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GLOSSARY 



EXOGENOUS - originating from without the or- 

 ganism. 



"EX OVO OMNIA" - all life comes from the 

 egg (Harvey, 1657). 



EXPERIMENTAL METHOD - concerted, or- 

 ganized, and scientific analysis of the 

 causes, forces, and factors operating in 

 any (embryological) system. 



EXPERIMENTUM CRUCIS - the final, conclud- 

 ing 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. 



EXPLANTATION - culturing of isolated blas- 

 tema or tissues in vitro. 



EXPRESSIVITY - the degree to which a group of 

 organisms is affected by the presence of a 

 particular gene (see penetrance). 



EXTENSION - process of gastrulation; elonga- 

 tion of central cells of the marginal zone, 

 and then the more peripheral cells, toward 

 the groove of the blastopore. Syn. , elonga- 

 tion, self-stretching (Schechtman), Strekung, 

 Staffelung (Vogt). 



EXTRA-OVATE - extrusion of a portion of the 

 egg substance beyond the cell boundary, 

 achieved in hypotonic solutions. Syn. , 

 exovate. 



EYE, ANTERIOR CHAMBER 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. 



FARBLOSE PIGMENTZELLEN - colorless pig- 

 ment cell in dermal and subcutaneous tissues 

 (e.g., in axolotl). (Schuberg, 1903.) 



FATE MAP - a map of a blastula or early gas- 

 trula 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, PROSPECTIVE - destination towards 

 which we know, from previous experience, 

 that a given part would develop under nor- 

 mal conditions; lineage of each part of the 

 egg through its cell descendants into a defi- 

 nite region or portion of the adult organism. 



FEEDING, MAXIMAL - procedure whereby the 

 organism is provided with all the food that 

 it can possibly consume. 



FETUS PAPYRACEUS - compressed fetus, ab- 

 normal: "paper-doll fetus". 



FERTILIZATION - activation of the egg by a 



spermatozoUn and syngamy of the two pro- 

 nuclei; union of male and female gamete 

 nuclei; amphimixis. 



FERTILIZATION CONE - conical projection of 

 the egg cortex to meet the spermatozoon 

 destined to invade the egg, generally en 



gulfing the spermatozoon. Seen in annelids, 

 moUuscus, echinodernnfs, and ascidians. 



FERTILIZATION, DRY - placing milt (concen- 

 trated sperm) of aquatic forms directly over 

 practically dry eggs, the procedure allowing 

 greater concentration of sperm before flood- 

 ing the eggs with water. 



FERTILIZATION, FRACTIONAL - fertilization 

 following partial removal of sperm by cen- 

 trifugation after partial penetration (Lillie, 

 1912). Elongated heads of some sperm 

 (e. g. , Nereis) are easily fragmented during 

 penetration by centrifugation. 



FERTILIZATION MEMBRANE - a non-living 

 membrane seen to be distinct fronn the egg 

 shortly after fertilization, very probably 

 the vitelline membrane elevated off of the 

 egg (or from which the egg has shrunken 

 away by exosnnosis). (See Costello, 1939: 

 Phys. Zool. 12.) 



FERTILIZATION, PARTIAL - cases where 



sperm head, after entering the egg cortex, 

 does not move fast enough toward the egg 

 nucleus to arrive before cleavage sets in, 

 although the sperm aster may have reached 

 the egg nucleus and given rise to the seg- 

 mentation spindle. 



FERTILIZATION, SELECTIVE - physiological 

 block to some combinations of sperm and 

 egg, such as in cases of self-sterility (e. g. , 

 Ciona). May indicate differential fertilizing 

 powers of spermatozoa even from a com- 

 mon source. 



FERTILIZIN - chemical substance in the egg 



cortex of mature (Echinoderm) eggs, called 

 "sperm isoagglutinin" (Lillie, 1916) since 

 its presence is necessary for fertilization 

 of certain forms. Supposedly possesses 

 two side chains, one spermophile and the 

 other ovophile. Soluble colloidal substance 

 (agglutinin) produced by eggs to attract 

 sperm. 



FERTILIZIN, ANTI - "Eggs contain in their 

 interior a substance capable 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 - Schiff's aldehyde test 

 accomplished by hydrolysis of thymo- 

 nucleic acid to yield the aldehyde which re- 

 acts with fuchsin giving a brilliant violet or 

 pink color, a specific test for the thymo- 

 nucleic acid of chromosomes. 



FIBRILLATION - process of formation of (col- 

 lagenous) fibers by the aggregation of ultra- 

 microns whose axes are nearly parallel. 

 May be the method of axis formation in limb 

 rudiments (Harrison). 



FIELD - nnosaic of spatio-temporal activities 

 within the developing organism constitute 

 fields; areas of instability with positional 

 relations to the whole organism, within 

 which specific differentiations are about to 



