GLOSSARY OF EMBRYOLOGICAL TERMS 277 



Equational Maturation Division — maturational divisions in which there is 

 no (qualitative) reduction in chromosomal complex, similar in results 

 to mitosis. 



Equatorial Plate — lateral view of chromosomes, lined up on mitotic spin- 

 dle, prior to any anaphase movement. 



Eustachian Tube — vestige of endodermal portion of hyomandibular pouch 

 connecting middle ear and pharyngeal cavities and lined with endo- 

 derm. 



Evagination — growth from any surface outward. 



"Ex Ovo Omnia" — -all life comes from the egg (Harvey, 1657). 



Exogastrula — gastrulation modified experimentally by abnormal condi- 

 tions so that invagination is partially or totally hindered and there 

 remains some mesendoderm not enclosed by ectoderm. 



Experimental Method — concerted, organized, and scientific analysis of the 

 causes, forces, and factors operating in any (embryological) system. 



External Gills — outgrowths of (amphibian) branchial arches which func- 

 tion as temporary (anura) or permanent neotonic (urodela) respira- 

 tory organs. 



Extra-Embryonic — refers to structures apart from embryonic body, such 

 as membranes. 



Fate Map — map of blastula or early gastrula stage which indicates pro- 

 spective significance of various surface areas, based upon previously 

 established studies of normal development aided by means of vital 

 dye markings. 



Fate, Prospective — destination toward which we know, from previous ex- 

 perience, that a given part would develop under normal conditions; 

 lineage of each part of egg through its cell descendants into a definite 

 region or portion of adult organism. 



Fertilization — activation of egg by sperm and syngamy of pronuclei; union 

 of male and female gamete nuclei. 



Fertilization, Anti "eggs contain within their interior a substance capa- 

 ble of combining with the agglutinating group of the fertilizin, but 

 which is separate from it as long as the egg is inactive" (Lillie). 



Feulgen Reaction — chemical test for thymo-nucleic acid, used as a specific 

 staining test for chromatin. 



Field — mosaic of spatio-temporal activities within developing organism. 



