.tion separating the abdomen and thorax, in mammals.

#Dig' i ti grade#, walking on the toes.

#Di ' cious#, reproductive organs in different individuals.

#Dip' te ra#, insects with two wings, including flies, mosquitoes, etc.

#Dis' tal end#, the free end of any object which is attached by one end.

#Dor' sal surface#, the upper surface; the back.

#Du' o de' num#, the first portion of the small intestine.

#Ec' to derm cells#, cells covering the outside of sponges and some other simple animals.

#Egg cell#, the large, non-motile reproductive cell, with which a sperm cell fuses.

#Em bry on' ic#, development within the egg or in the body of the mother.

#En' do derm cells#, cells lining inner cavities in the many-celled animals. As a rule they have cilia or flagella.

#E soph' a gus#, the portion of the alimentary ca.n.a.l connecting the mouth (or the pharynx) with the stomach.

#Eu sta' chi an# (eu sta' kian) #tube#, a pa.s.sage between the pharynx and the middle ear.

#Ex ha' lent#, flowing or moving away from the body.

#Ex' o skel' e ton#, an external skeleton.

#Eye stalk#, an appendage which bears an eye on its free end.

#Fe' mur#, (1) the thigh bone; (2) the third joint of an insect's leg.

#Fer ti li za' tion#, the fusion of male and female elements in reproduction.

#Fi' bers#, flexible threads; fibers of a h.o.r.n.y material are found in the walls of many of the sponges.

#Fib' u la#, the outer of the two long bones of the lower leg.

#Fin#, a paddle-like structure for swimming.

#Fin-rays#, the framework of the fins of fishes.

#Fis' sion#, a method of reproduction used in all cells, by which a cell divides itself into two, usually through the center. _See also_ Conjugation and Budding.

#Fla gel' lum# (pl. #flagella#), vibrating hairs larger than cilia and less numerous.

#Food-b.a.l.l.s#, bits of food inside the cells of many one-celled animals, usually showing through the walls.

#Food-vacuole#, a small drop of water containing digestive material and a food-ball.

#Fo ra' men#, an opening or short pa.s.sage.

#Gall-bladder#, a membranous sac for the storage of gall, or bile, at the lower edge of the liver (syn. "bile sac").

#Gas ter op' o da#, the cla.s.s to which the snail belongs.

#Ge' nus# (pl. #genera#), a group of closely related species.

#Germ-spot#, the region in the bird's egg in which development first takes place.

#Gill#, an apparatus for breathing the air dissolved in water.

#Gill-cham' ber#, a pocket or cavity covered by a flap, in which the gills lie.

#Gir' dle#, the name applied to the smooth band often occurring near the anterior end of an earthworm.

#Giz' zard#, a portion of the alimentary ca.n.a.l with especially thickened muscular walls.

#Glot' tis#, the opening between the vocal cords, or the mouth of the windpipe.