236 GLOSSARY 



CENTROLECITHAL. A type of ovum in which the yolk material is mainly 



collected in the center. 



CENTROSOME. The center of radiations in a dividing cell. 

 CEPHALOTHORAX. Fused head and thorax of the majority of the higher 



Crustacea. 

 CHITIN. A lifeless organic substance which forms the basis of protective 



membranes, integuments, shells, and exoskeletons of invertebrates. 

 CHLOROPHYLL. The coloring matter of plants which, under the action of 



sunlight, decomposes carbon dioxide and water and recombines 



the elements in the form of carbohydrates. 

 CHLOROPLASTID. A green, chlorophyll-bearing structure in plant or animal 



cell. 

 CHROMATIN. The deeply staining substance of the nuclear network and 



chromosomes. 

 CHROMOPLASTID. A color-bearing structure other than chloroplastids in 



plant cell. 



CHROMOSOMES. Deeply staining bodies formed by aggregations of chroma- 

 tin during the process of indirect cell division. 

 CLITELLUM. A glandular swelling in the region of the 3Oth to 37th somite 



of the earthworm. It produces the girdle by which two worms are 



held together at copulation. 

 COELOM. The periaxial body cavity of a metazoon with mesodermal wall 



and containing the internal opening of the excretory organ. 

 COLONY. An aggregate or association of individuals. 



COMMENSALISM. Living together in harmony without necessarily con- 

 ferring mutual benefit or harm. 



COMMISSURE. A connecting nerve between ganglia. 



CONJUGATION. The temporary sexual union in protozoa and lower plants. 

 COMPLEMENT. A chemical substance in the blood which acts only through 



association with an intermediate body or amboceptor. 

 CORPORA LUTEA. Firm yellow bodies formed in the Graafian vesicle after 



the discharge of an ovum. 



CRUSTACEA. A group of arthropods with firm exoskeletons. 

 CUTICLE. The lifeless outermost covering of the body of an animal. 

 CYANOPHYLL. A greenish-blue substance derived from chlorophyll. 

 CYCLOSIS. The streaming movements of protoplasm within the cell. 

 CYSTICERCUS. The encysted state of the larva of a tape-worm. 

 CYTOLOGY. The science which deals with cells. 

 CYTOPLASM. The protoplasm of the cell apart from that of the nucleus; the 



cell body. 



DENDRITES. The protoplasmic branching processes of a nerve cell. 

 DIFFERENTIATION. The evolutionary process or result by which originally 



indifferent parts or organs become changed or specialized in either 



form or function; specialization. 

 DIPLOID. Refers, in connection with chromosomes, to the double or normal 



number, half from the male, half from the female parent. 

 DISSEPIMENT. A septum or partition between the somites of annelids. 



