370 PRINCIPLES OF ANIMAL BIOLOGY 



Clavicle. The collar bone in man. One of the bones of the ventral part of tlie 



pectoral girdle in vertebrates in general. 

 Cleavage. The division or segmentation of an egg. 



Clitellum. A thickened glandular band encircling the body of an earthworm. 

 Cloaca {klo a' ka). A common passageway through which the intestine, kidneys, 



and sexual organs discharge their products in some fishes, in amphibia, reptiles, 



and birds, and in a few mammals. 

 Cnidoblast (?//' do blast). A cell containing a nematocyst or stinging thread in Hydra 



or other Coelenterata. 

 Coagulation. Hardening; specifically, the clotting of the blood. 

 Cocoon. A case in which eggs are stored and in which frequently the larvae are 



developed; also a silky covering around the pupa. 

 Codosiga iko' do si' go). A genus of flagellate Protozoa having a collar around the 



flagellum. 

 Coelenterata {se Icn' ter a' ta). The phylum to which Hydra, the hydroids, jelly- 

 fishes, and siphonophores belong. For definition see Chap. 19. 

 Coelenteron (se len' ter on). A cavity in forms like Hydra which have only one body 



cavity. It serves the digestive and circulatory functions and is therefore also 



called the gastrovascular cavity. It has only one opening. 

 Coelom (see' lome). The true body cavity, a cavity within the mesoderm on the w^alls 



of which the principal reproductive organs are located. 

 Coenosarc {se' no sark). The celhilar living part of a hydroid, as distinguished from 



the j)erisarc. 

 Collared epithelium. Epithelivim each of whose cells bears a collar. 

 Collecting tubule. One of a number of tubes leading across the kidney of the frog 



from Bidder's canal to the ureter. 

 Colloid (koV lord). A mixture in which particles invisible through a microscope but 



greater in size than molecules are held in suspension in a liquid. 

 Colloidal (kol loi' dal). Contained in a liquid in aggregations submicroscopic in size 



but greater than molecules. 

 Colony. A group of individuals of the same species organicall}- connected with each 



other. 

 Coluber. A genus of snakes. 

 Columnar epithelium. Epithelium in which the cells have one dimension distinctly 



greater than the others, that dimension being vertical to the surface covered by 



the epithelium. 

 Comanchean {ko man' che an). Pertaining to Mesozoic time prior to the Cretaceous; 



formerly called lower Cretaceous. 

 Common bile duct. The tube leading from the liver to the small intestine and serv- 

 ing to convey bile to the small intestine. 

 Compound. A substance produced by two or more elements in combination. 

 Compound gland. A branching gland. 

 Conemaugh iko' ne maw). A rock formation of eastern United States, belonging to 



Permocarboniferous time. 

 Coniferous. Cone-bearing (as pine or cypress trees). 

 Conjugation. The meeting of two cells for exchaiige of nuclear material or (by exten- 



.-^ioii of meaning) for complete fusion. 

 Connective tissue. .\ tissue composed of cells and ('(MtMiii other material protluccd 



by the cells, which in its simple foiin binds organs and other tissues togeth(M'. in 



a broader sense it includes such modified tissues as cartilage, bone, tendon, and 



liganiejits. 

 Contractile tissue. .\ny tissue cajjable of acti\(' contraction: as muscle. 



