GLOSSARY 



CHROMATID. A half-chromosome; one of the four half-chromosomes forming a 

 tetrad. 



CHROMATIN. The readily stainable substance of the nucleus, most conspicuous during 

 mitosis. 



CHROMATOPHORES. Pigment-bearing cells, frequently capable of changes in shape 

 and responsible for the color changes in animals like the chameleon and the 

 squid. 



CHROMOSOMAL ABERRATION. Any loss or gain of a part of a particular chromosome, 

 of a whole chromosome, or of a haploid set of chromosomes; may give rise to 

 a heritable variation. 



CHROMOSOME. A mass of chromatin, of characteristic size and shape, visible in 

 the nucleus at the time of mitosis; composed of a matrix containing at least two 

 genonemata. 



CILIA {.sino. CILIUM). Short, hair-like protoplasmic extensions from the free surfaces 

 of certain cells; capable of vibration and usuallv numerous. Cf. FLAGELLUM. 



CIRCULATING FLUIDS. Blood and lymph. 



CIRRUS (/?/. CIRRI). A slender extension, occurring singly or in groups and fre- 

 quently curved; a name used for many structures of diverse functions. 



CLASS. A subdivision of a phylum; a group of next higher rank than an order. 



CLASSIFICATION. The grouping together of organisms that tiave certain structural 

 features in common. 



CLEAVAGE. Cell division during the early period of development. 



CLEAVAGE CAVITY. See BLASTULA CAVITY. 



CLOACA. A common chamber through which egested and certain excreted ma- 

 terials, as well as the germ cells, leave the bodies of many vertebrates; 

 analogous regions in some invertebrates. 



CM. Abbreviation for centimeter. 



COELOM {pi. COELOMATA). The body cavity of eucoelomate Metazoa, formed in 

 and surrounded by mesodermal tissues; having a continuous peritoneal lining 

 and a characteristic relationship to reproductive organs and nephridia. May 

 be continuous or divided into chambers by partitions. Cf. BODY CAVITY, 

 HEMOCOEL, PSEUDOCOEL. 



COLONY. A group of individuals, unicellular or multicellular and of the same species, 

 that have arisen from a common parent cell and remain attached or held to- 

 gether; also, insect societies. 



COMMENSALISM. A form of symbiosis consisting of an association of two or more 

 individuals, of different species, of which neither is parasitic but in which some 

 benefit of the association may accrue to one rather than to both of the members. 

 Cf. MUTUALISM and PARASITISM. 



COMMISSURE. A connection between two ganglia of a pair, or right and left parts 

 of the nervous system. Cf. CONNECTIVE. 



COMMON CARRIER. A circulating fluid which transports numerous substances to and 

 from the various parts of the body. 



COMMON CENTER OF ORIGIN. A place in which the ancestors of different but re- 

 lated kinds of animals lived and from which they migrated over all possible 

 routes as evolution occurred. 



COMMUNITY. Collective term for all the organisms living in a particular general 

 environment, interacting with each other and with the conditions characteristic 

 of the environment. 



COMPETITION. Relationship existing between two or more diflferent organisms, or 

 diff^erent kinds of organisms, both or all of which depend for their lives on 

 certain foods, or substances, or space, available in their environment in only 

 limited amounts. One of the bases for the "struggle for existence" between 

 organisms in an environment. 



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