GLOSSARY 465 



Catalysis. The acceleration in rate of a chemical reaction by an agent 



which itself remains unchanged. 

 Caudad. Toward the tail. 

 Caudal. Pertaining to the tail. 



Cell. A small mass of protoplasm containing one or more nuclei. 

 Cell doctrine. That all organisms are composed of cells and the products 



of cells; that the cell is a functional and structural unit of the organic 



body. 

 Cellulose. A carbohydrate found in the walls of plant cells. Its occur- 

 rence in animal tissues is rare. 

 Centigrade thermometer. One in which 0° is the freezing point and 100° 



the boiling point of water. 

 Centimeter. A unit of linear measurement in the metric system. Abbre- 

 viation: cm.; (2.54 centimeters = 1 inch). 

 Cephalad. Toward the head or anterior end. 

 Cephalic. Pertaining to the head. 

 Cercus. Either of a pair of appendages at the posterior end of the body of 



arthropods. 

 Cervical. Pertaining to the neck. 



Characters or characteristics. Physical, mental, and physiological traits. 

 Chlorophyll. An important plant pigment, concerned in photosynthesis. 

 Chondrocranium. A continuous cartilaginous structure incompletely 



enclosing the brain. It occurs in the embryos of all vertebrates and 



in the adult sharks and lampreys. 

 Chordate. An animal in which the notochord is or represents the skeletal 



axis during some period of its life history. All vertebrates are chordates. 

 Chromatic. Pertaining to color. 

 Chromatin. The deeply staining substance of the nucleus which forms 



into chromosomes when the cell divides. 

 Chromatophore. A cellular organ containing pigment. 

 Chyle. The fatty contents of the lacteals of the intestines. 

 Chyme. Partly digested food as it occurs in the stomach and intestine. 

 Cilia. Hair-like processes of Protozoa and ciliated epithelial cells. 

 Circulation. The movement of the blood or body fluid through a more or 



less complete system of vessels. 

 Cirrus. A soft tentaclelike appendage. 

 Class. One of the principal subdivisions of a phylum in the system of 



classification. 

 Cleavage. The period of cell division following fertilization, during which 



the egg is converted into a blastula. Parthenogenetic eggs also 



undergo cleavage. 

 Cloaca. A common cavity into which open the urogenital ducts and the 



alimentary canal, in fishes, amphibia, reptiles, birds, and the lowest 



group of mammals (Prototheria). 

 Cocoon. A case in which eggs are deposited and in which larvae may 



develop; a protective covering of mucus secreted by the integument. 

 Coelenteron. A saclike body cavity in which digestion and absorption 



of food take place. Same as gastrovascular cavity, 



