498 APPENDIX 



Endoplasm. The inner cytoplasm surrounding the nucleus; e.g., in 

 Amoeba, Paramecium. See Ectoplasm. 



Endopodite. The inner of the two distal parts of the typical biramous 

 Crustacean appendage. See Protopodite and Exopodite. 



Endoskeleton. An internal living skeleton affording support and protec- 

 tion, as well as levers for the attachment of muscles. Characteristic of 

 Vertebrates. 



Energy. See Potential Energy. 



Enteric Cavity. The digestive cavity of the gastrula stage, and of simple 

 Metazoa, e.g., Hydra. 



Enteron. Enteric pouch forming the wall of the enteric cavity. 



Enterozoa. Animals with an enteron, and with or without a coelom. 

 All animals above the Sponges. See Parazoa. 



Enzymes. Special chemical substances (apparently proteins) of organ- 

 isms, which bring about by catalytic action many of the chemical 

 processes of the body; e.g., digestion. See Catalysis. 



Epidermis. The outer cellular layer of the skin. 



Epigenesis. Development from absolute or relative simplicity to com- 

 plexity. See Preformation. 



Epithelium. A layer of cells covering an external or internal surface, 

 including the essential secreting cells of glands. 



Equatorial Plate. The equator of the spindle with its group of chromo- 

 somes during the metaphase of mitosis. 



Esophagus. Tubular passage from pharynx to stomach. 



Eugenics. The system of improving the human race by breeding the best. 

 "The science of being well born." See Euthenics. 



Eustachian Ture. Passage connecting the Vertebrate middle ear with 

 the pharynx. Remnant of the most anterior gill slit, represented in 

 present-day Sharks by the 'blow-hole,' or spiracle. 



Euthenics. The system of improving the human race by good environ- 

 ment. See Eugenics. 



Eutheria. The highest of the three subclasses of Mammals, including all 

 the familiar forms. Placentals. See Appendix I. 



Evolution, Organic. Present-day organisms are the result of descent 

 with change from those of the past. 



Excretion. The elimination of waste products of metabolism. A waste 

 product. See Secretion. 



Exopodite. The outer of the two distal parts of the typical biramous 

 Crustacean appendage. See Protopodite and Endopodite. 



Exoskeleton. A non-living external skeleton chiefly for protection. The 

 characteristic skeleton of Invertebrates; e.g., Crayfish. 



External Receptors. Sense organs upon the surface of the body. See 

 Internal Receptors. 



