240 GLOSSARY 



BLASTULA. An early stage in development of the egg prior to the gastrula 



or two-layer stage. 

 BKANCHIOSTEGITE. Lateral gill-protecting portion of the crustacean exo- 



skeleton. 



BUCCAL CAVITY. Mouth cavity. 

 CARBOHYDRATE. Any organic body containing carbon, with hydrogen 



and oxygen in the proportions represented by water (H 2 O). 

 CELL. A unit mass of protoplasm consisting of nucleus (or nuclei) and 



cell body or cytoplasm. 

 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. Fased 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. 



CHROMOGEN. The nitrogen-holding portion of the chlorophyll molecule. 

 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. 

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



association with an intermediate body or amboceptor. 



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

 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. 



