445 ELEMENTS OF BIOLOGY 



Embryology. The science which treats of the processes of development 

 of the organism from the egg to the aduk. 



Emulsification. The process of separation of fats into small droplets 

 suspended in water. 



Enamel. The hard surface layer of teeth and of placoid scales. 



Endocrine glands. Glands that produce hormones and deliver their 

 products by osmosis directly into the blood stream. 



Endocrinology. The science of hormones and of the glands of internal 

 secretion. 



Endoderm. The inner layer of cells formed in the early stage of de- 

 velopment of Metazoa. 



Endolymph. The liquid that fills the membranous parts of the inner 

 ear. 



Endoplasm. That portion of the cytoplasm between the ectosarc and the 

 nucleus of the cell. 



Endosarc. That region of the cell between the ectosarc and the nucleus. 



Endoskeleton. The internal supporting structure of an animal. 



Energy. Power to do work. 



Entomology. The science of insect life. 



Enzyme. Organic substances that by catalytic action cause chemical ac- 

 tions to occur in the organism. 



Epidermis. The outer layer of the vertebrate integument. 



Epigenesis. a concept of embryonic development which holds that the 

 process is one of up-building of adult structures by the constructive 

 nature of embryonic metabolism. 



Erepsin. An enzyme in the vertebrate small intestine that converts in- 

 termediate comp>ounds derived from proteins into amino-acids. 



Erythrocytes. Red blood cells. 



Eugenics. The science of human inheritance. 



Evolution. Organic evolution is a doctrine which holds that present-day 

 organisms are the products of descent with change from earlier 

 and more simple types. 



Excretion. The elimination of wastes of metabolism by the organism. 



Exocrine glands. Glands which deliver their secretion by means of 

 ducts, either to the surface of the body or into some cavity that is 

 indirectly connected with the surface, never into the blood. 



Exoskeleton. The external hard structures of support and protection. 



External fertilization. The meeting of egg and spermatozoon external 

 to the female body. 



