GLOSSARY k63 



EBEEBA'S LAW - "a cellular membrane at the moment of its formation tends to assume the form which would be 

 assumed under the same conditions by an elastic membrane destitute of weight" (Gray, 1931). 



ESTEOGEN - secretion product of the ovary which controls oestrus and endometrial growth. 



ESTBOUS CYCLE - the periodic series of changes which occur in the mammalian uterus, related to the prepara- 

 tion of the uterus for implantation of the ovum, and to repair. 



ESTBUS - period of the reproductive cycle of the mammal when the uterus is prepared for implantation of the 

 ovum. 



ETHEOGENESIS - development of the spermatozoSn without fertilization; male parthenogeneaia. 



EUCHEOMATIN - the part of the regular chromatic structure of the nucleus which Is rich in thymonucleic 



acid, and presumably the genes, alternating (in the chromosomes) with achromatic regions. It is in 

 the form of discs, and takes methyl green stain. 



EUPLOIDY - deviation from the normal diploid condition but Involving complete sets of chromosomes 

 (Tackholm, 1922). 



EUTELY - constancy of cell numbers in the various organs of plants and animals, more dependable in animals 

 than in plants (Wettstein, 1927, Heilbom, 1954). 



EVAGINATION - the growth from any surface outward. 



EVOCATION - mere calling forth of potentialities through contact; non-assimilative induction, no organiza- 

 tion except that which is present within the host material; that portion of the inductive response 

 which can be achieved by killed, crushed, or narcotized organizers of any level. 



EVOCATOE - a chemical substance which has the power of calling forth the latent potentialities of an 

 embiyonic area; a morphogenetic stimulus. 



EXCLUSIVITY - discreteness of the differentiation process (Weiss). 



EXGENITO-VIVIPAEITY - the embryo in a stage of development which corresponds to the egg stage of ovo- 



viviparous forms, obtains its nourishment by means of a trophamnion, trophoserosa or trophochorlon. 

 Development occurs in the haemocoele, not in the uterus (e.g., Strepsyatera). 



EXOGASTEULA - gaatrulation modified experimentally by abnormal conditions so that invagination is partial- 

 ly hindered and there remains some mesendoderm not enclosed by ectoderm; evaglnatlon of the primary 

 intestinal cavity, or archenteron. (See vegetativisatlon. ) 



EXOGENOUS - originating from without the organism. 



"EX OVO OMNIA" - all life comes from the egg (Harvey, l65T). 



EXPEEIMENTAL ^4ETH0D - concerted, organized, and scientific analysis of the causes, forces, and factors 

 operating in any (embryologlcal) system. 



EXPEEIKENTUM CEUCIS - the final, concluding experiment when a control is no longer needed; presumably a 

 method of final and- triumphal demonstration when all pioneer work has come to a successful ending. 



EXPLANATION - culturing of isolated blastema or tissues in vitro. 



EXPBESSIVITY - the degree to which a group of organisms is affected by the presence of a particular gene 

 (see penetrance). 



EXTENSION - process of gastrulatlon; elongation of central cells of the marginal zone, and then the more 

 peripheral cells, toward the groove of the blastopore. Syn., elongation, aelf-stretohlng 

 (Schechtman), Strekung, Staffelung (Vogt). 



EXTEA-OVATE - extrusion of a portion of the egg substance beyond the cell boundary, achieved in hypotonic 

 solutions. Syn., exovate. 



EYE, ANTEEIOE CHAKBEE OF - one of the best sites for observation of transplanted tissues, which tissues 

 can be seen through the transparent cornea. The aqueous humor often is not as species specific as 

 a nutrient environment as may be other tissues of the same organism. 



FAEBLOSE PIGMENTZET.T.KH - colorless pigment cell in dermal and subcutaneous tissues (e.g., in axolotl). 

 (Schuberg, 1903 •) 



FATE MAP - a map of a blastula or early gastrula stage which indicates the prospective significance of 

 the various surface areas, based upon previously established studies of normal development aided 

 by means of vital dye markings. 



FATE, PEOSPECTTVE - destination towards which we know, from previous experience, that a given part would 

 develop under normal conditions; lineage of each part of the egg through its cell descendants into 

 a definite region or portion of the adult organism. 



FEEDING, MAXIMAL - procedure whereby the organism is provided with all the food that it can possibly con- 

 sume. 



FETUS PAFYEACEUS - compressed fetus, abnormal: "paper-doll fetus". 



FEETILIZATION - activation of the egg by a spermatozoon and syngany of the two pronuclei; union of male 

 and female gamete nuclei; amphimixis. 



FEETILIZATION CONE - conical projection of the egg cortex to meet the spermatozoon destined to invade 

 the egg, generally engulfing the spermatozoon. Seen in annelids, molluscus, echinoderms, and 

 ascidians. 



FEETILIZATION, DRY - placing milt (concentrated sperm) of aquatic forme directly over practically iry 

 eggs, the procedure allowing greater concentration of sperm before flooding the eggs with water. 



FEETILIZATION, FEACTIONAL - fertilization following partial removal of sperm by centrifugation after 



partial penetration (Llllie, 1912). Elongated heads of some sperm (e.g.. Nereis) are easily frag- 

 mented during penetration by centrifugation. 



FEETILIZATION MEMBRANE - a non-living membrane seen to be distinct from the egg shortly after fertiliza- 

 tion, very probably the vitelline membrane elevated off of the egg (or from which the egg has 

 shriinken away by exosmosis). (See Gostello, 1939:Phy3. Zool. 12.) 



