GENERAL ZOOLOGY 



ENDOCRINOLOGY. The science of the endocrines. 



ENDODERM. The innermost of the two germ layers formed during gastrulation; 

 forms the wall of the archenteron; sometimes called entoderm. Cf. ECTODERM 

 and MESODERM. 



ENDOMIXIS. A reproductive or pre-reproductive process characteristic of some 

 ciliates, such as Paramecium; apparently somewhat analogous to the process of 

 CONJUGATION but differs in that the changes involve only a single individual. 



ENDOPARASITE. A parasite that lives within its host. Cf. ECTOPARASITE. 



ENDOPLASM. The interior cytoplasm of a protozoan or of any other cell. 



ENDOSKELETON. An internal skeleton; a cellular supporting structure formed from 

 mesoderm. Cf. EXOSKELETON and SKELETON. 



ENDOTHERMOUS. Animals possessing the capacity of maintaining a constant, or 

 nearly constant, body temperature in the face of marked changes in the tempera- 

 ture of their environment; loosely, "warm-blooded." 



ENERGY. See TRANSFORMATION OF ENERGY. 



ENTEROCOEL. A true coelom formed primitively by the expansion into the blastocoel 

 of hollow evaginations from the wall of the archenteron, or by a process evi- 

 dently derived from such a type of development. Cf. SCHIZOCOEL. 



ENTERON. A digestive cavity or tube lined by a cellular layer, the gastrodermis, of 

 endodermal origin. 



ENTODERM. Variant spelling of ENDODERM. 



ENTOMOLOGIST. A student of the insects. 



ENVIRONMENT. The total of surrounding conditions, usually with reference to the 

 organism as a whole; in this sense, the external environment, as contrasted with 

 the internal environment, or immediate surroundings of a part of an organism. 



ENZYME. An organic catalyst, or substance that affects the rate of a chemical re- 

 action but does not appear as one of its end products; there are many kinds of 

 rn/\ mes, and they are produced by all cells. 



EPIDERMIS. The outer cellular layer of the body; the outer layer of the skin, an 

 epithelium of ectodermal origin. 



EQUILIBRIUM. The state of being balanced. 



ERYTHROCYTE. A red blood cell. Cf. LEUCOCYTE and LYMPHOCYTE. 



EUCOELOMATE. A metazoan possessing a true coelom. See COELOM. 



EUGENICS. The science that applies the principles of genetics for the purpose of 

 human betterment. 



EUGLENOID. Pertaining to or resembling the euglena. 



EVAGINATION. The movement of a group or layer of cells away from a cavity. Cf. 

 INVAGINATION. 



EVIDENCE. Facts related to some particular event. 



EVOLUTION. The process of natural, consecutive change. Cf. ORGANIC EVOLUTION. 



EXCRETA (sometimes EXCRETIONS). Waste products of metabolism, to be eliminated 

 from the body. 



EXCRETION. The process of elimination of the metabolic wastes. 



EXCRETORY. Pertaining to the elimination of metabolic waste products. 



EXCRETORY TUBULE. Any small duct that conveys nitrogenous waste products, such 

 as the kidney tubules of vertebrates, the Malpighian tubules of insects, and the 

 nephridia. 



EXCURRENT. Affording an exit; leading outward. Cf. INCURRENT. 



EXCYSTMENT. Emergence from a cyst. Cf. ENCYSTMENT. 



EXOSKELETON. An external skeleton; a non-cellular, non-living structure, lying at 

 the surface of the body, produced by the epidermis. Cf. ENDOSKELETON and 

 SKELETON. 



EXPERIMENTAL BREEDING. Breeding in such a way that the method of inheritance of 

 given characters can be determined. See HYBRIDIZATION. 



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