GLOSSARY 377 



Elodea {eV o de' a). A genus of aquatic plants. 



Embryo {em' bri o). An undeveloped animal while still in the egg membrane or in the 



maternal uterus. 

 Embryology (em' bri oV o ji). The science which deals with the development of the 



embryo, or young stages, of animals or plants. 

 Embryonic (em' hri on' ic). Pertaining to an embryo. 

 Empedocles (em ped' o kleez). Greek philosopher and poet, born in Sicily. Lived 



about 490-430 B.C. 

 Empirical formula (em peer' i kalfor' mu la). A formula stating merely the number 



of atoms of the various elements in a molecule of a chemical substance. 

 Emulsion (e muV shun). A mixture of two liquids or semi-liquid substances, neither 



one soluble in the other, the one being in the form of separate droplets suspended in 



the other. 

 Enamel (en am' el). The very hard, polished calcareous substance forming the 



surface layer or internal plates in the teeth of mammals. 

 Endoderm (en' do derm). The inner layer of cells of a gastrula, or the representative 



of this layer in later stages. 

 Endosarc (en' do sark). The inner mass of protoplasm in cells in which the outer and 



inner protoplasm differ in structure. 

 Enterokinase (en' ter o ki' nase). An enzyme produced in the small intestine and 



serving to convert trypsinogen into trypsin. 

 Enteropneusta (en' te rop nu' sta). A subphylum of Chordata, worm-like animals, 



of which Balanoglossus and Cephalodiscus are representatives. 

 Entomology (en' to moV o ji). The zoology of insects. 



Entoparasite (en' to par' a site). A parasite that lives within the body of its host. 

 Enzyme (en' zime). An organic substance which brings about a chemical reaction 



but is not consumed by that reaction. Probably it participates in the reaction, but 



is promptly restored. 

 Eocene (e' o seen). Of the earliest Cenozoic and Tertiary time. 

 Eohippus (e' o hip' pus). The earliest known ancestor of the horse, an extinct animal 



of Eocene time. 

 Epidermis (ep' i der' mis). The outer of the two principal layers of the skin. Also 



an outer layer of cells in general. 

 Epistylis (ep' i sti' lis). A genus of colonial ciliated Protozoa, resembUng Vorticella. 



E. fiavicans (flav' i kanz), one of the species. 

 Epithelial (ep' i the' li al). Pertaining to an epithelium; as, epithehal tissues or 



structures. 

 Epithelium (ep' i the' li urn). A layer of cells at the surface of a tissue or organ, or 



hning a cavity. 

 Equatorial (e' kioa to' ri al). In the plane of a great circle half way between the poles; 



said of a cleavage plane of an egg. Also, in a middle position in other objects. 

 Equatorial plate (e' kwa to' ri al plate'). The flattened group of chromosomes on the 



middle of the spindle of a dividing cell. 

 Equus (e'kwus). A genus of animals including the living horse and some of its fossil 



relatives of Pliocene and Pleistocene time. 

 Erepsin (e rep' sin). A proteolytic enzyme produced in the small intestine. 

 Erosion (e ro' zhun). The wearing away (of rocks) through the action of water and 

 other agencies. 



