466 GENERAL ZOOLOGY 



Coelom. The body cavity of the vertebrate type, lined with mesothelium 



and containing the viscera attached by mesenteries. It is entirely 



distinct from the digestive cavity of the alimentary canal. 

 Collagen. A gelatinlike protein. 

 Colloid. A state of matter consisting of a dispersed system of molecular 



aggregates. 

 Colony. A group of individuals of the same species, often organically 



connected, forming a unit of a higher order than the individual. 

 Commensalism. The association of two or more individuals of different 



species, often for mutual benefit. 

 Concave. Curved inward. 

 Conjugation. A temporary union of two Protozoa during which an 



exchange of nuclear material takes place. 

 Convex. Curved outward. Bulging out. 

 Copulation. The sexual act during which spermatozoa are transferred 



from the male to the female; or the sexual act of two monoecious 



animals. 

 Cortex. The outer region of a cell or organ. 

 Cranial. Pertaining to the cranium, the portion of the skull enclosing the 



brain. 

 Cretinism. A condition characterized by subnormal mental and physical 



development, caused by thyroid insufficiency. 

 Cuticle. The outer layer covering the surface of the organic body. It 



may be a secretion product of underlying cells, as in many invertebrates, 



or it may be composed of dead cells, as in the stratum corneum of human 



skin. 

 Cytoplasm. The extranuclear part of a cell; the cytosome. 

 Cytozoic. Parasitic in a cell. 



Darwinism. The explanation of evolution by the theory of Natural Selec- 

 tion as set forth by Charles Darwin. 

 Deaminization. The process in the body by which nitrogenous radicals 



are removed from amino acids, thus liberating nonnitrogenous portions 



capable of oxidation and energy production. 

 Differentiation. In embryogeny the transformation of blastomeres 



into tissues and organs. In general, a change from homogeneity to 



heterogeneity. 

 Digestion. The result of the action of digestive agents on food which 



reduces food to a liquid condition capable of absorption and assimila- 

 tion by living cells. 

 Dioecious. A condition in which the male and female organs, testis and 



ovary, are borne by different individuals. 

 Diploblastic. Having two germ layers. 

 Diploid. The unreduced number of chromosomes. 

 Distal. Remote from point of origin or attachment. 

 Diuresis. Free or excessive secretion of urine. 

 Dorsal. Pertaining to the back. 

 Ductless gland. A gland whose secretion is poured directly into the blood 



stream. An endocrine gland. 



