726 GLOSSARY. 



Centripetal. Afferent. 



Cerebral vesicles. Primitive swellings on the primary neural tube 



of the early embryo which develop into the brain. 

 Chemical elements. Substances which cannot be split up into com- 

 ponents, and therefore are regarded as simple. 

 Chlorophyll. The green coloring-matter of the cells of plants. It 



is supposed to be the agent which, under the influence of light, . 



decomposes carbon dioxide and water to form the cellulose and 



starch of the plant. 

 Cholesterin. A substance occurring in the bile, white matter of 



the brain and spinal cord, and in small quantities in many 



other tissues. Chemically it is a triatomic alcohol. 

 Chorda dorsalis. The precursor of the vertebral column of the 



embryo. 

 Chorion. The outer layer of the membranes of the ovum, part of 



which becomes vascular, and helps to form the placenta. 

 Choroid. The vascular coat of the eyeball. 

 Chromatic aberration, The alteration of white light into prismatic 



colors during its passage through an ordinary lens. 

 Chyle. The fluid absorbed from the small intestines by the lacteals. 

 Cilia. Minute vibratile processes which occur on the surface cells 



of the respiratory and many other epithelial membranes. 

 Circumvallate. Large papillae situated at the back of the tongue. 



They are surrounded by a fossa in the walls of which lie taste 



buds. 

 Cloaca. The common opening of the genito-urinary organs into 



the primitive hind-gut of the embryo. The cloaca persists in 



birds. 

 Colloid. That condition of quasi-dissolved matter in which it will 



not diffuse through a membrane such as parchment. The op- 

 posite of crystalloid. 

 Co-ordination. The adjustment of separate actions for a definite 



result, as when the nerve-centres cause various distinct muscles 



to act together and produce complex movements. 

 Cytod. A term suggested to denote a living protoplasmic unit 



which has no nucleus. 



Decidua reflexa. The outgrowth of the uterine mucous membrane 



which surrounds the ovum. 

 Decidua serotina. The part of the modified mucous membrane of 



the uterus in which the fecundated ovum is lodged. 



