_Brachiopods_: Invertebrate animals bearing a superficial resemblance to bivalve molluscs, but belonging to a totally different group—lamp shells. _Cambrian_: The “oldest” system of the Palæozoic group of fossiliferous rocks. _Carbohydrates_: The sugars, starches, etc.,—polyhydric alcohols with aldehydic or ketonic groups, and acetals of same, etc. _Catalyst_: A substance which accelerates a chemical reaction without permanently participating in it, being left over unchanged at the end of the process. _Centriole_: The centrioles or central bodies are the foci of mitotic division in animal cells, as well as the source of the kinetic elements developed by such cells. They are minute bodies usually located within a larger sphere known as the centrosome or centrosphere. They do not occur in the cells of the higher plants. _Cephalopods_: A class of molluscs in which the foot is developed into a headlike structure with eyes and a circle of arms, _e.g._, the octopus, the cuttlefish, the squid, and the nautilus. _Ceratites_: A genus of extinct cephalopods having a coiled shell and crooked sutures. _Character_: An external feature or sensible property of an organism. It is the joint product of germinal factors (genes) and environmental influences. _Chlorophyll_: The green pigment formed in the chloroplasts (green plastids) of plant cells. It is a diester of phytyl and methyl alcohols with the tribasic acid, chlorophyllin, one of whose carboxyls is esterified with methyl alcohol, a second with phytol, while the third is otherwise engaged. Chlorophyllin is a tribasic acid consisting of the chlorophyllic chromogen group (containing magnesium) joined to three carboxyl groups. _Chondriosomes_: Cytoplasmic granules rodlike, threadlike, or spherical in form, which often appear to divide on the mitotic spindle, and are therefore credited with the power of independent growth and division. The chondriosomes of embryonic tissues are thought to be the original sources of the plastids, the fibrillæ, and certain metaplastic granules. _Chordates_: The phylum of animals whose primary axial skeleton consists temporarily or permanently of a notochord. _Chromatin_: Same as basichromatin. _Chromosomes_: The short threads or rodlike bodies into which the basichromatin of the cell-nucleus is aggregated during mitosis—each chromosome is segmented into granules called chromomeres—in its submicroscopic structure it consists of chain or linear series of genes (hereditary factors) representing characters linked together in heredity, each single chromosome being termed, on this account, a “linkage-group” by geneticists.