_Cephalopoda._ The highest class of mollusks. _Cereal._ A grass which produces edible grain. _Cerium._ A metallic element. Symbol: Ce. _Cetacea._ The order of mammals including the whales. _Chemistry._ The science which deals with the composition of matter and its transformations. _Chiroptera._ An order containing the bats. _Chloride._ A chlorine compound. _Chlorine._ A gaseous element. Symbol: Cl. _Chlorophyll._ The coloring-matter of green parts of plants. _Chromatic aberration._ The colored fringe seen at the edges of images formed by a simple lens, because of the difference in wave lengths of the various rays. _Chromium._ A metallic element. Symbol: Cr. _Chromo-._ Color-, in many compounds. Also: chroma-, chromato-. _Chromosome._ One of the small bodies formed out of a protoplasmic substance (chromatin) in the nucleus before a cell divides. _Civilization._ An advanced stage of culture. Civilization is sometimes contrasted with culture, but the matter is one which cannot be considered here. _Class._ A group of animals or plants, more comprehensive than an order and less so than a phylum. _Climate._ The average weather conditions of a particular place or region. _Cobalt._ A metallic element. Symbol: Co. _Coccus._ A spherical bacterium. A sort of carpel. _Coelenterata._ A phylum of invertebrate animals including the corals. _Cohesion._ Molecular attraction within a body. _Colloid._ Not crystalloid. A substance which does not form a true solution. Colloidal liquids have very little osmotic pressure. _Columbium_ or _niobium_. A metallic element. Symbol: Cb. _Combustion._ Oxidation accompanied by the production of heat and light. Less frequently, the word is used for a combination which is not oxidation or where no heat or light is produced. _Common sense._ Ordinary and non-scientific thought processes. Scientific thinking is more exact and more fertile. _Community._ A social group. _Comparative._ Involving comparison, as between man and the other animals. _Complex._ In psycho-analysis, a cluster of ideas and mental images joined together by a stressed emotion; especially such a cluster that is thrust out of consciousness (repressed). _Component of a force._ The effective value of a force in a given direction. _Compound._ A substance consisting of two or more chemical elements in combination. _Compound animal, flower, leaf, etc._ An animal, etc., consisting of a combination of organisms or simple parts. _Conation._ Will, directing power, effort. _Concave._ Curved like the interior of a circle or sphere. _Concept_ or _conception_. The idea, notion, or thought held about anything. Conception includes symbol and meaning. _Condense._ Change from gas to liquid. Concentrate (electricity). Of organic compounds, react in a certain way so as to form new bonds. _Conduct._ Carry heat or electricity. _Conductance._ Ability to conduct. The word is used to describe the property of a conductor.